Evolution of scientific production on urban passenger transport: A bibliometric analysis

Verano-Tacoronte, Domingo; Flores-Ureba, Sandra; Mesa-Mendoza, Margarita; Llorente-Muñoz, Virginia Article Evolution of scientific production on urban passenger transport: A bibliometric analysis European Research on Management and Business Economics (ERMBE) Provided in Cooperation with: European Academy of Management and Business Economics (AEDEM), Vigo (Pontevedra) Suggested Citation: Verano-Tacoronte, Domingo; Flores-Ureba, Sandra; Mesa-Mendoza, Margarita; Llorente-Muñoz, Virginia (2024) : Evolution of scientific production on urban passenger transport: A bibliometric analysis, European Research on Management and Business Economics (ERMBE), ISSN 2444-8834, Elsevier, Amsterdam, Vol. 30, Iss. 1, pp. 1-16, https://doi.org/10.1016/j.iedeen.2023.100239 This Version is available at: https://hdl.handle.net/10419/294140 Standard-Nutzungsbedingungen: Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden. 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If the documents have been made available under an Open Content Licence (especially Creative Commons Licences), you may exercise further usage rights as specified in the indicated licence. https://creativecommons.org/licenses/by-nc-nd/4.0/ European Research on Management and Business Economics 30 (2024) 100239 Available online 12 January 2024 2444-8834/© 2023 The Author(s). Published by Elsevier España, S.L.U. on behalf of AEDEM. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Evolution of scientific production on urban passenger transport: A bibliometric analysis Domingo Verano-Tacoronte a , * , Sandra Flores-Ureba b , Margarita Mesa-Mendoza c , Virginia Llorente-Mu˜ noz d a Department of Economy and Bussiness Management, University of Las Palmas de Gran Canaria, Saulo Tor´ on, 4. 35017. Las Palmas de Gran Canaria, Spain b Department of Business Economics, Rey Juan Carlos University, Paseo de los Artillleros s/n., 28032. Vic´ alvaro, Madrid, Spain c Department of Financial Economics and Accounting, University of Las Palmas de Gran Canaria, Saulo Tor´ on, 4. 35017 Las Palmas de Gran Canaria. Spain d Department of Accounting and Management, University of Malaga, Calle El Ejido, 6. 29071 M´ alaga, Spain ARTICLE INFO JEL classification: R00 R41 R49 Keywords: Urban passenger transport Bibliometric analysis Scientific maps Longitudinal analysis ABSTRACT Urban passenger transport is a key point in the progress of any city. It is a strategic area whose efficient and sustainable development requires the incorporation of multiple disciplines. It affects territorial, social, health, economic, and environmental policies, among others. In recent years, we have witnessed a series of changes, especially in the domains of technology and environmental issues. The interdisciplinary nature of transport together with these developments has produced fundamental and far-reaching changes in the scientific production related to this field of study which is difficult to cover in a traditional review of the literature. The aim of this work is thus to conduct a bibliometric analysis of urban passenger transport during the period 2001–2021, which illustrates the advances made during this period and stimulate new research in this field. SciMAT software was used for this purpose. The results show the conceptual evolution of urban passenger transport research, identifying seven main thematic areas: (1) health and physical activity, (2) travel, (3) transport policy, (4) air pollution, (5) congestion, (6) social exclusion, and (7) electric and autonomous vehicles. 1. Introduction The efficient development of urban passenger transport (UPT) is a crucial aspect in urban mobility and sustainability (Lindkvist & Melander, 2022). One of the most studied aspects of UPT is a decrease in congestion in cities (Ewing et al., 2018; Tirachini et al., 2014). This is further associated with minimizing greenhouse gas emissions (Adams et al., 2020; Creutzig et al., 2015) and guaranteeing travel for a large part of the population (Saif et al., 2018; Shi et al., 2020). Overall, the operation and available forms of transportation affect the economic and social development of cities (Bastanchury-L´ opez & De-Pablos-Heredero, 2022; Ortega-Fern´ andez et al., 2020; Phillips et al., 2021). In recent years, the research and analysis of UPT systems has received a great degree of attention due to the many changes in the context in which it is embedded. These affect, fundamentally, the environmental (Heiskala et al., 2016; Okraszewska et al., 2018; Sharifi, 2021; Wołek et al., 2021; Zhao et al., 2020) and technological aspects (Golbabaei et al., 2021; Paddeu et al., 2020; Soteropoulos et al., 2019). From an environmental perspective, climate change has accelerated the development of policies aimed at mitigating and adapting to its effects in cities. These policies aim to: increase the efficiency of public transport (Song et al., 2016), encourage the