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2024 Volume 3
Article Contents
Abstract
Introduction
Morphological difference, habitat and distribution
Ethnobotanical uses
Ancient medicinal book records
Morphological description
Medicinal effect
Traditional folk application
Chemical constituents
Phenanthrene derivatives
Phenolic acids
Bibenzyls
Flavonoids
Triterpenoids and steroids
Other compounds
Pharmacological activities
Anti-inflammatory
Anti-tumor
Antiviral
Antioxidant
Hemostasis
Antibacterial
Other
Application status and safety evaluation
Conclusions and prospects
Author contributions
Data availability
Acknowledgments
Conflict of interest
Rights and permissions
References
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REVIEW   Open Access    

Transportation mobility during COVID-19: a systematic review and bibliometric analysis

  • 1.

    Department of Civil and Environmental Engineering, Islamic University of Technology, Gazipur - 1704, Bangladesh

  • 2.

    Department of Civil and Resource Engineering, Dalhousie University, 5410 Spring Garden Road, Halifax, NS, B3H4R2, Canada

  • # Authors contributed equally: Aditya Basunia, Azwad Muttaqi

More Information
  • The COVID-19 pandemic has significantly affected global transportation mobility, presenting unprecedented challenges to transportation management. Public transit and ride-hailing services saw a drastic reduction in ridership, leading to an increased inclination towards private vehicles. The pandemic also altered travel patterns and individual mobility due to various COVID-19 protocols. This study conducted a comprehensive review of 96 academic papers spanning from January 1, 2020, to December 31, 2022, focusing on transportation and mobility using the Scopus database. Three major themes were identified: 'Impact on Ride-Hailing Services', 'Impact on Mode Preference', and 'Impact on Trip Purpose', with subdivisions based on keywords and key findings extracted using VOSviewer. The pandemic significantly impacted ride-hailing services, altering demand, usage, and safety measures. Mode preference shifted towards private vehicles due to safety concerns. The present study underscores the long-term implications of the pandemic, emphasizing recovery strategies for ride-hailing services and mode preferences post-pandemic. It highlights the need for sustainable transportation policies, advocating for enhanced public transportation systems, promoting active travel modes, and addressing socioeconomic disparities in mobility patterns. The findings emphasize the need for resilient transportation strategies in the face of future disruptions.

  • Introduction

    Bletilla Rchb. f. is one of the most economically valuable groups of orchids in the world. Due to its ornamental significance, the genus Bletilla occupies an important place in the worldwide horticultural market. Furthermore, in China, Japan, South Korea, and other Asian countries, it is highly valued for its medicinal use[1].

    There are eight species in the genus Bletilla, including Bletilla chartacea (King & Pantl.) Tang & F.T. Wang, Bletilla cotoensis Schltr., Bletilla foliosa (King & Pantl.) Tang & F.T. Wang, Bletilla formosana Schltr., Bletilla guizhouensis J. Huang & G.Z. Chen, Bletilla morrisonensis Schltr., Bletilla ochracea Schltr., and Bletilla striata Rchb.f.[2,3]. The distribution area spans from northern Myanmar in Asia to Japan via China[4]. Five species are native to China, namely, B. foliosa, B. formosana, B. guizhouensis, B. ochracea, and B. striata. In China, people have assigned various names to Bletilla based on its morphology and efficacy, such as baiji (白及/白芨), baigen (白根), baige (白给), baijier (白鸡儿), baijiwa (白鸡娃), diluosi (地螺丝), gangen (甘根), junkouyao (皲口药), lianjicao (连及草), and yangjiaoqi (羊角七)[5]. These diverse appellations highlight the importance of this genus in Chinese folk biological culture.

    The medicinal material known as 'baiji' in traditional Chinese medicine (TCM) is usually the dried tuber of B. striata, which is also the authentic product included in the Chinese Pharmacopoeia[6]. According to the Chinese Pharmacopoeia (2020), TCM baiji is sliced, dried, and crushed into a powder that can be used topically or internally, with a recommended dosage of 3–6 g at a time, offering astringent, hemostatic, detumescence, and myogenic effects. It is often used for conditions such as hemoptysis, hematemesis, traumatic bleeding, sores, and skin chaps[7]. Although only B. striata is the authentic product of TCM baiji, the other four Bletilla species native to China are also used as substitutes, and this practice is widespread[8].

    Modern research indicates that Bletilla contains a variety of chemical components, including benzol, dihydrophenanthrene, phenanthrene, and quinone derivatives. These components confer pharmacological effects on Bletilla, such as hemostasis, anti-tumor activity, and promotion of cell growth[9]. Due to its outstanding medicinal value, Bletilla can be found in nearly every corner of the traditional medicine market (Fig. 1). However, habitat destruction and uncontrolled mining have led to a significant reduction in the native populations of Bletilla, making its protection an urgent priority. Therefore, this paper provides a comprehensive review of relevant research up to August 2023, covering botanical characteristics, resource distribution, ethnobotanical uses, chemical components, pharmacological effects, clinical applications, and safety evaluations of Bletilla. The aim is to raise awareness and promote the protection and sustainable use of this genus.

    Figure 1.  Varieties of Bletilla at the traditional March Medicinal Market in Dali, Yunnan, China.
    DownLoad: Full-Size Img PowerPoint

    Morphological difference, habitat and distribution

    The morphology of different Bletilla species is highly similar. The primary taxonomic feature distinguishing each species is the characteristics of the flower, particularly the lip of the flower, including its size, shape, and the number and shape of longitudinal ridges on the lip plate (Table 1, Fig. 2)[10−14].

    Table 1.  The morphological differences among five species of Bletilla plants native to China.
    Morphological featureBletilla striataBletilla formosanaBletilla ochraceaBletilla foliosaBletilla guizhouensis
    Plant height (cm)18−6015−8025−5515−2045−60
    Rhizome shapeCompressedCompressedSomewhat compressedSubgloboseCompressed
    Rhizome diameter (cm)1−31−2About 21−1.53−4
    Stem characteristicsStoutEnclosed by sheathsStoutStout, shortThin
    Leaf shapeNarrowly oblongLinear-lanceolateOblong-lanceolateElliptic-lanceolateNarrowly lanceolate
    Leaf size (cm)8−29 × 1.5−46−40 × 0.5−4.58−35 × 1.5−2.85−12 × 0.8−325−45 × 1.2−4.5
    Flower colorPurplish red or pinkPale purple or pinkYellowPale purpleDeep purple
    Flower sizeLargeMediumMediumSmall to mediumLarge
    Inflorescence structureBranched or simpleBranched or simpleSimpleSimpleBranched
    Pedicel and ovary length (mm)10−248−12About 187−913−17
    Sepal shapeNarrowly oblongLanceolateLanceolateLinear-lanceolateOblong-elliptic
    Petal shapeSlightly larger than sepalsSlightly narrower than sepalsObliqueLanceolateOblong-elliptic
    Lip shapeObovate-ellipticBroadly ellipticNarrowly rhombic-obovateNarrowly oblongNarrowly oblong
    Lip colorWhite with purplish veinsWhitish to pale yellow with small dark purple spotsWhitish to pale yellow with small dark purple spotsWhite with purplish spots and purple edgeWhite with deep purple edge
    Number of lip Lamellae5 lamellae5 undulate lamellae5 longitudinal lamellae3 fimbriate lamellae7 longitudinal lamellae
    Column characteristicsSubterete, dilated towards apexSubterete, dilated towards apexSlender, dilated towards apexCylindric, dilated towards apexSuberect, with narrow wings
     | Show Table
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    Figure 2.  (a)−(d) Bletilla striata (Thunb. ex Murray) Rchb. f. (e)−(h) Bletilla formosana (Hayata) Schltr. (i)−(l) Bletilla ochracea Schltr. (m), (n) Bletilla sinensis (Rolf) Schltr. (o), (p) Bletilla guizhouensis Jie Huang & G.Z. Chen (Photographed by Wang Meina, Zhu Xinxin, and He Songhua).
    DownLoad: Full-Size Img PowerPoint

    The flowers of B. striata are large and purplish-red or pink, with narrowly oblong sepals and petals measuring 25−30 mm in length and 6−8 mm in width. They have acute apices, nearly as long as the sepals and petals. The lip is obovate or elliptic, predominantly white with purplish-red coloration and purple veins, measuring 23−28 mm in length, slightly shorter than the sepals and petals. The lip disc exhibits five longitudinal folds extending from the base to near the apex of the middle lobe, with waviness occurring only above the middle lobe[11]. In China, B. striata is found in regions such as Anhui, Fujian, Guangdong, Guangxi, Gansu, Guizhou, Hubei, Hunan, Jiangsu, Jiangxi, Shaanxi, Sichuan, and Zhejiang. It also occurs in the Korean Peninsula and Japan, thriving in evergreen broad-leaved forests, coniferous forests, roadside grassy areas, or rock crevices, at altitudes ranging from 100−3,200 m[12].

    B. ochracea's flowers are medium to large, featuring yellow or yellow-green exteriors on the sepals and petals, while the insides are yellow-white, occasionally nearly white. The sepals and petals are nearly equal in length, oblong, measuring 18−23 mm long and 5−7 mm wide, with obtuse or slightly pointed apices, often adorned with fine purple spots on the reverse side. The lip is elliptic, typically white or light yellow, measuring 15−20 mm in length and 8−12 mm in width, with three lobes above the middle. The lip disc is characterized by five longitudinally ridged pleats, with undulations primarily occurring above the middle lobe[13]. B. ochracea is native to southeastern Gansu, southern Shaanxi, Henan, Hubei, Hunan, Guangxi, Guizhou, Sichuan, and Yunnan, thriving in evergreen broad-leaved forests, coniferous forests, or beneath shrubs, in grassy areas or alongside ditches at altitudes ranging from 300−2,350 m[14].

    B. formosana's flowers come in shades of lavender or pink, occasionally white, and are relatively small. The sepals and petals are narrowly oblong, measuring 15−21 mm in length and 4−6.5 mm in width, and are nearly equal in size. The sepals have subacute apices, while the petal apices are slightly obtuse. The lip is elliptic, measuring 15−18 mm in length and 8−9 mm in width, with three lobes above the middle. The lip disc exhibits five longitudinal ridge-like pleats, which are wavy from the base to the top of the middle lobe[15]. B. formosana is indigenous to southern Shaanxi, southeastern Gansu, Jiangxi, Taiwan, Guangxi, Sichuan, Guizhou, central to northwest Yunnan, southeast Tibet (Chayu), and Japan. It is typically found in evergreen broad-leaved forests, coniferous forests, road verges, valley grasslands, grassy slopes, and rock crevices, at altitudes ranging from 600−3,100 m[16].

    The flowers of B. foliosa are small and lavender, with white sepals and petals featuring purple apices. The sepals are linear-lanceolate, measuring 11−13 mm in length and 3 mm in width, with subacute apices. The petals are lanceolate, also measuring 11−13 mm in length and 3 mm in width, with acute apices. The lip is white, oblong, adorned with fine spots, and features a purple apex. It measures 11−13 mm in length and 5−6 mm in width, tapering near the base and forming a scaphoid shape. The lip is anteriorly attenuated, unlobed, or abruptly narrowing with inconspicuous three lobes and exhibits fringe-like fine serrations along the edge. Three longitudinal ridge-like pleats are present on the upper lip disc[17]. B. foliosa typically grows on hillside forests, with its type specimen collected from Mengzi City, Honghe Hani and Yi Autonomous Prefecture, Yunnan Province, China[17].

    B. guizhouensis is a recently discovered species in Guizhou, China. In terms of shape, B. guizhouensis closely resembles B. striata, but it can be distinguished by its ovate-oblong buds, oblong dorsal sepals, obovate lips, and middle lobes of the lips, which are oval in shape. The disc of B. guizhouensis features seven distinct longitudinal lamellae, setting it apart from other known Bletilla species and establishing it as a distinct species[2]. Presently, B. guizhouensis has only been found in Guizhou, China, primarily thriving in evergreen broad-leaved forests at altitudes ranging from 900−1,200 m[3].

    Understanding the morphology, habitat, and distribution of Bletilla species is crucial for the conservation and propagation of these resources. To effectively implement plant conservation and breeding programs, a comprehensive understanding of the specific morphological characteristics, growth environments, and native habitats of these plants is essential, as without this knowledge, effective results cannot be achieved.

    Ethnobotanical uses

    The ethnobotanical uses of Bletilla worldwide primarily fall into two categories: ornamental and medicinal purposes. Bletilla orchids, renowned for their striking and distinct flowers, are commonly cultivated for ornamental purposes across many countries[18]. Valued for their aesthetic appeal, these orchids are frequently grown in gardens and utilized as potted plants. Among the various cultivars, B. striata stands out as the most favored choice for ornamental horticulture due to its ease of cultivation and adaptability to diverse climates[19,20].

