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Review

Transformation of the Urban Energy–Mobility Nexus: Implications for Sustainability and Equity

by
Peerawat Payakkamas
1,*,
Joop de Kraker
1,2 and
Marc Dijk
1
1
Maastricht Sustainability Institute, Maastricht University, 6200 MD Maastricht, The Netherlands
2
Department of Environmental Sciences, Open Universiteit, 6419 AT Heerlen, The Netherlands
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(2), 1328; https://doi.org/10.3390/su15021328
Submission received: 21 November 2022 / Revised: 20 December 2022 / Accepted: 5 January 2023 / Published: 10 January 2023
(This article belongs to the Special Issue A Diversified Approach to Mitigate Crises in Urbanized Areas)
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Abstract

:
In the coming decades, decarbonization of society in response to climate change will result in transformation of urban systems, especially in the energy and mobility sectors. This transformation will likely lead to stronger links between both sectors, which may have both desired and undesirable consequences. However, current policies are predominantly sectoral and tend to assume only a positive impact of the transformation of the energy–mobility nexus on urban sustainability. We conducted a systematic literature review, which covered 78 articles, to identify the interactions between the transformations of urban energy and mobility systems, their impacts on various aspects of sustainability and equity, and the relevant policies that target the nexus. The results show that the positive impacts of the transformation of the urban energy–mobility nexus are outnumbered by negative impacts on various aspects of sustainability and equity. A major equity issue concerns a possible reinforcement of socio-spatial inequalities in access to renewable self-production of electricity, electric vehicles, their integration, and the associated benefits. In conclusion, the issue of socio-spatial inequalities should be a priority for further research and policy development, given the currently limited understanding of these equity risks and the growing emphasis on the need for a just transition.

1. Introduction

Cities are not only the main sources of economic growth and innovation but also play a critical role in mitigating climate change [1]. Urban areas significantly contribute to the global greenhouse gas emissions. These emissions are expected to increase due to the growth of urban populations and the expansion of built-up land and urban infrastructure [1] (The rapid diffusion of greenhouse gases is related to the climatic conditions of a given territory and thereby the availability of qualified workforce and the presence of energy sources to be used for, e.g., heating [2]). Rapid urban growth can create mutually reinforcing lock-ins into high-carbon energy and transportation pathways, which are not easily reversed and thus make the 1.5-°C stabilization scenario unlikely [1,3]. Reinventing energy and mobility, which are generally regarded as being among the main pillars of economic and social development and as the main contributors to greenhouse gas emissions, is required for realizing the needed decarbonization target by 2050 and curbing climate change [4,5,6,7]. A shift in the power generation mix from fossil-fuel power plants towards renewable energy sources is commonly acknowledged as the most obvious way to achieve decarbonization [5,8,9,10]. As the energy supply system is becoming more renewable-based, the transportation sector is also slowly shifting from conventional fossil-fuel vehicles towards low-emission alternatives that are based on electric power-trains, batteries, or hydrogen-based fuel cell technology [9,11,12,13,14,15]. Thus, decarbonization of both energy and transportation has become a priority for many cities and governments worldwide [16,17,18,19,20]. Beyond these aligned sustainability goals, more and strong interactions between the two sectors can be expected through developments such as increased electricity demand and bidirectional electricity flows [18], integrated and smart energy systems [9,21] (An example of renewable-energy-integrated smart grid can be found in Capizzi et al. [22]), substantial upgrading of power grids, and construction of new energy and charging infrastructure [5,10]. These interactions could have positive sustainability impacts.
Therefore, the energy–mobility sector couplings are increasingly recognized for their potential to create synergies for both systems [18]. However, in terms of policy, many cities and governments continue to rely on sectoral, i.e., either energy- or mobility-specific, measures. Energy-specific measures aim to increase the share of renewable energy resources especially in power generation [8,19], to replace conventional power plants with decentralized and renewable-based energy systems [23], and to improve the efficiency of the whole energy supply chain [24,25,26]. Mobility-specific measures involve stimulating the use and/or purchase of electric vehicles [16] and the development of electric vehicle recharging infrastructure [27]. These sectoral policies may shift tensions to other sectors or create new ones [28,29] and may have unintended negative consequences for sustainability or equity objectives [30].
The transformation of energy and mobility systems has also drawn attention to issues of equity such as unequal distribution of benefits of sustainable options or unequal access to which across different social strata [24], districts, and neighborhoods [29]. More specifically, whereas certain measures or developments may benefit the already well-off, for the lower-income strata, they may result in energy and transport poverty and carbon gentrification [31,32,33], exclusion from neighborhoods with high livability as well as from low-carbon transition opportunities [31], and even penalties for their limited access to these opportunities [31,33,34,35].
Current understanding of the transformation of the urban energy–mobility nexus and its implications for sustainability and equity issues are still limited and un-systematized. In some recent scientific publications such as Raven et al. [36] and Sovacool and Griffiths [37], prominent forms of innovation trajectories in both sectors such as solar photovoltaic (PV), alternative fuel vehicles, and automated mobility are identified as important elements for realizing a low-carbon future. However, attention on how these trajectories result in more interactions between the two sectors and affect sustainability and equity in urban contexts is largely lacking. Due to the long-established links between the energy and transportation sectors in terms of energy supply and demand, their interactions are often treated as given rather than as a call for further exploration [38].
Against this background, we conducted a literature review to explore the linkages and potential interactions between the transforming urban energy and mobility systems. A well-established analytical framework was used to systematize the obtained findings. The main aims were to arrive at a systematic overview of possible sustainability and equity impacts of the transforming urban energy–mobility nexus and to identify areas and approaches for further research on these impacts. The guiding questions for the literature search and review in relation to the organization of our article are presented in Table 1.