withdrawal of (older) more polluting vehicles (Epicoco & Falagario, 2022; Mounce & Nelson, 2019), spur the search for more environmentally friendly fuels (Li et al., 2010; Wang & Lin, 2019), and reduce the use of private vehicles, replacing them with alternative forms of transport (e.g., bicycles, walking) (Pucher et al., 2011; Zhao & Li, 2017). The technological perspective relates to improving the attractiveness of existing modes and the emergence of new forms of transport (Sharifi, 2021; Webb, 2019). UPT is a complex and multifaceted issue encompassing several disciplines, including urban planning, transport engineering, environmental and social sciences, and public policy. The various perspectives from which it can be approached make it an important field of study. Its interdisciplinary nature, however, means that traditional literature reviews cannot cover the thematic diversity and large volume of scientific production on the subject (Sharifi, 2021). A bibliometric analysis counters these obstacles by offering tools that help analyze large quantities of publications (Cobo et al., 2011; Ji et al., 2023; Shen et al., * Corresponding author. E-mail address: [email protected] (D. Verano-Tacoronte). Contents lists available at ScienceDirect European research on management and business economics journal homepage: www.elsevier.es/ermbe https://doi.org/10.1016/j.iedeen.2023.100239 Received 20 July 2023; Received in revised form 18 December 2023; Accepted 19 December 2023 European Research on Management and Business Economics 30 (2024) 100239 2 2023). It allows us to examine metrics related to the performance of different elements, including authors, universities, journals, and countries. Furthermore, it can map the structure of research in a given field (Ji et al., 2023), thereby illustrating the evolution of the topics in which research is conducted and allowing us to explore the interrelationships between different subfields (Cobo et al., 2011). Based on the large body of research carried out between 2001 and 2021, this article will synthesize and analyze the most significant contributions made in the field of urban passenger transport through the analysis of their temporal evolution. This is done via a bibliometric analysis using the SciMAT tool. The broad scope of this topic has led different researchers to conduct bibliographic and bibliometric analyses, generally focused on specific areas. These areas include, for example, sustainable transportation (Sharifi, 2021), accessibility (Saif et al., 2018; Shi et al., 2020), safety (Shen et al., 2023), or smart mobility (Abduljabbar & Dia, 2022; Ji et al., 2023). This work provides a comprehensive study of the multiple thematic areas relating to the development of UPT activity (i.e., health, technology, business management, environment, urban planning). This allows us to examine the interrelationships between the different concepts and approach UPT from an integrative perspective. Likewise, the volume of research and the broad time frame covered in this study provide a complete perspective of the state of UPT research and the different stages that have led to this point. The results show how key trends in transportation research, as well as emerging methodologies and results, have grown at a rapid pace in recent years. Seven major thematic areas are highlighted: health/physical activity, travel, transport policy, air pollution, congestion, socialexclusion, and electric vehicles. To this end, this paper first analyzes the theoretical framework of UPT. Then follows an explanation of the methodology required to conduct the work, both in terms of the database from which the scientific publications were extracted and the bibliometric tool used for their analysis. Next, the results are presented, and finally, the most relevant conclusions are pointed out. 2. Theoretical framework Transportation is tied to the economic and social development of cities; it facilitates the growth of the economy and the movement of people and goods, thereby improving overall quality of life (Chatziioannou et al., 2023; Kim et al., 2020; Phillips et al., 2021; Politis et al., 2021; Saif et al., 2018). However, some transportation-related factors may compromise the quality of life in cities. Consider the use of private vehicles, deemed the greatest contributor of polluting gases and largest consumer of energy (Epicoco & Falagario, 2022; Zhao et al., 2020) together with the estimation that by 2050, 68 % of the population will be living in urban areas (Allam & Sharifi, 2022; L´ opez et al., 2019). The high population density coupled with unequal growth between different modes of transport (with road transport and specifically private vehicles given priority) can diminish the quality of life for many (Adams et al., 2020; Bastanchury-L´ opez & De-Pablos-Heredero, 2022). Efficient urban passenger transport boasts many benefits: it supports urban mobility and sustainability (Lindkvist & Melander, 2022), facilitates