    Contrastingly, in select Asian countries, Bletilla assumes a crucial role as a medicinal plant. For instance, influenced by TCM, the tuber of Bletilla also serves as a crude drug for hemostatic and anti-swelling purposes in Japan[21]. Likewise, traditional Korean medicine, deeply rooted in TCM principles, extensively documents the versatile use of Bletilla in addressing issues such as alimentary canal mucosal damage, ulcers, bleeding, bruises, and burns[22]. In Vietnam, Bletilla has been used as a medicinal herb for treating tumors and skin fissures, aligning with practices observed in the ethnic communities of southwest China[23].

    In China, Bletilla boasts a longstanding medicinal history, with numerous classical ancient Chinese medicine books containing detailed records of its medicinal applications[24−32]. Even in contemporary society, many ethnic groups residing in mountainous areas in China continue to uphold the traditional medical practice of using Bletilla medicinally[31].

    Ancient medicinal book records

    Morphological description

    In ancient Chinese medical literature, detailed records of Bletilla's morphology can be traced back to the late Han Dynasty, around 200 AD[24]. The Mingyi Bielu, a historical source, documented, 'Bletilla grows in the valley, with leaves resembling those of Veratrum nigrum L., and its root is white and interconnected. The ideal time for harvesting is September'. As awareness of the medicinal significance of Bletilla grew, successive dynastic-era Chinese medical texts consistently included descriptions of Bletilla's morphology (Table 2). In the Ming Dynasty, Li Shizhen compiled these earlier accounts of Bletilla's plant characteristics in his work, the Compendium of Materia Medica. He even provided an illustrative depiction of this plant genus (Fig. 3)[25].

    Table 2.  Morphological description of the plants belonging to Bletilla in the ancientChinese medicinal books.
    Dynasty (Year)TitleAuthorOriginal ChineseEnglish translation
    Late Han
    (184−220 AD)    		Mingyi Bielu/白给生山谷, 叶如藜芦,
    根白相连, 九月采    		Bletilla grows in the valley, with leaves like Veratrum nigrum L., root is white and connected. September is the time for harvesting.
    Wei-Jin period
    (220−420 AD)    		WuPu BencaoWu Pu白根, 茎叶如生姜, 藜芦,
    十月花, 直上, 紫赤色,
    根白连, 二月, 八月, 九月采    		Bletilla, stems and leaves like Zingiber officinale Roscoe and V. nigrum. It blooms in October and is purple and red, the inflorescence is vertical and upward. The roots are white and connected. It can be dug in February, August, and September.
    the Northern and Southern
    (420−589 AD)    		Bencao JizhuTao Hongjing近道处处有之, 叶似杜若,
    根形似菱米, 节间有毛    		It is everywhere near the road. The leaves are like Pollia japonica Thunb. The roots are like the fruit of Trapa natans L., and internode are many fibrous roots.
    Tang
    (618−907 AD)    		Su Jing, Zhangsun Wuji, etcTang materia medica生山谷, 如藜芦, 根白连, 九月采Born in the valley, with leaves like V. nigrum, root is white and connected. September is the time for harvesting.
    Song
    (960−1279 AD)    		Su SongCommentaries on the Illustrations白芨, 生石山上。春生苗,
    长一尺许, 似栟榈及藜芦,
    茎端生一台, 叶两指大, 青色,
    夏开花紫, 七月结实, 至熟黄黑色。
    至冬叶凋。根似菱米, 有三角白色, 角端生芽。二月, 七月采根    		Bletilla grow on the stone hill. It sprouts in spring and grows about a foot long. The seedlings are like Trachycarpus fortunei (Hook.) H. Wendl. and V. nigrum. The leaves are two finger-size. In summer, it blooms purple flowers and bears fruit in July. The ripe fruit is yellow-black. The leaves wither in winter. The root is like the fruit of T. natans, with three corners, white, and sprouting at the corners. The roots are dug in February and July.
    Ming
    (1368−1644 AD)    		Li ShizhenCompendium of Materia Medica一棵只抽一茎, 开花长寸许,
    红紫色, 中心如舌, 其根如菱米,
    有脐, 如凫茈之脐,
    又如扁扁螺旋纹, 性难干    		Only one stem per herb. The flower is more than one inch long, red and purple, and the center resembles a tongue. Its root is similar to the fruit of T. natans, possessing an umbilicus akin to that of Eleocharis dulcis (N. L. Burman) Trinius ex Henschel. It has spiral veins and is challenging to dry.
    −, Anonymous.
     | Show Table
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    Figure 3.  Bletilla in Compendium of Materia Medica.
    DownLoad: Full-Size Img PowerPoint

    Generally, ancient Chinese medical texts did not make clear distinctions between different Bletilla species. They collectively referred to plants with similar morphological traits as 'baige', 'baigen', 'baiji', 'gangen', 'lianjicao', or 'ruolan'. However, through textual analysis, it has been established that the descriptions of Bletilla in ancient texts before the Ming Dynasty largely align with Bletilla striata in terms of plant height, pseudo-bulb shape, leaf morphology, flower and fruit colors, and other characteristics. While the Bletilla portrayed in attached images may not precisely match B. striata in terms of morphology, considering the textual descriptions, it generally corresponds with B. striata. In writings from the Ming Dynasty and later periods, more specific descriptions of Bletilla emerged, encompassing details about its vascular arrangement, inflorescence, and flower structure, which consistently align with B. striata. Consequently, researchers have corroborated that the original plant of Bletilla described in ancient texts is Bletilla striata[24,33].

    Medicinal effect

    According to the ancient Chinese medicinal books, Bletilla was used to treat a wide variety of conditions, including coughing, bruising, and bleeding, but their most mentioned use in ancient Chinese texts is for skin whitening and freckle removal[25]. Since ancient times, Bletilla species have been used consistently for skin care and whitening, and there are many well-known skincare products related to Bletilla. These Chinese formulae with Bletilla are similar to modern facial masks, face creams, facial cleanser, hand creams and other skin care products[26].

    For example, a prescription for 'facial fat (面脂)' in Medical Secrets from the Royal Library (752 AD) is made by boiling Bletilla with other traditional ingredients, and is applied to the face, resulting in skin whitening, freckle and wrinkle removal[27]. The 'Angelica dahurica cream (白芷膏)' in the General Medical Collection of Royal Benevolence (1111−1125 AD) is reputed to whiten facial skin through a seven-day treatment regiment, and contains Bletilla as the main botanical ingredient along with Angelica dahurica[28]. Jingyue Quanshu (1563-1640 AD) also contains a prescription called 'Yurong powder (玉容散)' for facial skin care. 'Yurong powder' is made of a fine powder of Bletilla, Nardostachys jatamansi (D. Don) DC., Anthoxanthum nitens (Weber) Y. Schouten & Veldkamp and other herbs[29]. Washing the face with Yurong powder in the morning and evening every day is said to make a person's face white without blemishes (Fig. 4)[29].

    Figure 4.  Yurong powder made of Bletilla and other traditional Chinese medicines in Jingyue Quanshu.
    DownLoad: Full-Size Img PowerPoint

    In addition, in ancient Chinese medicine texts, Bletilla is also a well-known medicine for treating hematemesis, hemoptysis and bruises[23]. According to Shennong's Classic of Materia Medica (25−220), grinding the white fungus into fine powder and taking it after mixing with rice soup can be effective for treating lung damage and hematemesis[30]. Among the Prescriptions for Universal Relief (1406), 18 traditional Chinese medicines, such as Bletilla, are used to make 'snake with raw meat cream', which is said to be useful to treat carbuncles and incised wounds[31]. There is also a record of Bletilla powder treating lung heat and hematemesis in the Collected Statements on the Herbal Foundation (1624)[32].

    In ancient Chinese medicinal texts, most Bletilla are said to be useful for lung injury and hemoptysis, epistaxis, metal-inflicted wounds, carbuncles, burns, chapped hands and feet, whitening and especially for skin care. In the ancient medicinal texts, Bletilla is used alone or mixed with other traditional Chinese medicines. It is usually used in the form of a powder. The various medicinal effects of Bletilla described in these ancient texts suggest the great potential of this genus in clinical application, especially in the market of skin care products and cosmetics.

    Traditional folk application

    As a skin care herb praised by ancient medical classics, 11 ethnic minorities in China, such as Bai, Dai, De'ang, Jingpo, Lisu, Miao, Mongolian, Mulao, Tu, Wa, and Yi still retain the traditional habit of using Bletilla for skin care in their daily life (Table 3). In addition to B. striata, B. formosana and B. ochracea are also used as substitutes. Although Chinese ethnic groups have different names for Bletilla spp., the skin care methods are basically the same. Dry Bletilla tubers are ground into a powder and applied to the skin[34], and this usage is also confirmed by the records in ancient medical texts[23, 24]. The various local names of Bletilla by different ethnic groups also indirectly suggests which ethnic groups play an important role in the traditional use. For example, Bai people called B. striata baijier (白鸡儿), goubaiyou (狗白尤), and yangjiaoqi (羊角七) (Table 3).

    Table 3.  The traditional medicinal knowledge of Bletilla in ethnic communities, China.
    Ethnic groupLatin nameLocal nameUsed partUse methodMedicinal effect
    AchangBletilla striata (Thunb. ex Murray) Rchb. F.BaijiTuberAfter the roots are dried, chew them orally or grind them into powder for external applicationTuberculosis, hemoptysis, bleeding from gastric ulcer, burns and scalds
    BaiBaijier, Goubaiyou, YangjiaoqiTuberTreatment of tuberculosis hemoptysis, bronchiectasis hemoptysis, gastric ulcer hemoptysis, hematochezia, skin cracking
    DaiYahejieTuberUsed for tuberculosis, tracheitis, traumatic injury, and detumescence
    De'angBageraoTuberTuberculosis, hemoptysis, bleeding from gastric ulcer, burns and scalds
    DongShaque, SanjueTuberTreat hematemesis and hemoptysis
    JingpoLahoiban, PusehzuotuberFor tuberculosis, bronchiectasis, hemoptysis, gastric ulcer, hematemesis, hematuria, hematochezia, traumatic bleeding, burns, impotence
    MengMoheeryichagan, NixingTuberFor tuberculosis hemoptysis, ulcer bleeding, traumatic bleeding, chapped hands, and feet
    MiaoBigou, Wujiu, SigouTuberUsed for hemoptysis of tuberculosis, bleeding of ulcer disease, traumatic bleeding, chapped hands, and feet
    MolaoDajiebaTuberTreat internal and external injuries caused by falls
    TibetanSanchabaijiTuberFresh chopped and soaked with honey; Powdered after sun-dried, then taken with honey and waterMainly used to treat cough, asthma, bronchitis, lung disease and a few gynecological diseases
    TuRuokeyeTuberAfter the roots are dried, chew them orally or grind them into powder for external applicationTreatment of tuberculosis, hemoptysis, bloody stool, chapped skin
    WaBaijiTuberAfter the roots are dried, chew them orally or grind them into powder for external applicationFor tuberculosis, hemoptysis, gastrointestinal bleeding, scald and burn
    YaoBiegeidaiTuberTreat gastric ulcer, pulmonary tuberculosis, cough, hemoptysis, and hematemesis
    YiDaibaij, Tanimobbaili, Niesunuoqi, AtuluoboTuberTreatment of tuberculosis, hemoptysis, golden wound bleeding, burns, chapped hands and feet
    ZhuangManggounuTuberTreat stomachache and hemoptysis
    BaiBletilla formosana (Hayata) Schltr.Baijier, YangjiaoqiTuberAfter the roots are dried, chew them orally or grind them into powder for external applicationIt is used for emesis, hemoptysis due to tuberculosis, and hemoptysis due to gastric ulcer. External application for treatment of incised wound
    MiaoLianwuTuberThe effect is the same as that of B. striata
    LisuHaibiqiuTuberIt can treat tuberculosis, hemoptysis, epistaxis, golden sore bleeding, carbuncle and swelling poison, scald by soup fire, chapped hands and feet
    YiNiesunuoqi, Yeruomaoranruo, Atuluobo, Ribumama, Atuxixi, Abaheiji, Binyue, ZiyouTuberIt is used for tuberculosis, hemoptysis, traumatic injury, treatment of frostbite, burn, scald, bed-wetting of children and other diseases
    BaiBletilla ochracea Schltr.Baijier, YangjiaoqiTuberAfter the roots are dried, chew them orally or grind them into powder for external applicationFor hematemesis, epistaxis, hemoptysis due to tuberculosis, hemoptysis due to gastric ulcer; External application of golden sore and carbuncle
    MengMoheeryichagan, NixingtuberThe effect is the same as that of B. striata
     | Show Table
    DownLoad: CSV

    The formation of traditional medical knowledge among Chinese people is often directly related to the specific living environment and cultural background[34]. For example, the Bai, Dai, De'ang, Jingpo, Lisu Yi, Wa and other ethnic minorities live in mountainous areas. The cold weather in winter and year-round outdoor manual work makes it difficult to maintain their skin[35, 36]. In the face of this situation, the ethnic people who are concerned about their physical appearance have long ago chosen local Bletilla species for skin care, and have handed down this tradition for many generations[34]. This important traditional skin care tradition is worthy of further in-depth study.