2. Methods

We employed a systematic literature search to identify existing research on urban energy and mobility transformations, the interactions between these transformations, and the implications of these interactions for sustainability and equity. To select the most suitable key words for the literature search, six key articles, which explicitly discuss the interconnected transformations from various viewpoints (Table 2), were identified.
We used the quantitative data analysis software ATLAS.ti to extract a list of words that frequently appear in the full text of the six key articles. Short functional words that frequently appear but do not convey useful meanings, as well as single-character words, numbers, hyphens (-), underscores (_), and punctuation marks, were removed before counting. The filtered word list was then exported to Excel. With the help of the Power Query Editor feature in Excel, we removed words that did not occur in all of the six articles. The words that were most relevant to our topic and appeared in all the key articles are shown in Figure 1. An asterisk (*) was added to the end of certain words accounted for any possible variations. Boolean operators (i.e., AND and OR) were used to join the key words shown in Figure 1 together to form the search term:
energy AND (power OR electric*) AND (vehicle* OR transport OR mobility) AND (transition* OR transformation) AND (city OR urban) AND sustainab*.
The steps our literature search followed are depicted in Figure 2 (Adapted from Liberati et al. [41], Liu and Dijk [42], and Page et al. [43]). We used the online academic databases Web of Science and Scopus, which support complex Boolean phrases. With the previously mentioned search term, the search in the full text (i.e., not limited to title, abstract, and keywords) of articles that were written in English and available until 22 March 2022 yielded 294 records from Web of Science and 32,104 records from Scopus. The number of records from Scopus was not manageable, and the search in Scopus was narrowed down by adding
AND innovat* AND environment* AND carbon AND policy AND low* AND industr* AND intern* AND market* AND nation*
to the search term. The remaining search result was scoped down by limiting it to relevant subject areas (namely Energy, Environmental Science, Social Sciences, Engineering, Mathematics, and Physics and Astronomy). Throughout these filtering steps, we constantly checked the search result to make sure neither of the six key articles (Table 2) were excluded. In the end, we were able to bring the number of records from Scopus down to 1968.
Sustainability 15 01328 g002 550
Figure 2. Step-wise literature search process.
Figure 2. Step-wise literature search process.
Sustainability 15 01328 g002
Using bibliometrix (An open-source R-tool developed by Aria and Cuccurullo [44]), the 2262 records from both databases were merged, and 36 duplicates were identified and removed. Out of the remaining 2226 records, 149 records that either did not have a digital object identifier (DOI) or contained errors were excluded. The remaining 2077 records were then assessed for eligibility through title-and-abstract reading. The guiding questions presented in Table 1 served as eligibility assessment criteria. On the grounds of relevance to the aims of our study and value for further full-text reading, 1933 articles that could not answer at least one of these guiding questions were deemed irrelevant and removed. The remaining 144 articles were re-assessed for eligibility through full-text reading based on the same set of assessment criteria, which filtered out 78 irrelevant articles. We were left with 66 articles to be included in our literature review. The distribution of these articles per publication year is shown in Figure 3. Outside of this systematic literature search, we also found 12 additional articles that did not return from the search in either Web of Science or Scopus but provided relevant guidelines and insights for our literature review. Any mentions of or references to these 12 articles are put in between the parentheses to create distinction.
In order to map out systematically what the literature reported concerning the linkages and potential interactions between urban energy and mobility transformations, their implications, and associated policies, we used a simplified version of the systems diagram framework (See Sage [45], Sterman [46], and van der Lei et al. [47]). The construction of such a diagram is a means to provide structure to the conceptualization of a complex problem situation. The diagram distinguishes the system itself, the steering factors (i.e., ‘policies’), the external factors, and the impacts of interest or criteria (see Figure 4). Recent analyses consider urbanization and global decarbonization targets the main driver of change in the energy and mobility sectors [25]. Based on these factors, we identified important transformative developments in the urban energy and mobility systems and associated policies, as well as the area in which these systems overlap, i.e., the urban energy–mobility nexus, from the literature. Furthermore, we identified the positive and negative impacts of the transformation of the nexus on sustainability and equity, as well as the policies that target the urban energy and mobility sectors and how they address the impacts (or not). Section 3 presents our findings from the literature review according to the components of the systems diagram (see Figure 4) and the guiding questions listed in Table 1.