accessibility to jobs or leisure, favors social and territorial equity, reduces congestion, minimizes environmental impact, and optimizes the use of healthy resources (Adams et al., 2020; G´ omez-Ortega et al., 2023; Kim et al., 2020; Lopes Toledo & L` ebre La Rovere, 2018; Oviedo & Attard, 2022). Achieving an efficient transportation system is associated with the improvement of public transportation (Das et al., 2021; Song et al., 2016) and reduction in the use of private vehicles, replacing these with alternative forms of transport (e.g., bicycles, walking, electric vehicles). The use of technology that benefits the passenger is also beginning to gain importance (Nehk et al., 2021; Pucher et al., 2011). These actions are proposed to adapt to more sustainable mobility and the changes in mobility of new generations (Delbosc & Currie, 2013) by promoting mobility as a service (Mobility as a Service - MaaS) (Alyavina et al., 2020; Lindkvist & Melander, 2022). Improving urban passenger transport, however, involves the integration of several different disciplines, such as urban planning, transportation engineering, environmental and social sciences, and public policy implementation (Allam & Sharifi, 2022; Barnett et al., 2017; Bordagaray et al., 2014; Chatterjee et al., 2020; Epicoco & Falagario, 2022; Oviedo & Attard, 2022; Song et al., 2016). With these guidelines, public policies aimed at achieving more efficient transport are marked in the agendas of governments worldwide. This follows the publication of documents such as “Cities on the move. A World Bank Urban Transport Strategy Review” (World Bank, 2002). The purpose of this report was to analyze the problems of urban transport, articulate strategies to improve it, and identify the role of the World Bank in contributing. Agreements such as those reached at the “World Summit on Sustainable Development” (United Nations, 2002) were signed by countries committed to include measures to improve the environment, giving a priority role to the development of policies to improve public transport. Additionally, the implementation of the Kyoto Protocol in 2005 underscored the need and urgency to limit the greenhouse effect linked to transport. During this period, the European Union assumed an important role through the measures set out in the White Paper “European Transport Policy for 2010: Time to Decide" (European Commission, 2001). These measures achieved great progress in transport, but even so, were unable to solve problems of transport sustainability. The Commission therefore proposed the need to define lines of action to achieve sustainability in transport. The White Paper "Roadmap to a single European transport area: towards a competitive and sustainable transport policy" (European Commission, 2011) was published to guide the transportation policies of the member countries and impact the decisions adopted by international organizations. In parallel, “The World Bank Annual Report 2010: Year in Review” (World Bank, 2010) was published to highlight the development of sustainable transportation measures to mitigate the greenhouse effect problems. With the importance of reducing harmful gas emissions and decreasing dependence on fossil fuels gaining international relevance, the publication of the 2030 Agenda (United Nations, 2015) and the signature of the Paris Agreement (United Nations, 2015), have marked the commitment of most countries to address the environmental, social, and economic challenges caused by climate change. In 2020, the Covid-19 pandemic provided a portrait of the impact of displacement, as the near paralysis of economic activity managed to slow climate change and brought about greater awareness on the part of individuals (Allam & Sharifi, 2022; Barbieri et al., 2021; Beck & Hensher, 2020; Das et al., 2021). Given the significance of these milestones, they will be taken into account for the longitudinal analysis of results by periods. 3. Methodology The path to cover the objectives of this work is carried out in two steps: first, we identify the set of publications in the field of study, and second, we configure the bibliometric map that monitors urban passenger transport. The purpose of scientific maps as a bibliometric technique is to illustrate the structure and evolution of the field of scientific research (Alhjouj et al., 2022; Braam et al., 1991a, 1991b; Cobo et al., 2011) These are applied longitudinally in order to understand the evolution of the research field throughout the study period. 