By 2050, 68% of the world’s population will reside in cities, according to the United Nations [1
]. Urban freight transportation plays a crucial role in the development of big cities and impacts how well people’s quality of life is supported. Additionally, it promotes logistics competitiveness and supports commercial and industrial activity conservation and maintenance. However, adverse transportation side effects impact social, economic, and environmental measures. This problem worsens when it comes to heavy cargo. Their operational characteristics (such as speed and agility) and physical qualities (such as length and size) hurt their neighboring traffic. They are generally diesel-powered, so they have more detrimental environmental effects, such as increased air and noise pollution [2
]. The problem with the big freight vehicles in urban areas is made even worse by traffic congestion. Heavy freight vehicles typically tend to generate more traffic congestion than smaller vehicles. Heavy trucks in the United States consumed nearly 20% of additional fuel in 2020 because of traffic congestion [3
The growth of retailing, initially in conventional brick-and-mortar stores and, more recently, via the internet, has been driven by the rampant consumption of commodities and the increased desire for convenience in shopping. E-commerce allows products to be bought anywhere in the digital world and then delivered to the final user, typically in a city, after travelling across the globe. Since 1993, this sector has experienced tremendous growth and is now generally acknowledged as a standard method for conducting business [4
]. Approximately 300% more money was spent online between 2014 and 2019. Internet sales increased from 8% in 2012 to 20% of all retail sales in 2021, according to data from the United States [5
]. In addition, the COVID-19 pandemic and the sanitary crisis further contributed to the rapid growth of e-commerce. According to a recent McKinsey survey conducted in the US, 30% of respondents said they switched from purchasing in-store to online shopping because of the pandemic [6
The last mile of the products’ shipment is known to be the most challenging of all with respect to several factors, such as cost, efficiency, and emissions [7
]. By 2030, the global demand for last-mile delivery is anticipated to increase by 78%, leading to a 36% increase in the number of delivery vehicles in 100 cities [8
]. It is predicted that by 2030, last-mile deliveries will increase congestion by 21% and emissions by 36% [9
]. This phenomenon has led to tremendous negative environmental impacts, specifically in the urban areas where most of the population is concentrated. City logistics has been striving to discover environmentally friendly solutions that would lessen traffic jams and other negative consequences that freight transportation has on the environment. Several strategies exist to tackle this issue, including the use of freight consolidation facilities [11
], bento box solutions (i.e., pack stations) [12
], last-mile deliveries with electric vehicles [13
], and delivery during off-peak hours [6
Urban consolidation centers (UCCs), also referred to as urban distribution (or delivery) centers (UDC), are responsible for streamlining the infrastructure, business processes, and services that connect the interurban and urban supply chain sectors. Before being sent for last-mile distribution, intercity freight is consolidated and sorted in UDCs. This process eliminates the need for trucks to transport component loads into metropolitan areas. Instead, smaller and more environmentally friendly vehicles with high load-utilization rates would handle the last-mile deliveries. Therefore, using UDCs can improve the effectiveness of the distribution system and ease social and environmental burdens associated with urban freight [16
]. The public and supply chain participants gain from UDCs despite the expenditures connected with their creation and management [17
]. In a study by Navarro et al. [18
], the authors discuss that the costs associated with the UDC operations (in Sao Paulo, Brazil) are justified by the socio-economic, environmental, and financial advantages, such as improved operations, lower greenhouse gas (GHG) emissions, lower hospitalization and premature mortality costs, related to exposure to local pollutants.