    Chemical constituents

    The six main classes of Bletilla chemical components, phenanthrene derivatives, phenolic acids, bibenzyls, flavonoids, triterpenoids, and steroids, have been described previously. Almost three hundred compounds have been isolated from Bletilla, including 116 phenanthrene derivatives, 58 phenolic acids, 70 bibenzyls, 8 flavonoids, 24 triterpenoids and steroid and 13 other compounds (Figs 5−14). Chemical structures of the isolates of Bletilla species most are phenanthrene derivatives, which have been demonstrated to possess various pharmacological activities.

    Phenanthrene derivatives

    The prominent opioids oxycodone, hydrocodone, naloxone, and naltrexone are all phenanthrene derivatives[37]. Currently, phenanthrene derivatives (Fig. 5, 1 to 66) were isolated from B. formosana, B. ochracea, and B. striata. In 2022, 17 phenanthrene derivatives (1–17) were isolated from the ethyl acetate (EtOAc) extracts of B. striata tubers[38]. Then, other phenanthrene derivatives were isolated from Bletilla, such as dihydrophenanthrenes (18–41), phenanthrenes (42–66), biphenanthrenes (Fig. 6, 67–89), dihydro/phenanthrenes with uniquestructures (90–112) and phenanthraquinones (Fig. 7, 113–116). Thus far, this genus has been documented to include these compounds, which have been shown to exhibit pharmacological actions[39−45].

    Figure 5.  Phenanthrene derivatives from Bletilla species (1−66)[38−41,43−45,47,49,58,70−72,74−79].
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    Figure 6.  Phenanthrene derivatives from Bletilla species (67−105)[41,43,49,59−61,70,76,79−86].
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    Figure 7.  Phenanthrene derivatives from Bletilla species (106−116)[43,49,70,75,84,85,87].
    DownLoad: Full-Size Img PowerPoint

    Phenolic acids

    Phenolic acids are carboxylic acids created from the skeletons of either benzoic or cinnamic acids[46−48]. Fifty-eight phenolic acids (Figs 8−10, 117 to 174) were isolated from B. formosana, B. ochracea, and B. striata.

    Figure 8.  Phenolic acids from Bletilla species (117−134)[1,5,36,47−52,54,67,88,90].
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    Figure 9.  Phenolic acids from Bletilla species (135−169)[39,45,48−54,56,61,68,69,73,76,82,83,89−94].
    DownLoad: Full-Size Img PowerPoint
    Figure 10.  Phenolic acids from Bletilla species (170−174)[20,95].
    DownLoad: Full-Size Img PowerPoint

    For example, compounds 121, 126, 139, 141, 148, 149, 154, 155 and 157 were isolated from the rhizomes of B. formosana[1,49,50−52]. The structures of these compounds were determined, mostly from their NMR spectroscopy data. Additionally, protocatechuic (136) and vanillin (137) also have been isolated from B. striata[53]. Moreover, some bioactive components such as 2-hydroxysuccinic acid (164) and palmitic acid (165) have been discovered and identified from B. striata[20,54−56].

    Bibenzyls

    The bibenzyls were small-molecular substances with a wide range of sources, which were steroidal ethane derivatives and resembling the structural moiety of bioactive iso-quinoline alkaloids[57].

    For example, depending on their structural characteristics, 70 bibenzyl compounds (Fig. 11, 175 to 244) can be grouped into three groups, simple bibenzyls (175–186, 233–238), complex bibenzyls (189–225) and chiral bibenzyls (226-232, 239-244)[58−60].

    Figure 11.  Bibenzyls from Bletilla species (175-244)[1,40−42,47,49,50,58−60,70,73,76,96−99].
    DownLoad: Full-Size Img PowerPoint

    Flavonoids

    Flavonoids are among the most common plant pigments. Eight bibenzyls (Fig. 12, 245 to 252) have been isolated from B. formosana, B. ochracea, and B. striata. Apigenin (245) and 8-C-p-hydoxybenzylkaempferol (249) were isolated from the whole plant of B. formosana[45]. Bletillanol A (250), bletillanol B (251) and tupichinol A (252) were isolated from B. striata[61]. The names and chemical structures of the flavonoids reported from Bletilla are shown below (Fig. 12).

    Figure 12.  Flavonoids from Bletilla species (245–252)[45,61].
    DownLoad: Full-Size Img PowerPoint

    Triterpenoids and steroids

    Twenty-four triterpenoids and steroids (Fig. 13, 253 to 276) have been reported from Bletilla (Fig. 13), such as, tetracyclic triterpenes (253–259) and pentacyclic triterpenes (189–225) and chiral bibenzyls (260)[62−64]. Steroids (261–276) isolated from the Bletilla and have shown some bioactivity. For example, bletilnoside A (272) was isolated from Bletilla species and displayed anti-tumor activity[65,66].

    Figure 13.  Triterpenoids and steroid compounds from Bletilla species (253-276)[56,62−65].
    DownLoad: Full-Size Img PowerPoint

    Other compounds

    Thirteen other compounds (Fig. 14, 277 to 289) were isolated from B. formosana, B. ochracea, and B. striata. These compounds included amino acids, indoles and anthraquinones[67,68]. For example, syringaresinol (285) and pinoresinol (286) have been described in the methanol extract of the tubers of B. striata[61].

    Figure 14.  Others compounds from Bletilla species (277−289)[50,54,61,62,67,68,94,97].
    DownLoad: Full-Size Img PowerPoint

    Based on the information about the chemical constituents of Bletilla species, it appears that there is a substantial body of research on these compounds. However, there are some areas that may warrant further investigation and research. At first, it would be valuable to investigate potential synergistic effects and interactions between the different classes of compounds within Bletilla species, as some of the compounds may work together. Besides, it is worth considering the improvement of compound yield. Optimizing extraction methods and finding the most efficient and environmentally friendly techniques are vital for both research purposes and potential commercial applications. It is also important to take into account the variability in chemical composition among different Bletilla species and even within the same species from different cultivars.

    Pharmacological activities

    The rich and varied chemical components make the plants of Bletilla have a wide variety of pharmacological activities (Table 4). Many studies have shown that the plants of this genus have anti-inflammatory, antineoplastic, antiviral, antioxidant, hemostatic, antibacterial, and other biological activities, which help to support the traditional medicinal practice of Bletilla in folk medicine.