3.1. Database The search for publications is conducted in the Web of Science (WoS) Core Collection database, as it feeds the Journal Citation Reports (JCR) D. Verano-Tacoronte et al. European Research on Management and Business Economics 30 (2024) 100239 3 to establish the impact factor that gives prestige to scientific journals (Paule-Vianez et al., 2020). In addition, this database includes journals with a high impact factor also found in other databases (such as Scopus). In line with this, there are multiple bibliometric analysis studies in different areas of knowledge (Bastanchury-L´ opez & De-Pablos-Heredero, 2022; Ellegaard & Wallin, 2015; Merig´ o & Yang, 2017; Paule-- Vianez et al., 2020; Sharifi, 2021; Zhao et al., 2020). From this database, the Social Sciences Citation index is selected, as it holds JCR articles from the field of Social Sciences. With this selection, commonly used for bibliometric studies in the field of management (Bastanchury-L´ opez & De-Pablos-Heredero, 2022), the intention of the work is to monitor topics of interest from the field of social science research. The search, carried out on September 9, 2022, covers the period of analysis from 1/1/2001 to 12/31/2021, focusing on the analysis of the evolution of publications on urban passenger transport in the 21st century. For this period, an advanced search with the criteria "urban transport," "public transport," or "passenger transport" was carried out, yielding a total of 7456 bibliographic outputs. This yield was further refined by choosing publications categorized as articles, review articles, early access, and editorial materials. Following this, the sample to start the bibliometric analysis and monitor research in the field of study was configured by 6920 references for the selected period, which were exported to the SciMAT tool. 3.2. SciMAT analysis The SciMAT tool is used to analyze the thematic and conceptual evolution of the field of study. Of the various options for conducting bibliometric studies, this software is chosen for its flexibility in selecting measures to generate and visualize bibliometric networks, as well as for the various techniques that allow debugging of the database as input to the analysis process (Paule-Vianez et al., 2020). The possibility that the research outputs comprising the database exported to SciMAT may be insignificant, duplicated, or contain errors is mitigated by the tool’s capacity for an adequate filtering process. This enables the monitoring of a higher quality database. In recent years, this software has been applied in multiple works analyzing different areas, such as finance (Alc´ azar-Blanco et al., 2021; Paule-Vianez et al., 2020), road safety (Ji et al., 2023), autonomous vehicles (Morooka et al., 2023), and sustainable transport (Sharifi, 2021). The methodological process in SciMAT begins by choosing the unit of analysis that is the reference point for studying the research field to be analyzed. Of the different possible options, the "keywords" are chosen, since the focus is on more conceptual aspects of the research area (Cobo et al., 2012). A clustering process is performed to locate groups of keywords based on a co-occurrence analysis, considering such a relationship will exist between words when they appear together in documents in the database (Alhjouj et al., 2022). For the clustering algorithm used to extract the main themes, the simple center algorithm is chosen. In addition, the h-index (Alonso et al., 2009; Cobo et al., 2012), the total number of publications, and total number of citations are selected as quality measures (Paule-Vianez et al., 2020). Fig. 1 shows the bibliometric outputs to be analyzed: a) the strategic diagram, b) the thematic network, c) the thematic area evolution map, Fig. 1. Outputs of bibliometric analysis. Source: Cobo et al. (2011); Sharifi (2021) D. Verano-Tacoronte et al. European Research on Management and Business Economics 30 (2024) 100239 4 and d) the overlay graph. The strategic diagram represents the research topics on a Cartesian map based on two measures that characterize each topic: density and centrality. Density measures the internal strength of the network, i.e., the internal cohesion of a topic, while centrality expresses a network’s degree of interaction with respect to other networks (Callon et al., 1991; Cobo et al., 2011; Sharifi, 2021). Both measures are used to classify themes into one of four categories: driving themes, basic and cross-cutting themes, highly developed themes, and emerging or disappearing themes. The driving themes of the research field are in the strongest quadrant of centrality and density, giving rise to themes that are well developed and important to the research field. The opposite quadrant, low centrality and density, includes underdeveloped and marginal topics, giving rise to emerging or disappearing topics. Basic or cross-cutting topics, with high centrality but low density, are topics which relate to the rest but are poorly developed in themselves. Finally, highly specialized themes are themes with low centrality but high density, being highly developed but not as connected with the rest (Alc´ azar-Blanco et al., 2021; Callon et al., 1991; Cobo et al., 2011; Sharifi, 2021) As pointed out by Sharifi (2021), the thematic network complements the strategic diagram. In it, each topic is represented by a network with its nodes (keywords). The size of the sphere of each node is proportional to the number of