A UDC facility location is a crucial aspect that affects its success. The search for the best place for facility building is the focus of UDC’s position, commonly known as the “location dilemma.” It is a decision-making issue with substantial interrelationships between the affected region and socio-economic, business, environmental, safety, and transportation ramifications. There are two ways to consider the locations of the UDCs: (1) close to the urban population, which is economically advantageous but will cost a lot in terms of increased traffic and air pollution; or (2) far from the urban population, which is advantageous in terms of reducing traffic and air pollution but becomes costly in terms of distribution and transportation costs and longer distance travelled. Due to the size and complexity of large cities and urban areas, choosing a UDC location necessitates a thorough analysis of all environmental, demographic, social, and economic factors. These factors include accessibility, security, connectivity to multimodal transport, costs, environmental impact, proximity to customers and suppliers, resource availability, compliance with sustainable freight regulations, and the likelihood of natural disasters. The potential places are identified based on the evaluation of the parameters. Next, key decision-makers and stakeholders take part in rating each of these suggested places. The total scores are computed in most cases, and the UDC location with the highest score is chosen. Sensitivity analyses are helpful in establishing how criteria weights affect the decision-making process. Assessments of a variety of location-allocation strategies permit logistics firms to construct new distribution facilities while considering the sustainable freight specifications supplied by city governments for planning last-mile deliveries [19
The realized and conceptual benefits of UDCs align well with the corporate governance (CG) and corporate social responsibility (CSR) initiatives. The growing popularity of responsible operations and conscious consumerism, as well as the enforced governments’ policies on restricting carbon footprints (such as enforcing a carbon tax and emission trading system), has put significant pressure on companies to be more transparent about how they measure and manage environmental, social, economic, and governance-related risks and opportunities. UDCs’ core premise on promoting sustainable urban freight transport well-positions them as a long-term winning solution that contributes to the complex challenge of fighting climate changes in urban areas and decarbonizing the freight transport market. In this paper, we closely review the literature on UDCs that contribute to various aspects of CG and CSR and follow our discussion by identifying gaps and proposing future research agendas.
The layout of this paper is as follows: we describe our research focus and methodology in Section 2
; Section 3
and Section 4
discuss our findings from our bibliometric and network analysis of the extant literature; then, in Section 5
, we survey the pertinent literature under themed rubrics; and finally, in Section 6
, we conclude and offer several potential research venues.
3. Bibliometric Analysis
We initiated our study of the UDCs by conducting a bibliometric literature analysis. Bibliometric analysis is a scientific approach of software-assisted review that can pinpoint critical features of publications (including authors, affiliations, year of publication, publisher, etc.) relevant to a particular topic or field. This employs statistical and mathematical analysis techniques that enable the collection of trustworthy quality indicators. As a result, data on the number of documents published by an organization or a nation, research teams, or people with the highest scientific production may be found. In recent years, bibliometric analysis has become incredibly popular in business research. Bibliometric tools (e.g., Gephi, Leximancer, and VOS viewer), scholarly databases (e.g., Scopus and Web of Science), as well as the cross-disciplinary pollination of the bibliometric methodology (from information science to business research), contribute to the popularity of this approach [7
]. We use Web of Science (WOS), a trusted publisher-independent citation database. In Table 1
we show keywords selected as “inclusion criteria” within the abstract, topic, and title of the research papers. This search returns 112 items.
In our bibliometric analysis, we include various terminologies used to refer to urban distribution centers. In what follows, we discuss reviewed papers with respect to top-publishing authors, years, countries, affiliations, publication titles, and publishers. We set our baseline to identifying the top 10 in each category; however, we exceed this count on a case-by-case basis, whenever we deem truncation to the top 10 does not fully represent a fair demonstration of the results.
3.1. Publication Years
The study of urban freight consolidation first appeared in the literature in 1978 and 1979. Both studies were pursued in the USA at the University of Texas, Austin, and the University of Tennessee. However, following the initial studies, UDCs did not attract any attention in the literature for two decades. In the noughties, the study of urban consolidation started gaining attention again and four papers were published during this decade. In the early 2010s, this topic started gaining momentum with a hike in the annual publication rate in 2017. Given that 10 out of 11 papers published this year originated in Europe, a possible explanation for this sudden incline could be the European countries’ strong support of the suitability initiatives proposed in the Paris Agreement in 2015 that entered into force in November 2016. In 2020, we observe a sudden decline in publication rates which can be explained due to the COVID-19 pandemic disruptions. Nonetheless, this decline is mostly recovered during the subsequent years 2021 and 2022. In Figure 2
, we illustrate the publication timeline in the study of UDCs.