    Table 4.  Summary of the pharmacological activities of Bletilla species.
    Pharmacological activityTested substance/partTested system/organ/cellTested dose/dosing methodResultsRefs.
    Anti-inflammatoryEthanol extract of Bletilla striataRAW264.7 cells RAW264.7 cells were pre-treated with ethanol extract of B. striata for 1 h and then stimulated with LPS (200 ng/mL) for 12 h, 0.05% DMSO was applied as the parallel solvent control. The culture supernatant was collected for IL-6 and TNF-α detection.Ethanol extract of B striata significantly inhibited LPS-induced interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) expression at 2.5 µg/mL.[41]
    The ethyl acetate-soluble (EtOAc) extract of tubers of B. striataH2O2-induced PC12 cell injury modelPC12 cells were seeded in 96-well multiplates at a density of 1.5 × 105 cells/mL. After overnight incubation at 37 °C with 5% CO2, 10 μM test samples and H2O2 (final concentration of 450 μM) were added into the wells and incubated for another 12 h.It protected the cells with the cell viabilities of 57.86 ± 2.08%, 64.82 ± 2.84%, and
    64.11 ± 2.52%.    		[98]
    Ethanol extract of tubers of B. striataRAW264.7 cellsCells were treated with ethanol extracts (25 μM) dissolved in DMSO, in the presence of
    1 μg/mL lipopolysacchride
    (LPS) for 18 h    		The anti-inflammatory activity with IC50 of 2.86 ± 0.17 μM.[54]
    PE extract of the tubers of B. striataLPS-stimulated BV2 cellsCells treated with extract
    (0, 1, 10, 30, 100 μg/mL) and dihydropinosylvi (0, 1, 10, 30, 100 μM) in presence of LPS
    (1 μg/mL)    		The anti-inflammatory activity with IC50 values of 96.0 μM.[96]
    Ethanol extract of the roots of B. striataCox-1 and Cox-2Treated with the ethanol extracts at various concentrations
    (0, 1, 10, 100 μM)    		The compounds with sugar moieties displayed selective inhibition of Cox-2 (N90%).[38]
    B. striata polysaccharide (BSPb)Human mesangial cells (HMCs)HMCs were pre-treated with BSPb (5, 10, 20 μg/mL)BSPb efficiently mediated expression of NOX4 and TLR2, to attenuate generation of ROS and inflammatory cytokines.[12]
    Compounds extracted from the rhizomes of Bletilla ochraceaRAW264.7 cellsAfter 24 h preincubation,
    cells were treated with serial dilutions in the presence of
    1 μg/mL LPS for 18 h. Each compound was dissolved in DMSO and further diluted in medium to produce different concentrations. NO production in the supernatant was assessed by adding 100 μL of Griess regents.    		It showed the inhibitory effects with IC50 values in the range of 15.29–24.02 μM.[76]
    Compounds extracted from the rhizomes of B. ochraceaMurine monocytic RAW264.7 cellsAfter 24 h preinubation, RAW 264.7 cells were treated with compounds (25 μM) dissolved in DMSO, in the prenence of
    1 μg/mL LPS for 18 h. NO production in each well was assessed by adding 100 μL of Giress regent    		It showed the inhibitory effects with IC50 2.86 ± 0.17 μM.[86]
    Compounds extracted from the rhizomes of Bletilla formosanaElastase Release AssaysNeutrophils (6 × 105 cells/mL) were equilibrated in MeO-Suc-Ala-Ala-Pro-Val-p-nitroanilide (100 μM) at 37 °C for 2 min and then incubated with a test compound or an equal volume of vehicle (0.1% DMSO, negative control) for 5 min.Most of the isolated compounds were evaluated for their anti-inflammatory activities. The results showed that IC50 values for the inhibition of superoxide anion generation and elastase release ranged from 0.2 to 6.5 μM and 0.3 to 5.7 μM, respectively.[49]
    Anti-tumorTwo compounds from Bletilla striataA549 cellsCompounds were tested for their ability to induce ROS generation in A549 cells at concentrations of 20 two compounds for 24 h, the cells were harvested to evaluate the ROS production.The two compounds exhibited antiproliferative effects using the MTT test; these effects may be due to cell cycle arrest and inducing ROS generation.[87]
    Stilbenoids from B. striataBCRP-transduced K562 (K562/BCRP) cells—It showed antimitotic activity and inhibited the polymerization of tubulin at IC50 10 μM.[78]
    Compounds extracted from the rhizomes of B. ochraceaThe human tumor cell lines HL-60 (acute leukemia), SMMC-7721 (hepatic cancer), A-549 (lung cancer), MCF-7 (breast cancer), and SW480 (colon cancer)100 μL of adherent cells were seeded into each well of 96-well cell culture plates. After 12 h of incubation at 37 °C, the test compound was added. After incubated for 48 h, cells were subjected to the MTS assay.All isolated metabolites except 7 were evaluated for cytotoxic activity against five human cancer cell lines (HL-60, SMMC7721, A-549, MCF-7 and SW480).[76]
    AntiviralThe tuber of B. striataMadin-Darby canine kidney model and embryonated eggs modelAs simultaneous treatment with 50% inhibition concentration (IC50) ranging from 14.6 ± 2.4 to 43.3 ± 5.3 μM.Phenanthrenes from B. striata had strong anti-influenza viral activity in both embryonated eggs and MDCK models.[107]
    The 95% ethanol
    Extract of B. striata    		BALB/C mice—It has significant anti-influenza
    virus effect in mice, which may be related to the increase of IL-2, INFα, INF-β and thus enhance the immune function of mice.    		[12]
    AntioxidantCompounds extracted from the rhizomes of B. formosanaDPPH radical-scavenging assaySolutions containing 160 μL of various concentrations of sample extract, 160 μL of various concentrations of BHA, 160 μL of various concentrations of ascorbic acid, and the control (160 μL of 75% methanol) were mixed separately with 40 μL of 0.8 mM DPPH dissolved in 75% methanol. Each mixture was shaken vigorously and left to stand for 30 min at room temperature in the dark.Tthe seedlings grown by tissue culture of B. formosan collected in Yilan County had the best antioxidant capacity. In addition, B. formosana collected in Taitung County had the best scavenging capacity in the tubers, leaves and roots.[93]
    Fibrous roots of B. striataDPPH model and superoxide anion systemThe ABTS+ solution was prepared by reacting 7 Mm ABTS with 2.45 mM potassium persulfate (final concentrations both dissolved in phosphate buffer, 0.2 M, pH 7.4) at room temperature for 12–16 h in the dark.It removed free radicals and inhibit tyrosinase activity.[33]
    B. striata extracts (BM60)The murine macrophage cells NR8383, male SD mice (180~200 g)NR8383 were pretreated with extracts (1, 10 and 100 g/mL) for 4 h and then 65 stimulated with 1 g/mL of LPS for 24 h. Acute lung injury was induced in mice by nonhexposure intratracheal instillation of LPS (3.0 mg/kg). Administration of the BM60 extract of 35, 70, and 140 mg/kg (L, M, H) was performed by oral gavages.The BM60 treatment reduced the production of NO in NR8383 macrophages. Treatments with BM60 at the doses of 35, 70, 140 mg/kg significantly reduced macrophages and
    neutrophils in the bronchoalveolar lavage fluid (BALF).    		[12]
    The crude
    polysaccharides obtained from B. striata    		DPPH free radical scavenging activityConcentration
    range of 2.5–5.0 mg/mL    		The IC50 of BSPs-H was 6.532 mg/mL.[35]
    HemostasisB. striata polysaccharide (BSP)Diabetes mellitus (DM) mouse models were induced by high fat-diet feeding combined with low-dose streptozocin injectionDM mouse models were induced by high fat-diet feeding combined with low-dose streptozocin injection. The BSP solutions were applied on the surface of each wound at a volume of 50 μl. RD mice were assigned as normal controls and received saline treatment (n = 6). All mice were treated with vehicle or BSP once daily from the day of wounding (d0) until 12 days later (d12).BSP administration accelerated diabetic wound healing, suppressed macrophage infiltration, promoted angiogenesis, suppressed NLRP3 inflammasome activation, decreased IL-1β secretion, and improved insulin sensitivity in wound tissues in DM mice.[112]
    B. striata Micron Particles (BSMPs)Tail amputation model and healthy male Sprague-Dawley (SD) rats
    (250 ± 20 g, 7 weeks of
    age)    		Rats were divided into six groups of five treated with cotton gauze and BSMPs (350–250, 250–180, 180–125, 125–75, and < 75 μm), respectively.Compared to other BSMPs of different size ranges, BSMPs of 350–250 μm are most efficient in hemostasis. As powder sizes decrease, the degree of aggregation between particles and hemostatic BSMP effects declines.[109]
    Rhizoma Bletillae polysaccharide (RBp)Adult male SD rats weighing 220 ± 20 gAfter incubation for 1 min at 37 °C, 300 μL of PRP was dealt with different concentrations of RBp (50, 100, 150, and 200 mg/L) under continuous stirring, and the vehicle was used as the blank control.RBp significantly enhanced the platelet aggregations at concentrations of 50−200 mg/L in a concentration-dependent manner.[113]
    AntibacterialBibenzyl derivatives from the tubers of Bletilla striataS. aureus ATCC 43300, Bacillus subtilis ATCC 6051, S. aureus ATCC 6538 and Escherichia coli ATCC 11775Using a microbroth dilution method, bacteria were seeded at
    1 × 106 cells per well (200 μL) in a
    96-well plate containing Mueller-Hinton broth with different concentrations (from 1 to 420 μg/mL, 300 μg/mL and so on;
    2-fold increments) of each test compound.    		It showed inhibitory activities with MIC of (3–28 μg/mL) against S. aureus ATCC6538[116]
    The crude extract of B. striataS. album, A. capillaris, C. cassiaThey were seeded at 1 × 106 cells per well (200 μL) in a 96-well plate containing Mueller−Hinton broth (meat extracts 0.2%, acid digest of casein 1.75%, starch 0.15%) with different concentrations (from 1 to 128 μg/mL; 2-fold increments) of each test compound.It showed S. album (0.10%), A. capillaris (0.10%), and C. cassia (0.10%) to have the strongest antibacterial properties.[118]
    The ethyl acetate-soluble (EtOAc) extract of tubers of B. striataS. aureus ATCC 43300, S. aureus ATCC 6538, and Bacillus subtilis ATCC 6051) and Escherichia coli ATCC 11775)Bacteria were seeded at 1 × 106 cells per well (200 μL) in a 96-well plate containing Mueller Hinton broth with different concentrations (from 1 to 420 μg/ml; 2-fold increments) of each test compound.The extract was effective against three Gram-positive bacteria with minimum inhibitory concentrations (MICs) of 52–105 μg/ml.[98]
    The phenanthrene fraction (EF60) from the ethanol extract of fibrous roots of Bletilla striata pseudobulbsS. aureus ATCC 25923, S. aureus ATCC 29213, S. aureus ATCC 43300, E. coli ATCC 35218, and P. aeruginosa ATCC 27853, Bacillus subtilis 168EF60 was active against all tested strains of Staphylococcus aureus, including clinical isolates and methicillin-resistant S. aureus (MRSA). The minimum inhibitory concentration (MIC) values of EF60 against these pathogens ranged from 8 to 64 μg/mL.EF60 could completely kill S. aureus ATCC 29213 at 2× the MIC within 3 h but could kill less than two logarithmic units of ATCC 43300, even at 4× the MIC within 24 h. The postantibiotic effects (PAE) of EF60 (4× MIC) against strains 29213 and 43300 were 2.0 and 0.38 h, respectively.[117]
    Anti-adhesiveBletilla striata extraction solutionPPA was induced by cecal wall abrasion, and Bletilla striata was injected to observe its efect on adhesion in ratsThe rats in the sham operation group was not treated; the other rats of the three experimental groups were intraperitoneally injected with 8 ml of phosphate-buffered saline (Control group), 15% Bletilla striata extraction solution (BS group), and 0.2% hyaluronic acid solution (HA group), respectively.Bletilla striata decreased the development of abdominal adhesion in abrasion-induced model of rats and reduced the expression of the important substance which increased in PPAs.[120]
    ImmunomodulatoryB. striata polysaccharide (BSPF2)Mouse spleen cellsTo observe the immune activity of BSPF2, mouse spleen cells were stimulated with BSPF2 at 10–100 g/mL for 72 h.Immunological assay results demonstrated that BSPF2 significantly induced the spleen cell proliferation in a dose-dependent manner.[121]
    Anti-pulmonary fibrosisB. striata polysaccharideClean grade male SD ratsSD rats were randomly divided into 5 groups, sham operation group (equal volume of normal saline), model group (equal volume of normal saline), tetrandrine positive control (24 mg/kg) group and white and Polysaccharide low
    (100 mg/kg) and high (400 mg/kg) dose groups.    		The Bletilla striata polysaccharide has remarkable regulation effect on anti-oxidation system and immune system, but cannot effectively prevent lung fibrosis.[127]
    Small molecule components of Bletilla striataClean grade male SD ratsSD rats were randomly divided into 5 groups, sham operation group (0.5 mL normal saline), model group (0.5 mL normal saline), and positive control group (tetrandrine 24 mg/kg) and low (20 mg/kg) and high (40 mg/kg) dosage groups of the small molecule pharmacological components of Bletilla, which were administered by gavage once a day for 2 consecutive months.The small molecule components of Bletilla striata can effectively prevent lung fibrosis though regulating the anti-oxidation system，immune system and cytokine level; SMCBS is one of the active components of Bletilla striata on silicosis therapy[124]
    —, not given.
     | Show Table
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    Anti-inflammatory

    Many phytochemicals have been well characterized to lessen swelling or inflammation[89]. A series of phenolic acid and polysaccharide compounds isolated from Bletilla demonstrated anti-inflammatory bioactivity against BV-2 microglial, RAW 264.7, and PC12 cells[96,100−102]. For example, phochinenin K (106) exhibited growth inhibitory effects with an IC50 of 1.9 μM, and it is a possible candidate for development as neuroinflammation inhibitory agent[43]. Using the H2O2-induced PC12 cell injury model, (7S)-bletstrin E (242), (7R)-bletstrin F (243) and (7S)-bletstrin F (244) could clearly protect the cells with the cell viabilities of 57.86% ± 2.08%, 64.82% ± 2.84%, and 64.11% ± 2.52%, respectively[98]. With an IC50 of 2.86 ± 0.17 μM, 2,7-dihydroxy-4-methoxyphenanthrene (53) showed potential action against NO generation in RAW 264.7 macrophages[54]. The use of Bletilla in traditional skin care, it is said to function as an astringent, hemostatic and wound healing[33]. Modern medical pharmacology research has validated that this plant has antibacterial effects, which may may help to explain, in part, its traditional use in skin care[24].

    Though it's mentioned that some of these compounds from Bletilla have demonstrated anti-inflammatory action, more extensive studies are needed to fully understand their mechanisms of action, potential therapeutic applications, and safety profiles. Conducting in vivo studies and clinical trials can provide more concrete evidence of their effectiveness.

    Anti-tumor

    There are important antineoplastic agents that have originated from plant natural products[103]. In recent years, several bibenzyl and flavonoid compounds have been discovered from Bletilla that have antineoplastic activity against A549 cells and other cells. For example, 7-hydroxy-2-methoxy-phenanthrene-3,4-dione (160) and 3′,7′,7-trihydroxy-2,2′,4′-trimethoxy-[1,8′-biphenanthrene]-3,4-dione (163) have shown strong antiproliferative effects and induced ROS production after 24 h in A549 cells[87]. The doxorubicin (Dox)/FA (folate)-BSP-SA (stearic acid) modified Bletilla striata polysaccharide micelles boosted the drug enrichment in tumors and improved the in vivo anticancer effects[104,105]. Micelles, nanoparticles, microspheres, and microneedles are examples of B. striata polysaccharide-based drug delivery systems that exhibit both drug delivery and anti-cancer functionality. These experiments confirmed that some of the compounds isolated from the Bletilla have potential activity for the treatment of cancer.

    However, most of the evidence presented in the previous studies is based on in vitro experiments or cell culture studies. It is highly necessary to use animal models to study the in vivo anti-tumor effects of Bletilla extracts or compounds. These studies can help evaluate the safety and effectiveness of treatments based on Bletilla. Additionally, through such methods, researchers can further investigate the mechanisms of Bletilla's anti-tumor activities, exploring how Bletilla compounds interact with cancer cells, immune responses, and signaling pathways involved in tumor growth and metastasis.

    Antiviral

    Antiviral medications are essential for preventing the spread of illness, and are especially important nowadays with pandemics and drug-resistant viral strains[5, 6]. Therefore, it is vitally necessary to find novel, safe, and effective antiviral medications to treat or prevent viral infections[106]. B. striata plant contains compounds that have been recorded in ancient texts to cure cough, pneumonia, and skin rashes, and these may be related to potential antiviral constituents[23]. Some constituents of B. striata have antiviral activity, for example, phenanthrenes and diphenanthrenes from B. striata displayed potent anti-influenza viral in a Madin-Darby canine kidney model and embryonated eggs model, diphenanthrenes with parentally higher inhibitory activity than monophenanthrenes[107]. But more research is needed to further determine the antiviral activity of Bletilla, understand how Bletilla compounds interact with viral proteins or the host immune response, and conduct safety and toxicity studies, which are crucial for the development of related materials.

    Antioxidant

    Free radicals have the potential to exacerbate lipid peroxidation and harm cell membranes, which can lead to several prevalent human diseases, including cancer, cataracts, and coronary heart disease[108]. Research has shown that extracts from Bletilla possess strong antioxidant activity. However, this antioxidant activity can vary depending on the different growing environments of the plant. Additionally, the antioxidant capabilities of extracts from different parts of the Bletilla plant also vary[93]. Clinical studies have shown that traditional Chinese medicine formulas containing Bletilla can inhibit tyrosinase activity and possess antioxidant properties, thus resulting in skin-whitening effects[108]. Furthermore, some research reveals that the polysaccharides in the plant exhibit significant antioxidant activity, effectively scavenging free radicals and inhibiting tyrosinase activity[33]. This highlights the skin-whitening potential of the fibrous root of Bletilla striata, indicating promising prospects for the comprehensive utilization of the B. striata plant[33]. However, most studies on the pharmacological activities of Bletilla have focused solely on B. striata, neglecting other species within the genus. Different species may possess varying phytochemical compositions and antioxidant properties, which can lead to an incomplete understanding of the genus as a whole.

    Hemostasis

    Available hemostatic agents are expensive or raise safety concerns, and B. striata may serve as an inexpensive, natural, and promising alternative[109]. Polysaccharides of B. striata displayed hemostatic activity through inhibition of the NLRP3 inflammasome[110−112]. The ADP receptor signaling pathways of P2Y1, P2Y12, and PKC receptors may be activated as part of the hemostasis[113]. Alkaloids from Bletilla have hemostatic activities through platelet deformation, aggregation, and secretion. In addition, polysaccharides of Bletilla striata have potential wound-healing medicinal value[110]. Currently, Bletilla plants have been used in various traditional systems, such as traditional Chinese medicine and Ayurveda, to control bleeding.