documents associated with that keyword, and the thickness of the line between two nodes is proportional to its equivalence index (Cobo et al., 2011). To show the evolution of the thematic areas in the field of research throughout the study period, the evolutionary bibliometric map is analyzed. This shows the different thematic areas, represented with different shading (Fig. 1). A thematic area or thematic line is defined as a group of topics that have evolved over several consecutive periods of time (Cobo et al., 2012). In this map, the size of the nodes is directly proportional to the number of documents of each topic, with the thickness of the line of interconnection between topics directly proportional to the importance or weight of each thematic nexus. Solid lines indicate that the linked topics or themes share the same name, i.e., both topics were tagged with the same keyword, or the label of one of the topics is part of another topic. Dashed lines signify that the topics share elements that do not fit the cluster label. Finally, the overlay graph shows the level of stability between two consecutive periods (Gamboa-Rosales et al., 2020). The number inside the circle represents the total number of keywords in the period. The horizontal arrow shows the number of shared words. The number in parentheses refers to the similarity index between the periods. The outgoing arrow at the top represents the keywords belonging to the first period that are not included in the second period. In contrast, the incoming arrow reflects the number of newly introduced keywords which only exist in the second period (Cobo et al., 2011). 4. Results The 6920 selected documents were imported from WoS and the corresponding filters were applied in SciMAT to avoid duplications and other incorrect records. The resulting final database was 6272 documents. To contextualize the results of the bibliometric study on the field of research on urban passenger transport, we begin by showing a descriptive analysis of the publications, focused on performance indicators during the study period. This century has seen many milestones bearing an important influence on the evolution of UPT. However, our study considers only three of these by which to delineate the analysis to ensure a sufficient number of publications in each period. The year 2010 is identified as the first milestone. Beginning in 2010, a progressive increase in the number of publications on the subject of UPT can be clearly observed, coinciding with the publications of the White Paper "Roadmap to a single European transport area: towards a competitive and sustainable transport policy” (European Commission, 2011) and “The World Bank Annual Report 2010: Year in Review” (World Bank, 2010). The second milestone is the year 2015, as it coincides with the publication of the 2030 Agenda and the Paris Agreement (United Nations, 2015). These agreements represent a commitment by most of the world’s countries to address the environmental, social, and economic challenges caused by climate change. Finally, the third milestone selected is the year 2019, as the end of that year saw the outbreak of the Covid-19 pandemic, bringing with it a major impact on the development of urban mobility. Consequently, the following sub-periods were selected to analyze the evolution of the field over time: 2001–2010, 2011–2015, 2016–2019, and 2020 −2021. Fig. 2 shows the evolution of the number of documents per year. This illustrates an increase in scientific interest during the period analyzed, from 40 documents published in 2001 to 1213 in 2021. In addition, more than half of the publications are concentrated in the last five years, and the most relevant variation is seen in the last year of the study (2020–2021). As will be seen later, this can be attributed factors such as the increase in publications on Covid-19, the growing attention generated by transport in the fight against environmental degradation, and the rapid technological evolution of means of transport and their management. Table 1 lists the number of papers and total citations for the most productive authors in this field. David A. Hensher and Corinne Mulley, both from the University of Sydney and each with more than 50 publications in WoS, demonstrate the highest performance by publication volume. Despite having fewer papers (32 publications), Billie GilesCorti, as co-author, has the paper with the highest number of citations, which dates from 2016. Table 2 shows the 10 documents in this set of publications with the highest number of citations, including the reference of authors, the journal, and year of publication. The results in Table 2 show the diversity of journals that include articles related to the research field. Transport Policy, Preventive Medicine, and Transportation Research Part b-Methodological are the only ones with more than one publication in the top 10 most cited. The most cited article in this research field is "Making cycling irresistible: Lessons