3.2. Top-Publishing Authors
Next, we aim to identify the top 10 publishing authors. We recognize in total 298 authors publishing in this area and list the top ones in Table 2
. The number of articles to which the top-publishing authors contribute is within the same range, with the top four authors contributing to four and the remaining seven contributing to three publications. Given that the subsequent seven authors each contribute to the same number of articles, we list the top eleven publishing authors. In Table 3
, we also present the institution to which each author is affiliated as well as the country in which the affiliation is located. It is apparent that the authors affiliated with European institutions have made outstanding contributions in this area. Almost half of the top-producing authors (six out of eleven) are affiliated with Europe. This count is, respectively three, one, and one for authors affiliated with Asian, South American, and Australian institutions. Note that we refrain from summing up the record counts associated with countries in one continent to avoid multi-counting some articles that are written by co-authors from different countries.
3.3. Top-Publishing Affiliations
In Table 3
, we recognize the top-publishing affiliations, from a total of 168, along with the country they are located in. We keep the top fifteen in this list since the last nine affiliations have the same count of publications. Consistent with our results on the most contributing authors, we discern 10 European affiliations on the top 15 list, reflecting their significant contribution to this field of knowledge. The count of top contributing affiliations is two in Asia and one in each of the continents North America, South America, Asia, and Australia.
3.4. Top-Publishing Countries
In Table 4
, we study research trends based on the countries the co-authors are associated with to gain insight into the demographics of relevant research activities. We identify 36 countries and list the top 15 in Table 4
. Only the last five entries in this table represent countries located in Asia and Australia, each with a count of four contributions; therefore, we include them in Table 4
for an inclusive representation of record counts across the globe. Interestingly, although the USA does not appear in the list of top-contributing authors and we only spot one American institution in the list of top-contributing affiliations, it transcends all the other countries in the total number of articles generated. This implies that relevant research in UDCs conducted in the USA is decentralized, i.e., it is not central to one (or a few) author(s) or affiliation(s). Italy, with the second-highest count of articles, follows a similar analogy. Nevertheless, there are countries where the majority (or even all) of the total count of publications in the area of UDCs is designated to a few author(s) or affiliation(s). For instance, while the total record count in India is four, the record count of the Indian Institutes of Technology is also four, which suggests that research is strongly centralized to one affiliation in the country. Consistent with our results from previous subsections, we observe significant contributions by the European countries; nearly half of the countries recognized on this list are European (seven out of fifteen).
Reasons that contribute to extensive research conducted in European countries include having: (1) highly developed urban areas and urban freight transport, (2) increased purchase power, (3) internet access triggering augmented e-commerce, (4) road transport limitations proportional to urban area size (road transportation in Europe accounts for on average of almost 76% of all inland freight transport between the years 2010 and 2018), and last but not least, (5) highly incentivizing sustainability initiatives compliance and commitment following the Paris Agreement as explained in Section 3.1
3.5. Publication Titles
We recognize 56 publication titles (journals) and illustrate the top 12 in Table 5
. We include two additional entries (entry 11 and entry 12) as they have the same record count as the tenth journal on the list. We represent the record count and record percentage to, respectively, capture the number of and the percentage of papers published per publication title. Finally, we report the journals’ publishers and their 2021 SCImago Journal Rank (SJR). JSR indicator is a measure of the prestige of scholarly journals that accounts for both the number of citations received by a journal and the reputation of those journals. The average SJR rank of the top 12 publication titles is 1.35.
We recognize 27 publishers and illustrate the top 12 in Table 6
. Similar to publishing titles, we report on two additional entries as they have the same record count as the tenth publisher. We represent the record count and record percentage to, respectively, capture the number of and the share of papers published by each publisher. With a record count of 41 articles, which accounts for more than a third (36.6%) of all published articles, Elsevier surpasses the other publishers. It is noteworthy to mention that Elsevier is ranked four in Table 5
where we identify the publishers associated with the top producing journals, insinuating that this publisher is not reliant on one (or a few) journals, but rather their large count of contributions originates from publication in the multiple numbers of their journals. In Table 5
, it is observed that half of the listed journals (six out of twelve) are published by Elsevier. In fact, Elsevier is the third largest publisher (with respect to the number of journals), following Springer and Taylor and Francis Group [20
]. All three publishers emerge in Table 6
. Other publishers in Table 6
that are included in the world’s top 100 largest publishers as outlined in [20
] are SAGE (in rank 5), IEEE (in rank 18), and MDPI (in rank 15).