    Antibacterial

    Previous studies revealed that Bletilla displayed antibacterial effects[114]. For example, bletistrin F, showed inhibitory activities with MIC of (3–28 μg/mL) against S. aureus ATCC 6538[115,116]. Antimicrobial screening of Bletilla showed S. album (0.10%), A. capillaris (0.10%), and C. cassia (0.10%) to have the strongest antibacterial properties[117,118]. In addition, phenanthrenes are worthy of further investigation as a potential phytotherapeutic agent for treating infections caused by S. aureus and MRSA[119]. However, further in vivo studies on the antibacterial activity of Bletilla are lacking, which is needed for clinical application. For example, the specific mechanism of antibacterial activity of Bletilla still needs to be elucidated. While research on the antibacterial activity of Bletilla plants is promising, it faces several shortcomings and challenges that need to be addressed for a more comprehensive understanding of their potential therapeutic applications. Further studies with standardized methodologies, mechanistic insights, clinical trials, and consideration of ecological and safety concerns are essential to advance this field.

    Other

    There are other pharmacological activities of Bletilla, like anti-fibrosis activity, anti-adhesive activity, and immunomodulatory activity. For example, B. striata has been studied as a new and cheaper antiadhesive substance which decreased the development of abdominal adhesion abrasion-induced model in rats[120]. However, the natural resources of Bletilla are also getting scarcer. To preserve the sustainable development of Bletilla species, proper farming practices are required, along with the protection and economical use of these resources. The immunomodulatory activity of the Bletilla species was assessed using the 3H-thymidine incorporation method test, and BSP-2 increased the pinocytic capacity and NO generation, which improved the immunomodulatory function[121,122].

    B. striata extract was shown to have anti-pulmonary fibrosis effect[123]. B. striata polysaccharide can successfully prevent lung fibrosis through established by invasive intratracheal instillation method and evaluated by lung indexes[123,124]. Moreover, Bletilla species need further investigations to evaluate their long-term in vivo and in vitro activity before proceeding to the development of pharmaceutical formulation.

    While there is currently a deep understanding of the pharmacological activity of plants in the Bletilla genus, there are still many gaps that need to be addressed. To overcome these shortcomings, future research on the pharmacological activity of Bletilla species should emphasize comprehensive, well-designed studies with a focus on species-specific effects, mechanistic insights, and rigorous clinical trials. Additionally, collaboration among researchers, standardization of methods, and transparent reporting of results can help advance our understanding of the therapeutic potential of Bletilla plants. Researchers should also consider safety aspects and explore potential herb-drug interactions to ensure the responsible use of Bletilla-based therapies.

    Application status and safety evaluation

    There are several common clinical applications of Bletilla striata in TCM. The gum of B. striata has unique viscosity characteristics and can be used as thickener, lubricant, emulsifier and moisturizer in the petroleum, food, medicine, and cosmetics industries[125−130]. B. striata is used as a coupling agent, plasma substitute, preparation adjuvant, food preservative and daily chemical raw material[131−133]. In clinical practice, B. striata glue has also been proven to control the infections and is beneficial to the healing of burns and wounds[133−135].

    In ethnic communities in Southwest China, the locals chew fresh Bletilla tubers directly or take them orally after soaking in honey to treat cough, pneumonia and other diseases[33, 34]. This traditional use is common in local communities in Southwest China, and suggests at the safety of Bletilla. However, current research shows it is still necessary to control the dosage when using Bletilla[136].

    Zebrafish embryos and larvae respond to most drugs in a manner similar to humans[137]. Militarine, the main active ingredient of Bletilla, was tested in a zebrafish embryo development assay at concentrations of 0.025 g/L and 0.05 g/L, and with the increased concentration, the heart rate of zebrafish embryos is slowed. Mortality and malformation rates of zebrafish embryos gradually increased with time and militarine concentration[138]. Although Bletilla species are safe at therapeutic dose ranges, further research on their safety is required[136]. More in-depth studies should be carried out on Bletilla to extract effective ingredients and make better preparations for clinical use[139].

    Conclusions and prospects

    According to the traditional medicinal knowledge in ancient Chinese texts, Bletilla has been an important ingredient for skin care since ancient times. Many ethnic minority groups in China still retain the practice of using Bletilla for skin care, and the plant parts and preparation methods of use are consistent with the records in ancient texts. Almost 300 phytochemicals have been identified from Bletilla, and some of them possess important pharmacological activities, which support its traditional uses and suggest the important medicinal development potential of this genus. This review has demonstrated that Bletilla, as an important medicinal plant of Orchidaceae, still requires further research to fathom its medicinal potential.

    For instance, it is necessary to enhance the quality control procedures based on the chemical components and pharmacological activity of Bletilla. The chemical composition and pharmacological properties of Bletilla are critical areas of current research. According to previous studies, the main bioactive components of Bletilla can vary greatly according to its origin, harvest time, distribution, storage, and adulteration. However, variation in bioactivities caused by the differences in Bletilla constituentshave not been explored extensively yet. To develop clinical applications of Bletilla, it is crucial to further explore the mechanism of action between its chemical composition variation and its pharmacological actions.

    In addition, although the tuber has historically been the main medicinal part of Bletilla, research has shown that the chemical composition in other parts of Bletilla, such as stems, leaves, and flowers, also give these parts a variety of pharmacological activities. Further in-depth analysis of the chemical components and pharmacological activities of different parts of this genus is worthwhile, to explore the specific chemical basis of its pharmacological activities, develop related drugs, and promote clinical applications. For example, Bletilla polysaccharide has good hemostasis and astringent wound effects[110], so it may have the potential to be developed into a drug or related medical materials to stop bleeding and heal wounds.

    Finally, as a cautionary note, many unrestrained collections and the destruction of habitats have made the resources of wild Bletilla rarer. In addition to protecting the wild populations of Bletilla, appropriate breeding techniques should be adopted to meet the commercial needs of this economically important genus, thereby allowing its sustainable use in commerce.

    Author contributions

    The authors confirm contribution to the paper as follows: study conception and design, funding acquirement: Long C; data analysis, draft manuscript preparation, literature review: Fan Y, Zhao J; manuscript revise and language editing: Wang M, Kennelly EJ, Long C. All authors reviewed the results and approved the final version of the manuscript.

    Data availability

    The raw data supporting the conclusion of this article will be made available by the authors, without undue reservation, to any qualified researcher. Requests to access these datasets should be directed to Yanxiao Fan (fanyanxiao0510@163.com).

    Acknowledgments

    This research was funded by the Yunnan Provincial Science and Technology Talent and Platform Plan (202305AF150121), Assessment of Edible & Medicinal Plant Diversity and Associated Traditional Knowledge in Gaoligong Mountains (GBP-2022-01), the National Natural Science Foundation of China (32370407, 31761143001 & 31870316), China Scholarship Council (202206390021), and the Minzu University of China (2020MDJC03, 2022ZDPY10 & 2023GJAQ09).

  • The authors declare that they have no conflict of interest.

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  • Cite this article

    Basunia A, Muttaqi A, Bhuiyan MRH, Badhon FA. 2024. Transportation mobility during COVID-19: a systematic review and bibliometric analysis. Digital Transportation and Safety 3(3): 169−183 doi: 10.48130/dts-0024-0015
    Basunia A, Muttaqi A, Bhuiyan MRH, Badhon FA. 2024. Transportation mobility during COVID-19: a systematic review and bibliometric analysis. Digital Transportation and Safety 3(3): 169−183 doi: 10.48130/dts-0024-0015
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Transportation mobility during COVID-19: a systematic review and bibliometric analysis

  • 1.

    Department of Civil and Environmental Engineering, Islamic University of Technology, Gazipur - 1704, Bangladesh

  • 2.

    Department of Civil and Resource Engineering, Dalhousie University, 5410 Spring Garden Road, Halifax, NS, B3H4R2, Canada

  • Received: 26 May 2024
  • Revised: 10 August 2024
  • Accepted: 22 August 2024
  • Published online: 30 September 2024
Digital Transportation and Safety  3,  2024, 3(3): 169−183  |  Cite this article

Abstract: The COVID-19 pandemic has significantly affected global transportation mobility, presenting unprecedented challenges to transportation management. Public transit and ride-hailing services saw a drastic reduction in ridership, leading to an increased inclination towards private vehicles. The pandemic also altered travel patterns and individual mobility due to various COVID-19 protocols. This study conducted a comprehensive review of 96 academic papers spanning from January 1, 2020, to December 31, 2022, focusing on transportation and mobility using the Scopus database. Three major themes were identified: 'Impact on Ride-Hailing Services', 'Impact on Mode Preference', and 'Impact on Trip Purpose', with subdivisions based on keywords and key findings extracted using VOSviewer. The pandemic significantly impacted ride-hailing services, altering demand, usage, and safety measures. Mode preference shifted towards private vehicles due to safety concerns. The present study underscores the long-term implications of the pandemic, emphasizing recovery strategies for ride-hailing services and mode preferences post-pandemic. It highlights the need for sustainable transportation policies, advocating for enhanced public transportation systems, promoting active travel modes, and addressing socioeconomic disparities in mobility patterns. The findings emphasize the need for resilient transportation strategies in the face of future disruptions.

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    Background

    • Transportation mobility around the globe was significantly hampered by the COVID-19 pandemic, which had unprecedented effects on various aspects of society, including social activities, the economy, and daily lives. This resulted in increased car ownership, inequalities due to unemployment and poverty worldwide. Furthermore, it was found that the ridership of public transit and ride-hailing services decreased by 70%−90% and 60%−70% respectively in major cities around the globe[1]. Hence, the shift towards private vehicles, and active modes of transportation was prominent[2,3]. For this reason, many operators, micro-mobility, and carpooling players halted their services during the pandemic, which directly affected the traditional automotive section that had projected 7.5 million fewer vehicles in 2020[4].

      In the early stages of COVID-19, people strongly responded to the threats imposed by the pandemic and avoided unnecessary travel, which led to the decline of all major transportation uses[5]. Again, the need for travel was noticeably reduced by encouraging work from home, distance education, job dismissals and abandonment of all social gatherings. Since these implications occurred in various phases of the pandemic, the deviations in travel patterns and transport mobility among the phases were prominent, specifically for commuting and social/recreational/leisure trips. In many countries, traffic was reduced dramatically across the weeks and during the lockdown period this volume declined significantly[6]. Therefore, the pandemic has immensely affected how people travel, their mindset, and their modal choices, including the use of private vehicles, public transportation, and active modes. This has also played a delicate role in advocating the decrease of environmental pollution from traveling.

      Although most studies were skewed toward traffic demand and mode choice modeling[7], the logical reasoning, and behavioral changes behind such outcomes and decisions were undermined. Therefore, a comprehensive literature review is crucial to delineate the current understanding and explorations associated with user behaviors in transportation mobility during and after COVID-19 in a global manner. Hence, this study aims to explore the literature gaps and point out behavior change, mobility changes, and their holistic impacts on different study themes through a rigorous literature review. The study has explored previous papers that focused on short-distance mobility and have refrained from long-distance mobility modes.

    Methodology

      Literature selection framework

    • The framework for this systematic literature review was prepared considering the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The primary search strategy focused on the keywords: COVID-19, mobility, and transportation. Boolean operators AND and OR were used to combine these keywords for a broader search scope. The study utilized literature from Scopus, a database indexing high-quality, peer-reviewed publications across various topics. The initial search yielded 1,037 articles.

      These articles were screened using the following exclusion criteria: only English-language publications from peer-reviewed journals published between January 1, 2020, and December 31, 2022, were included. Articles containing the keywords COVID-19, public transport, travel behavior, mobility, or their synonyms in the titles, abstracts, or reference lists were also included. All other articles were excluded. This screening process eliminated 562 articles, leaving 475 for further review.

      For the full-text analysis stage, an additional set of exclusion criteria was applied: studies outside the subject areas of social science, engineering, decision science, mathematics, and psychology were excluded. Additionally, irrelevant studies that did not align with the review scope based on title, abstract, key findings, or keyword review were excluded. This process resulted in the exclusion of 379 studies, leaving a final selection of 96 articles for the bibliometric analysis. The PRISMA diagram (2022) for this study is presented in Fig. 1.

      Figure 1. 

      The three-phased PRISMA (2022) diagram of the literature selection process.

      Theme and sub-theme selection

    • In the second phase, the three dominant themes were identified by using three distinct screening processes, which are as follows.

      Topic modelling

    • The first step analyzed the abstracts using topic modeling analysis in Python that generated a comparison diagram of the top 50 keywords and their frequencies (Fig. 2), providing the foundational understanding of the overall thematic landscape. This powerful tool is used in bibliographic analysis to uncover and identify thematic patterns.

      Figure 2. 