from the Netherlands, Denmark and Germany" by John Pucher and Ralph Buehler, published in 2008 in Transport Reviews with 880 citations (Pucher and Buehler, 2008). The analysis of productivity by journal is shown in Table 3. The results in Table 3 indicate that, of a total of 827 journals, the 10 journals with the highest number of papers account for 40 % of the total number of papers analyzed. The journal Sustainability stands out because, although not the oldest journal, it contains the largest number of documents in the research area, with 569 documents (9.07 % of the total number of papers analyzed). Table 4 shows the most common keywords and the number of documents that include them: The analysis highlights the words "travel," "accessibility," "air pollution," "behavior," "health," and "travel behavior," all of which are referenced in more than 500 documents. 4.1. Creation and analysis of the scientific map To analyze the evolution of research in UPT, the sample has been divided into four periods coinciding with certain milestones that modified the way we understand transportation. Fig. 3 shows the number of publications per period. The analysis by period is as follows: 4.2. First period (2001–2010) As illustrated in Fig. 4, the most analyzed transport topics in this period refer to travel, health, and transport policy. The research is D. Verano-Tacoronte et al. European Research on Management and Business Economics 30 (2024) 100239 5 focused on analyzing the behavior of users of different types of transport and on sustainable development measures related to both urban structure and transport policy. As seen in Fig. 4, travel and health appear as driving themes in the scientific field. Work relating to travel focuses on analyzing passenger behavior with respect to different types of transport (public transportation, private car, etc.). It also emphasizes more sustainable travel patterns such as cycling or walking, with the aim of establishing measures to alleviate car use and the accompanying congestion and pollution. When we talk about health, transport relates to modes of mobility that are considered good for health, e.g., walking or cycling, analyzing which measures of space, facilities, etc. and behavioral patterns can influence their optimal use. Transport policy appears as an emerging issue. The reviews show that the sustainable development of mobility in cities, reduced use of private vehicles, and promotion of public transport use directly relate to urban structure and transport planning policies. Therefore, proper management of these policies will have a direct effect on urban transport emissions, congestion, accessibility, etc. Table 5 illustrates the performance measures for this period. Travel has the largest number of documents and the highest h-index, but health, with the fewest documents, has the highest number of citations, indicating the importance of this topic in the analysis of transport. Although the number of citations for transport policy is considered low (468), most of these correspond to the last years of analysis. 4.3. Second period (2011–2015) Fig. 5 shows the seven clusters identified in the second period: physical activity, air pollution, quality, land use, demand, congestion, and social exclusion. Of these, physical activity, quality, and land use are considered driving themes. In particular, the physical activity cluster is closely related to one of the driving themes of the previous period, health. This demonstrates continuity when dealing with issues related to how choice of means of transport and physical activity performance influence the health of individuals. Quality and land use emerge as new driving themes. Growing interest in measuring the quality of public transport is shown, with a primary focus on the study of user satisfaction. Land use refers to issues such as the importance of location for public transport stations or how choice of transport mode affects the existing urban design. In this period, the only basic or cross-cutting theme is demand. This addresses aspects such as the qualitative attributes of public transport that attract different users, estimation of demand for public transport, or modeling of citizens’ behavior and identification of preferences when choosing mode of transport. Fig. 2. Evolution of publications on UPT. Source: Own elaboration Table 1 Authors’ production in research on UPT. Author Documents Citations Citations per document Most cited publication Citations of most cited publication Hensher, David A. 61 2310 38 (Li et al., 2010) 214 Mulley, Corinne 57 1403 25 (Daniels & Mulley, 2013) 162 Cats, Oded 49 1159 24 (Abenoza et al., 2017) 120 Currie, Graham 44 1639 37 (Currie, 2010) 224 Giles-Corti, Billie 32 1885 59 (Giles-Corti et al., 2016) 462 Axhausen, Kay W. 26 808 31 (Meyer et al., 2017) 145 Friman, Margareta 24 1244 52 (Redman et al., 2013) 351 Ceder, Avishai 24 613 26 (Liu & Ceder, 2015) 95 Tirachini, Alejandro 23 906 39 (Tirachini et al., 2013). 