3. Results

3.1. External Pressures and Drivers of Change

Growing urban populations and increasing land use for buildings and infrastructure worldwide are putting pressure on the state of the urban energy and mobility systems in the form of growing demands for energy, mobility, and space. At the same time, in the Kyoto Protocol (1997) and, more firmly, the Paris Agreement (2015), nations have agreed to reduce greenhouse gas emissions [48,49,50]. The combination of these pressures exacerbates the challenges for the urban energy and mobility systems [1,3,9]. For example, transport electrification in the increasingly urbanizing and mobile world can burden the power sector with increased and expanded electricity demand [51]. Prioritization of electric driving will result in additional claims on urban land-use [52] to make room for charging facilities [31] and installation of supporting energy infrastructure [52]. A final relevant societal trend that drives or enables changes is digitalization. As in many spheres of life, digitalization is opening new opportunities for smart devices both at the industrial and consumer sides and also in energy and mobility (as described in Section 3.3).

3.2. Current Sectoral Policies

The global climate agreement (noted above) with overarching decarbonization goals has triggered sectoral decarbonization policies. In the energy sector, policies that incentivize sustainable alternatives, e.g., self-consumption schemes for rooftop solar PV [32], as well as policies that constrain fossil-fuel-based options, e.g., phasing out fossil-fuel-based power generation facilities [23], were introduced. In the mobility sector alike, incentives for, e.g., privileges, benefits, and subsidies for electric cars and public (fast) charging [31,32,35], as well as stricter emission standards and low/zero-emission zones [16] and tolls or bans on old and/or ‘dirty’ vehicles [32,35], were widely implemented.