      Frequencies of the top 50 most used words in article abstracts.

      The Natural Language Toolkit's (NLTK) Punkt tokenizer was leveraged in Python for sentence splitting. Additionally, a stop word list was employed to clean the textual data from the 96 reviewed papers. Analyzing these high-frequency words provides a glimpse into the main topics discussed across the papers.

      For instance, words like 'public', 'mobility', 'changes', 'urban', and 'travel' appeared frequently. Interestingly, terms related to 'policies', 'sustainability', and 'green' were also used quite often. Notably, the prominence of words associated with 'change', 'sharing', and 'behavior' suggests a focus on public mobility and how urban behavior has changed. Additionally, words like 'transit', 'share', and 'system' indicate discussions on various modes of transportation, including mobility sharing and public transit systems. Similarly, the presence of terms like 'traffic', 'demand', and 'patterns' imply that traffic demand and patterns might have been analyzed for different modes of transportation.

      However, this preliminary analysis offers limited insights. To gain a deeper understanding of the thematic landscape, a Keyword Co-Occurrence analysis was conducted based on the keyword interpretations derived from topic modeling.

      Keyword co-occurrence diagram

    • Next, VOSviewer was employed, a text-mining tool, to conduct an in-depth analysis of the two-dimensional co-occurrence patterns of keywords (Fig. 3). Following this analysis, the keywords identified were simplified in the co-occurrence diagram by grouping them into three overarching themes based on their thematic dominance.

      Figure 3. 

      Keyword Co-Occurrence of 96 papers.

      Figure 3 depicts the co-occurrence of keywords extracted from the 96 reviewed papers, visualized using VOSviewer text mining software. The illustration reveals nine distinct research lines represented by nine colors.

      Thematic analysis of research lines:

      (1) Light blue cluster: This cluster, with the largest area, focuses on the impact of COVID-19 on travel behavior, specifically its effects on micro-mobility, trip purpose, and public transportation.

      (2) Dark blue cluster: While this cluster also touches upon the impact of COVID-19, it has a more specific focus on public transportation. It likely explores the pandemic's unique effects on ridership, service provision, and potential changes within public transportation systems.

      (3) Straw-colored cluster: This cluster explores the relationship between travel behavior changes and broader transportation trends. It examines the influence of travel behavior on public perception shared mobility adoption, and sustainable transportation.

      (4) Green cluster: This cluster investigates the interplay between the pandemic, travel behavior modifications, and transportation policies. It focuses on the pandemic's impact on travel behavior, the resulting traffic congestion patterns, and the effectiveness of lockdown policies.

      (5) Orange cluster: This cluster focuses on the impact of telework and equity on mobility.

      (6) Purple cluster: This cluster explores research related to shared urban mobility during the pandemic.

      (7) Pink cluster: This cluster investigates primarily public transit and congestion.

      (8) Brown cluster: This cluster examines the topic of transport policies.

      (9) Red cluster: This cluster focuses on human mobility habits and their relationship with smartphones.

      While the VOSviewer analysis identifies nine research lines, these can be logically grouped into three overarching themes based on their focus. These are:

      (1) Impact on ride-hailing services

      The light blue, red, straw, and purple clusters touch upon aspects of ride-hailing services (depending on the specific studies within those clusters), their impact on the mobility and change in behavior.

      (2) Impact on mode preference

      This theme could potentially encompass the light blue, dark blue, purple, straw-colored, and pink clusters. These clusters explore various aspects of travel mode selection including:

      • Impact of COVID-19 on public transportation use (light blue, dark blue)

      • Shared mobility options during the pandemic (purple)

      • Influence of travel behavior changes on mode preferences (straw-colored)

      • Public transit and congestion patterns (pink)

      (3) Impact on trip purpose

      This theme could potentially encompass the light blue, green, orange, and brown clusters. These clusters explore the reasons behind travel choices during the pandemic:

      • Impact of COVID-19 on trip purposes (light blue)

      • Travel behavior changes and their link to trip purposes (green)

      • Impact of telework arrangements on travel needs (orange)

      • Effectiveness of transport policies on trip purposes (brown)

      • Impact of mobility habits due to COVID-19 (red)

      This thematic grouping provides a more structured understanding of the diverse research directions. However, it's important to acknowledge that automated analysis using VOSviewer may not perfectly capture the nuances of each study. To address this limitation, manual screening was employed as an additional step.

      Manual screening

    • In the third phase, four reviewers (the authors) manually screened and verified the three themes based on key findings, research objectives, and abstracts of the 96 selected articles (as depicted in Table 1). This manual verification process helps ensure the accuracy and robustness of the thematic grouping.

      Table 1.  Theme considerations of keywords from different colored clusters.

      Keywords of different colored clusters (Fig. 3) Theme considerations after manual checking
      Telework Impact on Ride Hailing Services:
      In this theme, keywords and topics related to shared modes of transport, ride hailing services obtained via smartphone/tele networks, sustainable transportations used in ride hailing services and smart mobility options were considered.
      Bike sharing
      Transport policy
      Sustainable transportation
      Smart mobility
      Smartphone
      Shared mobility
      Sustainability
      Micro mobility Impact on Mode Preference:
      In this theme, keywords and topics related to different types of modes like public transportation, micromobility options, motorized mobility and mobility habits and choices that affected mode choices were considered.
      Public transit
      Transit
      Mode choice
      Mobility habits
      Public transportation
      Public transport
      Trip purpose Impact on Trip Purpose:
      In this theme, keywords and topics related to travel behavior and public perceptions regarding mobility that affected trip purpose were considered. In addition, the effect of traffic congestion was also taken into account.
      Traffic congestion
      Travel behavior
      Public perceptions
      Urban mobility Common Themes/Search Terms:
      COVID-19 and its synonyms used throughout different literature were taken into consideration. For mobility, its synonyms were also considered.
      Human mobility
      Mobility
      Pandemic
      Lockdown
      Covid-19
      Corona virus
      Transportation
      Sars Cov-2
      Covid-19 pandemic
      Equity Other Items:
      These keywords came out as prominent in different literature.
      Transportation justice
      Machine learning
      Latent class cluster analysis

      After identifying the three themes, they were further subdivided into sub-themes through manual screening by reviewers. Subsequently, the selected articles were assigned to the themes and sub-themes, considering and presenting any overlapping themes in Table 2.

      Table 2.  Theme and sub-theme distribution of reviewed literature.

      Major theme Ref. Sub-theme Keywords
      Impact on Ride
      Hailing Services      		 [9−31]

      Overlapped with Major Theme: Impact on Mode Preference − [46, 49, 51]

      Overlapped with Major Theme: Impact on Trip
      Purpose − [69, 97]      		 Change of Demand and Usage Anthropogenic air pollution, autonomous public transport, autonomous vehicles, bicycles, bike sharing, bike sharing system, car use, COVID-19, case studies, demand responsive transport, diseases, disease prevention, emerging mobility, epidemic and pandemic, human and behavioral factors, information and communications technology (ICT), instrumental variables, literature review, modal shift dynamics, ordinal logistic regression, public transportation, public transport, ridership, safety perceptions, Seoul, sharing anxiety, smart cities, smart city, social factors, transportation demand, transportation policy, travel behavior, travel characteristics, urban form, urban mobility, urban planning
      Rise of
      Micromobility      		 Active travel, bike sharing system, causal inference, cycling, COVID-19, e-scooter sharing system, food purchases, transportation means, spatial coupling, travel behavior, Saudi Arabia, spatiotemporal mean, user perception, lockdown, lockdown citi bike usage, urban greenway, micro-mobility, infrastructure intervention, mobility-as-service, natural experiment, yellow taxi demand, propensity score regression discontinuity
      Shift in service offering and safety measures Accident, car sharing usage, China, COVID-19, discrete choice modeling, generalized regret minimization, Heckman modeling, lockdown, ordered logit model, pandemic times, perception of risk, post-COVID-19 travel behavior, post-COVID-19 mobility public transport, random regret minimization, random utility maximization, ride-sourcing, road safety, shared mobility, sharing mobility, smartphone, sustainability, transport equity, travel behavior, travel mode choice, urban infrastructure, urban mobility, factor analysis, bike sharing motivations, perceived accessibility, sustainable transportation
      Socioeconomic Disparities Causal inference, coronavirus, COVID-19, COVID-19 effects, demand forecasting, discriminative pattern mining, health impacts, high-speed rail, instrumental variables, interpersonal distancing, mobility habits, mobility, multimodality, order-preserving traffic dynamics, public transport, recovery, ride-sharing, smartphone, suburban rail services, sustainable mobility, train capacity, transport equity, transportation, transportation planning, perceived accessibility, public transportation, lifestyle, teleworking, residential location
      Impact on Mode Preference [1−3,8,32−68]

      Overlapped with Major Theme: Impact on Ride
      Hailing Services −
      [10, 12, 17, 21, 29, 31]

      Overlapped with Major Theme: Impact on Trip
      Purpose − [71, 76, 86, 87, 95]
      		 Personal Vehicles Active travel, anthropogenic air pollution, bluetooth traffic monitoring system, COVID-19, disease prevention, equity, generalized linear mixed effects mode, Google and Apple mobility data, greenhouse gas emissions, healthy cities, Indian cities, mobile device data, mobility, mobility-shift, multi-disciplinary, post-pandemic, prediction, public transport, resilient public transport, smart card data, smart mobility, transport modes, transport policy India, transportation demand, travel behavior, travel modes, university students, transportation, travel behavior, modal share, level of urbanization, lockdown, Slovenia
      Towards Public Transportation and Shared mobility Bicycles, big data analysis, bike sharing motivations, bike-sharing system, biking Barcelona, Bluetooth traffic monitoring system, capacity management, case studies, case study, commuting, coronavirus, COVID-19, diseases, dockless bike-share system, emergency, epidemic and pandemic, factor analysis, food purchases, health impacts, homelessness, human and behavioral factors, inequality, infection fear, lockdown, lockdown CITI bike usage, longitudinal case study, mixed methods, mobility, mobility behavior, mobility change, mobility habits, mode shift, new normal, pandemic, prediction, probabilistic machine learning, propensity score regression discontinuity, public perceptions, public transit, public transport, public transport networks, public transport planning, public transportation, quasi-experimental research, recovery period, resilient transport systems, ridership, rural areas, safety-and-mobility trade-off, sars-cov-2, Seoul, smart card data, smart mobility, social distancing, social equity, social factors, spatial compartmental model, spatial coupling, spatiotemporal, sustainability, sustainable, sustainable mobility, tactical urbanism, teleworking, transit, transport and mobility related inequalities, transport and society, transport policy, transportation, transportation justice, transportation means, transportation planning, travel behavior, urban mobility, work from home, yellow taxi demand, Air quality index, COVID-19 response
      Active Transportation Activity-travel, best-worst scaling, bike-sharing system, biking Barcelona, built environment, central businesses district (CBD), corona, COVID-19, daily commuting, discrete choice, equity, generalized linear mixed effects mode, google and apple mobility data, google mobility report, Indian cities, mobile device data, mobility, modal choice, mode choice, pandemic, passenger transport, person-miles traveled, policy, probabilistic machine learning, public transport, quasi-experimental research, smart city, social impact, structural equation modeling, sustainability, sustainable mobility, tactical urbanism, telecommuting, traffic psychology, transport, transport policy, travel behavior, travel modes, urban mobility, urban planning, working from home, active travel, bike sharing
      Impact on Trip Purpose [69−97]
      Overlapped with Major Theme: Impact on Ride
      Hailing Services − [20]

      Overlapped with Major Theme: Impact on Mode Preference −
      [34, 37, 55, 65, 67]      		 Mode Choice on
      Trip Purpose      		 Activity-travel, activity chain, adaptive travel behavior, Americans with disabilities act (ADA), best-worst scaling, bike sharing systems, car use, causal inference, city periphery, COVID-19, covid-19 effects, COVID-19 strategies, disabled people activities of daily community, discrete choice, discrete choice model, disruptive events, dynamic CGE model, everyday leisure travel, GBDT model, global south, google mobility report, households, hurdle model, intercity bus transport, level of urbanization, lifestyle, lockdown, mobility, mobility patterns under epidemic modal choice, modal share, modal shift dynamics, modal split, non-mandatory activities, older adult, pandemic, paratransit, passenger transport services, people with disabilities, person-miles traveled, policy evaluation, public perceptions, public transit, public transport, public transport networks, public transportation, recovery period, recovery scenarios, residential location, ride-sharing, risk, safety perceptions, service contracting, service quality, Slovenia, social and recreational trips, social distancing, structural equation modeling, sustainable transport, sustainable transportation, telecommuting, teleworking, time-varying, transit, transport, transport and society, transport behavior, transportation equity, travel behavior
      Behavioral and Socioeconomic Effects Activity space, attitude towards teleworking, auctioning, coronavirus, commuting, COVID-19, daily commuting, demand management, equity, greater bay area (GBA), inequality, inflow control, latent class cluster analysis, mobile phone data, mobility, mobility habits, mode choice, movement control order, o–d flow, pandemic, pricing, public transit, public transport, public transportation, recovery, shopping, shopping trips, social exclusion, social inequity, spatial interaction, sustainable mobility, sustainable mobility, teleworking behavior, tradeable permit schemes, train travelers, transportation, travel behavior, travel frequency, travel patterns, trip purpose, work-based trips

      Finally, comprehensive review techniques like keyword extraction, key finding analysis, method analysis, etc. were employed to analyze various bibliographic features of the 96 reviewed articles. These features included location (country), study methodology, research timeline, trip purpose, analyzed modes, mode preference, and socioeconomic factors. Word cloud diagrams for the top 50 words were also used to show how the different literature revolved around certain keywords.