182 Nelson, John D. 23 609 26 (Velaga et al., 2012) 138 Source: Own elaboration. D. Verano-Tacoronte et al. European Research on Management and Business Economics 30 (2024) 100239 6 Table 2 Most cited articles on UPT research. Title Authors Year Journal Quotations Making cycling irresistible: Lessons from the Netherlands, Denmark and Germany. Pucher, J.; Buehler, R. 2008 Transport Reviews 880 Existence of urban-scale macroscopic fundamental diagrams: Some experimental findings. Geroliminis, N.; Daganzo, CF. 2008 Transportation Research Part BMethodological 767 Infrastructure, programs, and policies to increase bicycling: An international review Handy, S.; Pucher, J.; Dill, J. 2010 Preventive Medicine 750 Towards a theory of decoupling: degrees of decoupling in the EU and the case of road traffic in Finland between 1970 and 2001 Tapio, P. 2005 Transport Policy 704 Understanding attitudes towards public transport and private car: A qualitative study. Beir˜ ao, G.; Cabral, J.A.S. 2007 Transport Policy 581 The Role of Customer Engagement Behavior in Value CoCreation: A Service System Perspective Jaakkola, E.; Alexander, M. 2014 Journal of Service Research 575 Physical activity in relation to urban environments in 14 cities worldwide: a cross-sectional study Frank, L.D.; Van Dyck, D.; Cerin, E.; Owen, N.; Sarmiento, O.L.; Davey, R.; Conway, T.L.; Adams, M.A.; Cain, K.L.; Mitas, J.; Reis, R.; Salvo, D.; Schofield, G.; Sallis, J.F.; De Bourdeaudhuij, I.; Schipperijn, J.; Pratt, M.; Smith, G.; Kerr, J.; Lai, P. C.; Troelsen, J. 2016 Lancet 573 The dimensions of global urban expansion: Estimates and projections for all countries, 2000–2050 Angel, S.; Parent, J.; Civco, D.L.; Blei, A.; Potere, D. 2011 Progress in Planning 561 Urban gridlock: Macroscopic modeling and Daganzo, C.F. 2007 Transportation Research Part BMethodological 543 Table 2 (continued) Title Authors Year Journal Quotations mitigation approaches. Perceptions about the local neighborhood and walking and cycling among children. Timperio, A.; Crawford, D.; Telford, A.; Salmon, J. 2004 Preventive Medicine 528 Source: Own elaboration. Table 3 Journals with publications on UPT by number of papers. Journal Doc. % Year vol. 1 Impact 2021 Sustainability 569 9.07 2009 3889 Transportation Research Part A-Policy and Practice 395 6.30 1976 6615 Transport Policy 387 6.17 1993 6173 Journal of Transport Geography 346 5.52 1993 5899 Transportation 171 2.73 1972 4814 Transportation Research Part dTransport and Environment 162 2.58 1996 7041 Transport Reviews 129 2.06 1981 10,185 Transportation Research Record 126 2.01 1996 2019 Research in Transportation Economics 114 1.82 1994 2904 International Journal of Sustainable Transportation 113 1.80 2007 3963 Source: Own elaboration. Table 4 Number of documents by keyword. Keyword Number of Documents Travel 727 Accessibility 620 Air pollution 571 Behavior 550 Health 548 Travel behavior 512 Physical activity 470 Car use 449 Quality 416 Demand 384 Networks 649 Energy efficiency 331 Land use 315 Satisfaction 299 Source: Own elaboration. Fig. 3. Number of publications by period. Source: Own elaboration D. Verano-Tacoronte et al. European Research on Management and Business Economics 30 (2024) 100239 7 The air pollution cluster analyzes the influence of transportation on climate change and studies the climate policies being adopted in different countries. This theme very well developed in this period but in an isolated manner. Finally, in the quadrant of emerging or disappearing clusters, we find social exclusion and congestion. Social exclusion is a theme that primarily deals with studies on the influence of poverty on access to the transport system. Its main objective is to address public policies that allow for equitable and socially sustainable urban transport systems. It also addresses studies on the gender perspective in the use of transport. Congestion focuses on the analysis of how to manage traffic congestion through optimal urban public transport design, investment in infrastructure, or developing an appropriate pricing system. As illustrated in Table 6, the topic with the highest performance in this period is physical activity with 107 documents published, an hindex of 47, and 6200 citations. It is followed closely by land use, which surpasses physical activity in number of documents. At the other extreme, we find social exclusion, which has the lowest number of documents and citations and a lower h-index. 