3.3. A Transforming Nexus of Urban Energy and Mobility Systems

Largely unintentionally, the sectoral decarbonization policies have spurred interference between the formerly separated fields of urban energy systems and transportation [4]. A shift towards renewable energy technologies is taking place due to the rapid growth in solar PV and wind energy, especially in power generation [10]. Meanwhile, there is a shift in vehicle–fuel technologies and power-trains towards low-carbon ones that are powered with renewable energy [1]. To a large extent, this shift involves the electrification of transportation with battery electric vehicles and, to a lesser extent, the application of hydrogen-based fuel cells [9,11,12,13,14]. To serve the increasingly diversified electricity demand and accommodate the weather-dependent renewable energy production, whilst maintaining systems stability, the need for (long-term) storage of electrical energy will increase strongly in the form of electric batteries [8,9,10,53,54] and/or hydrogen (through electrolysis). This development, combined with the electrification of transportation, results in a further increase in the overlap of urban mobility and energy systems, as various forms of vehicle–grid integration, which allow vehicles to serve as mobile and distributed forms of storage for renewable-based electrical energy, have emerged [30]. In this way, said vehicles form a backup for renewable-based power generation [39,52] and facilitate the integration of such volatile energy sources [4,26,33,39]. These bidirectional concepts are expected to find significant applications in future smart grids and smart mobility systems and are made possible or more effective by developments in digital technology [6,55,56]. The electrification of transportation, as well as other sectors such as heating of buildings (replacing gas, coal, wood, etc.), will result in a much higher demand for electricity and the need for a large-scale expansion of new renewable energy systems, substantial upgrading of power grids, and construction of vehicle charging infrastructure [5,10].
In addition to decarbonization, the decentralization of energy systems is another trend in the increasing interconnection of energy and mobility systems [40]. The simplicity of solar PV systems enables installation (often on rooftops) and power generation at or next to the site where energy is needed and gives rise to local grid systems and local energy management. Examples are shared solar systems for medium- and high-density housing projects and community-based energy storage [1]. Compared to conventional power plants, the production of solar and wind energy is much more decentralized and requires more land [23,57]. This use of land can result in so-called ‘energy sprawl’ [58]. Although solar parks and wind turbines are mostly built outside cities, these renewable energy facilities also sprawl into peri-urban areas. Electric vehicles allow for highly decentralized ways of recharging at night at home or during daytime at the workplace. Electric vehicles’ battery capacity also enables the potential use of said vehicles for decentralized storage, reserve, and backup for intermittent, locally generated renewable electricity [39,52,55], as mentioned earlier, which falls under the umbrella of vehicle–grid integration [26,30,33,39]. Such strategy includes technologies that range from smart electric vehicle charging (when prices are lowest) to various concepts of bidirectional electricity flow, or any combinations thereof (see Aggarwal and Singh [59]).
Rapid developments in digitalization have enabled transformational changes in both energy and transportation systems that are often referred to as smart grids and smart mobility [6,55,56]. Digital metering and control systems enable better monitoring, coordination, and management of multiple types of energy supply and demand in increasingly decentralized smart grids [6,21,25,32,55,56,60]. Digitalization has also opened options for households and communities to virtually consume solar electricity that is fed into the grid elsewhere, to co-own a solar power plant among a range of neighbors, or to engage in peer-to-peer energy transactions [32]. In the mobility sector, ICTs support drivers by identifying the fastest route, the next available parking space, and the closest charging station for electric vehicles [61]. Moreover, distributed sensors provide real-time information on, e.g., public transport timetables, traffic conditions, and localization, reservation and payment of shared vehicles. These sorts of information support the integration of multiple modes of transportation and the shift from private vehicles towards service-based, on-demand, and sharing business models through online platforms, e.g., integrated ticketing in Mobility-as-a-Service (MaaS) concepts [4,32,62]. Both in the energy and mobility sectors, ICTs are expected to provide smart, simple, and flexible interfaces between users and network operators and could foster the development of peer-to-peer and transparent transactions [25], as well as advanced communication and data exchanges between the increasing number of actors and possible actions [56]. In this way, digitalization supports the increasingly multi-party nature of transportation through, e.g., coordinated charging, on-demand mobility services, and verification and communication platforms for cross-border traveling.
Deliberate sectoral decarbonization policies have, largely unintentionally, triggered an expanding urban energy–mobility nexus that is characterized by decentralization and enabled by digitalization. These changes in the urban energy and mobility systems are summarized in Table 3. Section 3.4 will focus on the impacts of these changes at the nexus of urban energy and mobility. No attention will be paid to, e.g., the (many) impacts of the shift to renewable energy sources as such or impacts that are felt outside cities.