      Full-text analysis of the selected literature was then conducted to examine the impact, trends, and behavioral factors influencing transportation mobility within the three identified themes. This analysis also aimed to identify potential recommendations and research gaps. The workflow of the research is presented in Fig. 4.

      Figure 4. 

      Research workflow.

    Results

      Bibliometric features

    • The selected 96 articles were published in 36 reputed peer-reviewed journals, where the top three journals were Transport Policy with 21 publications, Sustainability with 13 publications, and Transportation Research Part A: Policy and Practice with 10 publications. All the journal articles are presented in Fig. 5.

      Figure 5. 

      Articles from different journals considered for detailed review and analysis.

      Among the 475 primary selected papers, 96 papers from 36 academic journals were retained for systematic literature review. 69.8% of the papers conducted research during 2021, followed by 2022, and the least number of papers during 2020. This pattern coincides with the fact that by 2021, the pandemic had its highest infection rate and this started to decrease during 2022[1]. Unfortunately, 216 countries or territories were affected by this disease. Subsequently, in the 96 papers, research was conducted in 35 countries, where the USA was one of the most affected countries, showing the highest numbers of research (16 papers), followed by Spain (seven papers) and India (six papers) in second and third positions respectively. Again, eight papers focused on worldwide coverage, while five concentrated on Europe and other selected countries since lockdowns in countries globally started in March 2020 (except China) owing to the uncontrolled outbreak (Fig. 6). The distribution of papers in different countries around the globe is illustrated in Fig. 7.

      Figure 6. 

      Lockdown initiation date and origin location of the analyzed articles.

      Figure 7. 

      Distribution of countries based on research location (highlighting the top 10 countries).

      This dispersal was further analyzed through a Sankey diagram (Fig. 8) to illustrate the distribution of the selected papers across different countries and highlighting their contribution to each focal theme (Table 2). The size and position of the Sankey's segments correspond to the number and significance of papers from each country, where the USA had a key contribution in all the focal themes, followed by Canada and Spain. However, India, Switzerland, Iran, and Sweden, among others, lacked the ride-hailing theme. Furthermore, other countries focused on either a single theme that had a physical effect on their society or was expected to have a foreshadowing effect soon.

      Figure 8. 

      Sankey diagram showing country of origin of the articles from three focal themes.

      Interestingly, 44.8% of the papers were either interviews, survey-based, or hybrid, whereas the rest of the papers used secondary data for their analysis. In the interview/survey-based papers, 31 pieces of literature collected their data online, and only nine papers physically considered the pandemic situation. Web-based interviews/surveys usually provide a wide range of convenience and respondents even in distant places. However, this could serve as the nesting ground for various biases, including self-reporting and response and non-response biases[8], which decreased the accuracy of the analysis. On the other hand, all these papers conducted their research through general evaluation of reports (highest), model building, standard statistical analysis, case study, and literature reviews presented in Fig. 9.

      Figure 9. 

      Analysis methodology adopted across 96 articles.

      Out of the 96 papers analyzed, 12 did not mention or analyze any specific transport mode and they discussed mobility in general. The remaining 84 papers focused on various transport modes, collecting and analyzing primary and/or secondary data. Public Transport Systems (PTS) were the most frequently analyzed, mentioned in 59 papers. Private transport was the subject of 35 papers, while both Road Safety Systems (RSS) and pedestrian transport (Foot) were covered in 27 papers, each. Cycle transportation appeared in 25 papers, and motorcycle transport was discussed in nine papers. Less frequently analyzed modes included paratransit and air, each mentioned in three papers, and micro transit, which was the focus of only one paper. Fifty-three papers discussed more than one mode to form a comparison. This distribution indicates the diverse range of research interests and the varying emphasis placed on different transport modes. A graphical representation of this is shown in Fig. 10.

      Figure 10. 

      Number of papers mentioning the listed transportation modes.

      A word cloud with the top 50 words from keyword analysis depicts the intensity and dynamicity of keywords (Fig. 11), to which indicates the studies mostly revolve around the keywords mobility, public, transport, covid, travel change, research, etc.

      Figure 11. 

      Word cloud with the top 50 words from keyword analysis.

      Impact on ride-hailing services

      Changes in demand and usage and the rise of micro mobility

    • Shared-micro mobility services surged in demand to facilitate a disease-resilient transportation system during the pandemic. A study in Singapore found that the total ridership increased by 150%, suggesting that the bike-sharing systems were an important alternative when public transit services became restricted[12]. Furthermore, in Karachi, Pakistan, individuals with more than two family members who traveled less than seven miles likely preferred carpooling[20]. Surprisingly, people with a higher net monthly income continued to generate more shared trips during this time in Dhaka, Bangladesh[13]. In Lisbon, Portugal there was an increase in bike sharing systems which became the most favored mode of mobility while public transport use decreased[69]. Unfortunately, sharing anxiety and willingness to share rides come as a major obstacle[22] in ride-sharing programs. For example, in Seoul, South Korea this decreased bike sharing and rentals drastically[21].

      During the pandemic, a study in India found that for public transit and sharing mobility, the demand dropped by 11% and 2% than the pre-pandemic time[98]. In Taipei and New Taipei of Taiwan there was a decrease in usage of metro and bicycle sharing between 8% and 18%, as well[46]. In Manhattan, USA the use of bicycle sharing was high and its demand surged more than yellow taxi system[51]. These findings correspond with study results that show public transport being the least preferred mode (Fig. 12). After the pandemic, there was a difference in travel demand recovery for different modes. For example, demand recovery was seen faster worldwide in private modes than in public transit or shared mobility[99].

      Figure 12. 

      Comparison between most preferred and least preferred transportation modes.

      Many of the studies were limited to the data from students[10], and many respondents had cultural differences, where herd behavior and personal space were not taken into account[22]. Limitations to demographic factors[19,30], and socioeconomic factors like high and low-income neighborhoods[31] decreased the accuracy of the models to predict behaviors and mode choice. Hence, factors like socioeconomic and psychological characteristics that affected user behavior in shared mobility went unnoticed in many cases.

      Shift in service offering and safety measures

    • As the impact of the pandemic started to diminish, service offerings in vehicles increased which improved the willingness to use vehicle-sharing services[14]. Users felt safer in this case and understanding user preference provided improved management in recovering demand[9]. For example, in Lisbon, Portugal before the COVID-19 pandemic the motivation to use bike sharing relied on personal well-being, service coverage and quality, this changed during the pandemic and the importance of public transport started to decrease[49]. In addition, a study in China found that travel mode choice shifted towards maximizing utility rather than fear of infection. There was an increase in using ride-hailing services for shopping and recreation activities in China, as well[25]. This might have happened due to the disruption created to the normal economy in China which suggests that individuals had to reassess their spending habits and divert to more cost-effective and convenient options to maximize utility. However, there was a willingness to pay between 19%−41% more for ride-sharing services depending on different trip purposes in Spain[14].

      However, these studies in many instances underrepresented populations, for example, respondents over age 65 referring to the elderly and lower-income households[11]. However, a study found that the disadvantaged group (elderly, low-income, and less tech-savvy people) had the disadvantage of accessible choice such as using virtual platforms and were forced to go outside to fend for daily and social necessities[24]. In addition, survey-based data might be highly conditioned by traumatic experiences that have been caused by socioeconomic uncertainty and health concerns[8]. Hence, further research considering this underrepresented group can be in understanding their ride-hailing services can be done in this regard.

      Socioeconomic disparities

    • Along with increased public transit trips, there was a sturdy growth in the number of COVID-19 cases, which indicated a cause-effect relationship[17]. In another study, it was found that the impact of COVID-19 on public transportation at stations situated outside Lisbon municipality and in lower-income zones was lower[23]. This might have happened as areas outside the municipality have fewer users of public transportation and people in lower-income zones were forced to use active modes like walking and cycling. Interestingly a study suggested that cost and convenience which played a crucial role in the mode choice decision was slowly being replaced by the risk of getting infected through different modes which in turn hinted to the increased demand for private modes and active modes of transport[97]. Since higher-income people had alternatives to this type of sharing service, they were exempt from using ride hailing services. In China, during this period, experienced older drivers who were active in duty and were highly respected depended more on ride-sharing services to make a living[18].

      Policy implications based on these studies had specific limitations, for example, lacks causation insights and is limited to an ordinal variable[26]. Artificial intelligence and urban computing get easily influenced by data bias and data transparency[23], raising ethical issues. Overall, studies never explored the long-term effect and recovery strategies for ride-hailing services in a post-pandemic scenario.

      Impact on mode preference

      Personal vehicle preference

    • The demand for bikes, private cars, and public transportation trips gradually changed in popularity with the increased health concerns during the pandemic[21]. Because of the lockdown, web-based activities substituted many of these trips[29]. Many people quickly rehabilitated their preferences from public and shared means to foot and private vehicles when the infection rates got worse[10]. For example, in Slovenia when commuting was reduced significantly due to lockdown, private modes like cars remained the main choice of travel, especially in rural areas[95]. Also, in Taipei, Taiwan, there was an increase in motor vehicle ridership[46]. This might have been because of factors like reduced exposure risk, avoidance of crowded spaces, and safe mobility. However, a study in Fuenlabrada, Spain contradicts this as private mobility decreased to 86% of their pre-COVID demand during the pandemic and made a faster recovery than public mobility which decreased to 94% of its pre-COVID-19 demand[48]. A finding in India found that for work trips, share for private modes and non-motorized transport were 10% and 4% higher among respondents after the COVID situation relaxed[100]. Preference for individual modes of transportation in China increased by 8.7%, whereas shared transportation modes decreased by 12%[25]. Similarly, in Greece, the use of public transportation services decreased significantly, dropping from 3.85 times per week to 0.69 times per week[39]. Again, Fig. 12 demonstrates that individual modes like private vehicles, motor bikes, bicycles, walking, etc. were preferred most.

      These findings indicate factors like socioeconomic stability and healthy safety perception play major roles in choosing modes. Notably, in some studies, lower-income people with limited access to the web and modern devices were underrepresented[1,31,44,86]. Furthermore, other studies had limited sample sizes that had spatial and temporal limitations[47,48], and few focused on students only[10,41]. In addition, processes like generalized linear mixed-effects[3] and regression models[1,44,55] being suitable for hierarchical data accounted for random effects of mobility due to COVID. Similarly, Gaussian Process Regressors[48] require a relatively large amount of data to effectively model complex relationships. These methods were employed by utilizing underrepresented lower-income groups and the socioeconomic stability of users, which is a recurring practice in many of the studies under this theme.

      Towards public transportation and shared mobility

    • The pandemic situation highlighted the vulnerability of local public transit and the perception of safety[60]. During the pandemic, public transportation usage in Turkey and Spain drastically decreased by 80%[64] and 95%[48] respectively. In addition, because of the lockdown, there was a higher willingness to telework which further decreased public transportation use[36]. However, public transit was a critical mobility option for the homeless or lower-income people[76]. In Washington, USA the lower-educated and lower-income people experienced declines in travel intensity, which affected their travel behavior even after the COVID period[54]. This solidifies the finding of this study that public transportation is the least preferred mode in most of the papers that discussed this topic (Fig. 12) but for people who have no other choice, public transportation played a significant role. However, many countries have already started to bounce back with predictions going for higher travel frequencies related to public transport[98]. Again, a study in Toronto, Canada observed a decrease in the usage frequency of ride-sourcing but a small percentage of respondents showcased an increased ride-sourcing usage, which might have attributed to the increased perseverance to avoid crowded spaces and public transit[11].

      Similarly, a study in Manhattan, USA found that the impact of the shared mobility system was higher than the yellow taxi system, and the demand surged during the pandemic[51]. In Daejeon, Korea, bike-sharing increased both during and after the pandemic[101]. However, a study in Barcelona revealed that the liking to bike sharing decreased during the pandemic[2], which is opposed to the study findings that found mobility sharing as one of the most preferred modes (Fig. 12). Then again, a study suggested that shared micro-mobility had the potential in the future to become a disease-resilient mode of transport[12]. This indicates that certain demographic, socioeconomic, and psychological factors address the choice of shared mobility, which needs to be focused on.