4.4. Third period (2016–2019) Here, the contribution is closely related to the use of technology for the development of sustainable mobility, the use of electric vehicles, the implementation of information systems, and measures linked to the reduction of transport-related emissions. In this period, research on transportation focuses on 12 research themes: physical activity, air pollution, satisfaction, optimization, accessibility, travel behavior, demand, performance, accidents, electric vehicles, information systems, and density (see Fig. 6). One driving theme is physical activity, with a similar analysis to that of the previous periods. Other driving themes include air pollution, which changes from being a specialized theme in the second period to a driving theme in the third, satisfaction, travel behavior, and accessibility. Air pollution grows in importance in this period as a result of the 2030 Agenda (United Nations, 2015) and the signature of the Paris Agreement (United Nations, 2015), with countries joining efforts to combat climate change and adapt to its effects. Work linked to the development of measures and plans to reduce greenhouse gas emissions thus increases, especially in association to the use of private vehicles. Regarding satisfaction, studies relate to the identification and characterization of current and potential users of public transport to determine the most important factors that influence satisfaction and loyalty in public transport use. The analysis of transport as regards accessibility is focused on evaluating accessibility both in terms of equity and the implementation of improvements in mobility, such as the use of autonomous vehicles. Lastly, travel behavior appears as a driving theme, with a similar theme to that analyzed by travel in the first period, focusing on passenger behavior by mode of transport. Performance and demand are basic and cross-cutting themes. In the case of performance, transport studies focus on the use of models to evaluate the performance of the transport system from the viewpoint of both sustainability and innovation. Demand maintains the line of the previous period, where it was already located in this quadrant, but it nears that of emerging or disappearing issues in the third period. The main emerging themes that appear in the cluster review relate to electric vehicles, information systems, and density. The theme of electric vehicles focuses on analyzing the different possibilities that electric vehicles assume in the future of sustainable mobility in cities. In information systems, studies focus on mobility improvements in cities through vehicle automation, schedule optimization measures, connectivity services, and the application of artificial intelligence systems in transportation. Density could be considered a disappearing theme, as the works analyzed are in the early years of the period, with studies referring to the relationship between the built environment and chosen mode of transport. Accidents appears as a marginal theme in this period, with focus on explaining the causes of traffic accidents in cities from the point of view of both driver and pedestrian. Optimization falls between marginal and emerging or disappearing Fig. 4. Main themes 2001–2010. Source: Own elaboration Table 5 Measures of performance of the subjects in the period 2001–2010. Name Document Count H-Index Sum Citations Travel 57 32 5101 Health 21 17 5027 Transportation policy 22 14 468 Source: Own elaboration. D. Verano-Tacoronte et al. European Research on Management and Business Economics 30 (2024) 100239 8 topics. It is focused on proposing scheduling models, allocation, etc. to optimize transportation use. Table 7 shows that physical activity continues to have the highest number of documents and highest number of citations. Air pollution has the highest h-index in this period. The number of documents on travel behavior increases from the first period but not the number of citations (4249). 4.5. Fourth period (2020–2021) The strategic diagram in Fig. 7 demonstrates how transportation research in recent years has focused on ten topics: satisfaction, physical activity, accessibility, air pollution, networks, sustainability, efficiency, Covid-19, autonomous vehicles, and service. Research in this period shows thematic areas present in previous periods, but a new trend is observed with the appearance of topics such as efficiency, sustainability, and Covid-19, which impacted transportation greatly in these years. The driving themes identified in the 2020–2021 period are satisfaction, physical activity, accessibility, and air pollution. All were identified as driving themes in the previous period and maintain relevance over time. Service is clearly positioned as a basic theme in this period, within which disparate issues relating to transportation service and user Fig. 5. Main themes 2011–2015 period. Source: Own elaboration Table 6 Performance measures of subjects in the period 2011–2015. Name Document Count H-Index Sum Citations Physical activity 107 47 6200 Air pollution 77 36 3450 Quality 73 28 2765 Land use 121 42 5405 Demand 60 26 2161 Congestion 21 15 732 Social exclusion 17 13 843 Source: Own elaboration. D. Verano-Tacoronte et al. European Research on Management and Business Economics 30 (2024) 100239 15 Ji, W., Yu, S., Shen, Z., Wang, M., Cheng, G., Yang, T., et al. (2023). Knowledge mapping with CiteSpace, VOSviewer, and SciMAT on intelligent connected vehicles: Road safety issue. 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