4. Cluster Analysis for Authorships and Keywords
To perform co-authorship and keywords analysis, we use VOS viewer, one of the most effective tools that helps draw useful bibliometric network illustrations. It enables the construction and visualization of co-occurrence networks of significant keywords taken from scientific literature using text mining as an exclusive feature.
We first study co-authorship to show cooperation between academics. This tool helps to construct a network among co-authors by checking the authors’ number of publications and where they work together. Association by stronger authors is visualized by the number of co-authored articles. A filter criterion of at least 35 citations has been applied here for the authors. A complete counting method is applied to the network analysis to count the total number of authors’ appearances in all papers. As the next step, we implement re-ordering with normalization and strength association, resulting in three clusters of A, B, and C, as illustrated in Figure 3
Cluster A (red-colored network) in Figure 3
mainly focuses on UDCs. It underlines research by renowned authors who have written multiple articles and co-occurred together various times. All the authors’ names (such as Awasthi, Browne, and Taniguchi) have numerous studies on UDCs around various topics such as sustainability, developing models to measure the impact of UDC, and economic contributions. Cluster B (green-colored network) detects the co-occurrence of authors who reflect more on urban transport, optimizing city logistics, and freight transport. Authors such as Crainic, Taniguchi, and Browne are clustered together. Here, UDC has been discussed as a feasible solution for solving city transport issues. In Cluster C (blue-colored network), the co-occurrence of authors mainly stems from conducting research around critical factors that impact the UDC or urban freight transport. “Cost” and “policy barriers” are examples of significant elements that can contribute to the overall success of UDCs.
In the second phase of our network analysis, we performed a co-occurrence analysis on the keywords of the studied articles. Similar to the authors’ analysis above, we conducted a full counting method of the keywords’ appearances in the articles and then applied a filter criterion of at least 50 citations. Duplicates and ambiguous keywords have been removed for better visibility as in Figure 4
. Strongly associated nodes are positioned closer together, whereas weakly associated nodes are positioned farther apart. We identify four clusters, A, B, C, and D, as illustrated in Figure 4
Cluster A (red-colored network) in Figure 4
is the largest cluster with the close association and co-occurrence of keywords between various models around consolidation centers and various algorithms used to maximize the impact of UDCs in terms of sustainability. Cluster B (green-colored network) is a keyword association around stakeholder analysis and speaks about stakeholders’ behavior and response to UDCs within the contexts of city logistics and partnerships, such as receiver-carrier. Cluster C (blue-colored network) is mostly around optimizing freight, strengthening the incorporation of the handling process into the supply chain, and reducing operating costs. Cluster D (yellow-colored network) provides an overview of where UDCs can be sited considering a variety of socio-environmental, economic, and governance initiatives.
The study of keyword co-occurrences in Figure 4
reveals that the clusters created cover prominent topics in governance and corporate social responsibility. More specifically, Cluster A explains issues in socio-environmental and compliance with sustainability initiatives. The wide range of topics concerning stakeholders in Cluster B overlays governance. Cluster C explains economic benefits. Finally, Cluster D includes articles that present a holistic point of view. With that understanding, we further exclude areas that are not central to this study in the WOS search and focus our attention on the 80 most relevant publications. Section 5
explains our classification of the literature and paper included in each class.
6. Discussion and Direction for Further Research
The rapid growth of urbanization on the one hand, and the increased popularity and accessibility of e-commerce on the other hand (especially during the pandemic), have caused large cities to face complex challenges, such as pollution, congestion, noise, and climate change. This problem has invoked vigorous research around analyzing, describing, and seeking solutions to the issue of green last-mile deliveries within urban cities. UDCs have been proposed in response to this issue with the warrant to restrain large delivery trucks from entering large cities and, instead, allow urban freight to be received and sorted in the proximity of large cities. Last-mile logistics is then outsourced and scheduled to distribute freight to the final urban destinations utilizing sustainable transport vehicles, such as fully loaded small vehicles that are electric or low emission. The UDCs’ added leverage to plan sustainable urban freight transport aligns them with increasingly enforced governments’ and municipalities’ policies to reduce carbon emissions.