      Active mode of transportation

    • In North Carolina, USA, individuals preferred walking and driving over public transit during the pandemic[1]. On the other hand, a study in Dhaka, Bangladesh found that non-motorized vehicles were 19.93% more popular[10]. Again, in The Netherlands, measures that encouraged cycling and walking also scored positively[42]. However, in Greece, this effect varied for males and females as parameters like ecological footprint, safety measures, and personal safety mattered most for females. Cycling was more preferred there and 30% of their population already reduced car usage even after the pandemic[67]. In Spain, there was also a slight increase in the usage of active modes of transport[87]. In Shiraz, Iran, the average cycling and biking was still higher for Central Business District users after the pandemic[55].

      A similar case also occurred in many European countries as demand for active modes of transportation continued to increase after the pandemic[32]. These outcomes align with the findings of this study. Active modes of transportation are one of the most preferred modality choices (Fig. 12). However, the majority of the papers that discussed active modes of transportation relied on general evaluation and normal statistical analysis and had data limitations mentioned in the earlier themes. However factors that presented user behavior/personas were sometimes shadowed by traffic demand and policy mapping.

      Impact on trip purpose

      Mode choice on trip purpose

    • For rigorous classification, trip purposes were clustered into three distinct types: (1) Mandatory trips, (2) Maintenance trips, and (3) Discretionary trips[91]. At the start of the pandemic in Brazil, there was a substantial reduction in working (Mandatory trips) and non-essential (Discretionary trips) trips. Results indicated that essential workers were nearly three times more likely than the general population to make a mandatory trip during this time. Discretionary trips were more likely to be made by males in comparison to females[77]. Again, in Zurich, Switzerland, maintenance trips like park and grocery visits increased, while discretionary trips decreased during the lockdown period. This observation coincides with the findings of this paper that revealed the occurrence of Maintenance trips the most, with 12 papers focusing on this aspect.

      It is noteworthy that Mandatory trips experienced the most substantial decline during the COVID-19 pandemic. Findings of the study conducted by Rafiq et al.[71] and Pawar et al.[93] concluded that the severity of COVID-19 had a more pronounced impact on workplace visits during the pandemic, which also affected low-income workers. Discretionary trips had lower travel frequency by 92% in comparison to mandatory trips in India. The diverse choices made by users during the COVID-19 pandemic are presented in Fig. 13. In Seattle, USA mandatory trips like medical trips increased drastically and people from lower-income communities highly relied on paratransit[34].

      Figure 13. 

      Mode choice preference by percentage.

      Behavioral and socioeconomic effects

    • During the pandemic, discretionary trips were largely canceled due to lockdowns[78]. For people with disabilities, their daily travels were significantly reduced by destination[82]. However, older adults preferred active modes of transportation during and after the pandemic to avoid social constraints and crowds in their trips[55]. In the USA, transit riders with lower incomes had reduced their trips significantly[87]. In King County, Washington, USA people with lower education and lower income also reduced their travel significantly[55]. Again, in Toronto, Canada, people were reliant on private vehicles rather than public transit for non-mandatory trips[91]. Furthermore, there was a significant drop in trips based on travel purposes, infection, fear, occupation, and household[96]. In the USA, public transportation use among lower-income groups decreased by 32%, and among the general population, it declined by 51%[54]. These findings signify changes in travel behavior due to changes in socio-economic characteristics[55,65]. This greatly affects the purpose of trips for different demography of people during the COVID-19 pandemic.

    Discussion and conclusions

    • The objective of this research was to examine the alterations in transportation mobility and travel patterns due to the COVID-19 pandemic. Utilizing a systematic review and bibliometric analysis, 96 papers from the Scopus database were rigorously. These papers were categorized into three major themes: 'Impact on Ride-Hailing Services', 'Impact on Mode Preference', and 'Impact on Trip Purpose'. Text mining techniques were employed to extract key findings from each theme.

      The majority of the research works focused on the year 2021, corresponding with the pandemic's peak. Interestingly, a geographical correlation emerged between the severity of the outbreak and the location of the research. The USA dominated research output, followed by Spain and India. Notably, the USA consistently played a significant role across all themes, while some countries prioritized themes with direct societal impact, potentially reflecting resource limitations or immediate infrastructural needs. This research disparity highlights the need for a more balanced global perspective in future investigations. Increased research focus in regions with initially lower output is crucial for a comprehensive understanding of the pandemic's long-term effects on travel behavior.

      This systematic review identified a dominance of interview/survey-based research (44.8%), often relying on online data (31 papers), which can introduce bias. Future studies should prioritize data triangulation with on-ground surveys and travel data, alongside longitudinal approaches, to gain a more comprehensive picture. Future research should incorporate sensor-based data collection (e.g., travel time estimation from GPS data) and agent-based modeling to simulate travel behavior under different pandemic scenarios. This would allow engineers to test and refine infrastructure modifications and public transportation policies for optimal efficiency and user safety. Significant literature gaps exist in under-represented regions (minimal initial research) and for vulnerable populations, highlighting the need for broader regional coverage and a deeper understanding of the pandemic's impact on diverse demographics and the three themes: 'Impact on Ride-Hailing Services', 'Impact on Mode Preference', and 'Impact on Trip Purpose' of this paper.

      The COVID-19 pandemic exposed significant vulnerabilities in the shared mobility landscape, with ride-hailing services experiencing drastic shifts in demand, usage patterns, service offerings, and safety protocols. Shared-micro mobility also emerged as a crucial alternative during public transport restrictions, particularly in developing regions where usage surged[12], other areas witnessed declines due to concerns about shared surfaces and potential virus transmission. These contrasting trends highlight the multifaceted nature of user behavior in shared mobility and underscore the critical need for in-depth research on the psychological and behavioral factors influencing mode choice within this sector. The co-occurrence diagram of keywords also revealed prominent studies on the effect of travel behavior on shared mobility and sustainable transportation. Such research can be instrumental in developing targeted interventions to foster long-term sustainability for shared mobility models across diverse geographical and socio-economic contexts. In addition, research on the provision of flexible transportation strategies should be given emphasis to prepare for similar pandemic situations in the future.

      For sustainable urban development, multimodal transportation is advocated over reliance on a single mode, with telecommuting being an integral part of sustainable infrastructure strategies[7]. However, during the pandemic a concerning trend has emerged – a rise in private car usage documented across various studies[1,3,10,20,25,46,47,52,60,91,95,97]. Studies have consistently emphasized the importance of bolstering infrastructure for cycling, such as expanding and maintaining dedicated bike lanes and improving route quality and intersection safety for pedestrians[2,35,93]. Similarly, enhancements in walking infrastructure were recommended, focusing on route quality, intersection safety, and the incorporation of green spaces, which positively influence walking utility[35,93,83]. It is seen from above that many studies emphasized infrastructure and policy recommendations that promoted multimodal travel, particularly combinations with active transportation modes. This presents an opportunity for urban planning engineers to re-evaluate existing infrastructure. While the focus on sustainability is commendable, a gap exists in understanding commuter preferences for these combined trips. To address this gap, further research is necessary to explore commuter preferences and the various travel mode combinations they utilize, with a specific focus on informing the development of sustainable infrastructure.

      Public transportation usage by low-income groups persisted during the pandemic[23,34,37,39,40,54,76,77,86,91]. It was also found the modal share of public transportation drastically decreased to less than 10% according to certain authors[95,77]. These findings signify that public transportation systems were one of the least preferred modes of travel during the pandemic and this was the most frequently analyzed, mentioned in 59 papers. This highlights the need for targeted solutions and policy implementations to support these populations. Strategies such as contactless travel, e-tickets, and improved sanitation measures were recommended to mitigate the risk of infection and promote public transit use[41,43,50,67,74,83]. In addition, to better support this population, rigorous research is needed on solutions that promote safe and hygienic public transport travel.

      However, the uneven recovery rates between public transit/transport and private vehicles in different regions suggest a need for context-specific solutions. In areas with limited access to private vehicles, could investments in public transit infrastructure (e.g., improved ventilation systems) and real-time occupancy information displays entice riders back to public transportation? Engineering solutions could involve integrating real-time travel demand data from ride-hailing services with public transportation schedules to dynamically allocate resources during emergencies. Additionally, exploring partnerships between public and private transportation providers could lead to innovative micro transit solutions (e.g., demand-responsive buses) that cater to specific trip purposes and demographics during disruptions.

      Maintenance trips, though reduced, continued to occur during the pandemic. Effective management strategies, such as establishing outdoor sites near residences for daily necessities, were proposed to reduce the frequency of these trips and minimize infection risks[81]. Workplace trips saw the highest decline during the pandemic compared to non-workplace trips. For ride-sharing services, understanding customer willingness to pay more and considering economic factors in service cost calculations were highlighted[8,31]. It was found that customers were willing to pay upwards of 19% for better services[14]. Increasing the number of electric and cargo bikes was suggested to enhance service utility[2,35]. Surprisingly, different studies also talked about the effect on the differently abled population and their behavior shift in using different modes but they were few[82,34]. Among the 96 analyzed papers, 35 studies directly or indirectly addressed the factors influencing trip choice. This highlights the need for further research to analyze the direct and indirect factors influencing trip purpose, with a particular focus on the differently-abled population. Such research is crucial for understanding and addressing sudden changes in mobility behavior.

      In summary, this study synthesizes an extensive array of policies and recommendations, providing valuable insights into the multifaceted approaches adopted by governments and policymakers. While this research offers a comprehensive review of transportation mobility during the COVID-19 pandemic, it also provides recommendations and discusses the potential areas of focus considering future transport mobility. However, the study did not consider the extreme shifts in travel behavior at various pandemic stages and long-distance travel modes like air travel and sea travel. This needs to be addressed in future studies. Researchers should undertake a time-series analysis to evaluate how transportation mobility has evolved throughout the pandemic.

      In addition, the review process might have inadvertently favored published studies with statistically significant findings. Studies with null or negative results may not have been published, potentially skewing the overall interpretation of the data. To mitigate this, studies should include unpublished reports or grey literature (e.g., government reports, conference proceedings) in future reviews. The selection of keywords and databases used for the literature search could have limited the range of studies identified. However, this search bias was kept to a minimum by considering synonyms of the primary keywords and using Boolean operators such as AND and OR to combine the keywords. Selection bias was also reduced by utilizing pre-defined inclusion and exclusion criteria along with a rigorous screening process by four reviewers. By employing four reviewers with diverse perspectives, the influence of the reviewer's own biases on the interpretation and synthesis of the findings from the reviewed studies (also known as synthesis bias) was kept to a minimum.

    Author contributions

    • The authors confirm contribution to the paper as follows: study conception and design: Bhuiyan MRH; data collection: Basunia A, Muttaqi A, Bhuiyan MRH, Badhon FA; analysis and interpretation of results: Basunia A, Muttaqi A; draft manuscript preparation: Basunia A, Muttaqi A, Badhon FA, Bhuiyan MRH. All authors reviewed the results and approved the final version of the manuscript.

    Data availability

    • The data that support the findings of this study are available from the corresponding author, upon reasonable request.

      Conflict of interest

      • The authors declare that they have no conflict of interest.

      • # Authors contributed equally: Aditya Basunia, Azwad Muttaqi

      Rights and permissions
      • Copyright: © 2024 by the author(s). Published by Maximum Academic Press, Fayetteville, GA. This article is an open access article distributed under Creative Commons Attribution License (CC BY 4.0), visit https://creativecommons.org/licenses/by/4.0/.
    Figure (13)  Table (2) References (101)
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    Cite this article
    Basunia A, Muttaqi A, Bhuiyan MRH, Badhon FA. 2024. Transportation mobility during COVID-19: a systematic review and bibliometric analysis. Digital Transportation and Safety 3(3): 169−183 doi: 10.48130/dts-0024-0015
    Basunia A, Muttaqi A, Bhuiyan MRH, Badhon FA. 2024. Transportation mobility during COVID-19: a systematic review and bibliometric analysis. Digital Transportation and Safety 3(3): 169−183 doi: 10.48130/dts-0024-0015
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  • Background
  • Methodology

  • Literature selection framework

  • Theme and sub-theme selection

  • Topic modelling
  • Keyword co-occurrence diagram
  • Manual screening
  • Results

  • Bibliometric features

  • Impact on ride-hailing services

  • Changes in demand and usage and the rise of micro mobility
  • Shift in service offering and safety measures
  • Socioeconomic disparities

  • Impact on mode preference

  • Personal vehicle preference
  • Towards public transportation and shared mobility
  • Active mode of transportation

  • Impact on trip purpose

  • Mode choice on trip purpose
  • Behavioral and socioeconomic effects
  • Discussion and conclusions
  • Author contributions
  • Data availability
  • Conflict of interest
  • Rights and permissions
  • About this article
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