Our review of relevant literature initiates by performing a comprehensive bibliometric analysis to gain insight into several descriptive aspects of the existing literature, such as the distribution of most frequently published journals, publishers, authors, affiliations, and countries, as well as the timeline of the conducted research. Our cluster-based network analysis represents the co-occurrence of highly cited keywords and co-authors. Our network analysis results guide us to identify two main streams of studies: (1) papers that discuss ideas around the stakeholders’ governance regarding the system of rules, practices, and processes by which UDCs are directed and controlled, and (2) papers that discuss the socio-environmental and economic impacts that UDCs establish. With that, we use our descriptive analysis results to identify some of the most impactful papers, categorize them through the lenses of corporate governance (CG) and corporate social responsibility (CSR), and conduct an in-depth review to discuss their most significant findings. We also recognize gaps and shortcomings in the literature review, which we explain below.
Governance. Utilizing UDCs should encourage both monetary and non-monetary benefits for all participants when incorporated into a sustainable urban logistics system that reduces the overall costs of distributing goods through cities. When financial benefits cannot be realized in the short term, mechanisms are needed to offer equitable and effective cost-sharing for stakeholders participating in UDC networks. Especially with limited funding, local authorities could find it very challenging to coordinate a range of objectives (across the social, environmental, and economic dimensions) connected to numerous categories of private stakeholders, while considering the everyday commercial operations or logistical planning procedures of private players. For UDCs to become financially viable, it is important to advance responsibility-sharing initiatives that aim to end the initial situation in which such facilities are exclusively dependent on subsidies from local and federal governments.
Aligning resources toward greening city logistics under the United Nations Sustainable Development Goals (UNSDGs) is imperative. Unsustainable urban development poses extensive problems that need to be tackled in synchrony and determination by all the stakeholders: citizens, government, regulators, businesses, policymakers, civil society organizations, city animals and the environment, among others. To that end, interdisciplinary research that develops a framework and actionable research paths are required: particularly, UNSDG #11 (Sustainable Cities and Communities), #9 (Industry, Innovation, and Infrastructure) and #12 (Responsible Consumption and Production) could be simultaneously used as guideposts for developing sustainable solutions to target the alarmingly increasing global city logistics and urbanization problems. A quadruple bottom line approach (see, [84
]), whereby the four pillars of sustainability (economic, social, environmental, and cultural well-being) are considered for city logistics, is becoming imperative.
Another area of investigation that warrants the successful implementation of UDCs is deploying advanced technologies, such as the internet of things and blockchain (e.g., [86
]) along with increased delivery capacities of crowdsourcing (e.g., [89
]) to plan and schedule UDC deliveries. Such methods offer innovative ways to incorporate the measurement and control of sustainability performances in greening city logistics. However, it is imperative to explore whether the additional energy consumption and shared-capacities these emerging intelligent technologies bring justify sustainable last-mile deliveries.
Corporate social responsibility. Based on the literature review, one area that is not fully explored is a full-fledged study of the social impact of using UDCs concerning corporates’ ethical and philanthropic responsibilities. Such studies can be crucial in assessing how UDCs act and how much they contribute to the community. Below, we explain two areas we deem worthwhile social contributions while greening city logistics.
Integrating spatial proximity to low-income communities into the objective of the location-allocation problems. The soaring cost of living and real estate prices within cities usually pulls more low-wage workers (including vulnerable, marginalized, and food-insecure families) out of downtown areas and into suburban areas. With the UDCs located on the outskirts of large cities and close to such communities, these centers can engage in more social activities that help such communities thrive. The impacts can include providing employment opportunities, complementary health insurance and benefits, local charities and food banks support. Such a strategic location-allocation approach provides an equitable opportunity to include individuals from diverse backgrounds as the workforce which ensures that businesses and individuals are conscientious of the influence they have on the world around them and actively engage in protecting the environment, helping those in need, supporting local communities, and cultivating positive influences on society and education.
Securing last-mile delivery opportunities for sustainable and innovative technology trends. Logistical options for shipping and fulfillment have expanded with the rapid growth of e-commerce, cloud, and mobile computing solutions. While this growth has created many opportunities for businesses, it has also raised the standard of consumer expectations. Exploiting new technology in planning last-mile deliveries from the UDCs could stifle future growth. Alternatively, UDCs can plan in advance to strategically construct their facilities in a location that facilitates using such advanced technologies (e.g., green vehicles, drones, autonomous trucks, and e-bikes).