3.4. Impacts of the Transformation of the Urban Energy–Mobility Nexus

3.4.1. Environmental and Livability Impacts

If primarily supplied by renewable electricity, the electrification of transportation will substantially reduce greenhouse gas emissions and air pollution in cities [12,20,27,33,53]. However, a widespread adoption of electric vehicles will increase the demand for electricity and, if the electricity is still produced from fossil fuels, lead to increased greenhouse gas emissions in the power generation sector [63]. In that case, switching from fossil fuels for vehicles to electricity will only shift pollution from local, city-bounded vehicle tailpipes to power plants that tend to be located outside the city [33]. Thus, electric mobility can support the decarbonization only when electricity is produced, transmitted, and distributed through low-carbon means [12,64].
Even when electricity is only obtained from renewable sources, mass electric vehicle uptake will likely perpetuate the current car-centric forms of mobility and associated problems such as traffic congestion, competition with other modes of transportation, and disadvantaging non-car users [31,32,61]. The perceived environmental benefits of electric driving may even produce a rebound effect of escalated driving [31,32,61]. Private electric vehicles still require the same amount of space as their internal combustion engine counterparts do [34] and will likely continue to promote a car-centric city, in which public space is prioritized for private car users, rather than geared towards public and non-motorized transportation [32,61]. Additionally, battery and bidirectional capacities of electric vehicles, which are crucial for balancing and stabilizing the increasingly renewable-integrated power grid, endorse the paradigm of private vehicle ownership and might compel even more driving [31,33]. In this way, mass electric vehicle uptake may end up preserving/accommodating auto-mobility and competing for both urban space and public funding that could be allocated to other, more sustainable forms of mobility such as active and public transportation (e.g., construction of more bicycle and bus lanes).
Further, the increasing demand for renewable electricity and the resulting ‘sprawl’ of decentralized renewable energy facilities, e.g., wind turbines in peri-urban areas especially, will result in larger numbers of nearby residents who experience negative effects such as noise, vibration, and shadowing of properties [23]. Urban renewable energy projects, capacity expansion and upgrading of the power grid, and implementation of a dense public charging infrastructure for electric vehicles will intensify the competition for urban space and will be conflicting, with the goal of creating more green and livable cities [31].
Without grid reinforcements, higher levels of electric vehicle adoption will pose stress on the electric distribution network and will give rise to many challenges concerning grid stability [8,65]. The expanded amount of driven electric mileage and consumed electricity will place extra power demands and multiple intra-day demand peaks, which may exceed transformer ratings of the distribution network or cause line congestion and voltage deviations, in case of contemporary connection between the grid and several customers [5,51]. These problems can further intensify when electric vehicle adoption is geographically dense (i.e., at the neighborhood scale) and when the charging demand is temporally concentrated due to collectively adopted driving and charging patterns among users [51]. Management and coordination of electric vehicle charging will be necessary to mitigate the peak power problem, in which the intra-day demand profile of electric vehicle charging largely overlaps with that of household electricity use [66]. Moreover, with limited available grid capacity, larger-scale urban renewable energy projects will leave private house owners with less room to inject their excess self-produced solar electricity into the grid and benefit from a self-consumption scheme [32].
Whereas the electrification of transportation and other sectors might negatively impact the resilience of urban communities due to the reliance on a single source of energy, which may be disrupted by, e.g., natural disasters, widespread adoption of vehicle-to-grid systems might have a counteractive effect. If electric vehicles were charged prior to the disaster, they could provide a (temporary) source of electricity for households [33].

3.4.2. Economic and Equity Impacts

The decentralization of renewable energy production in form of private rooftop PV panels brings the opportunity for electric vehicle owners to recharge at home with cheap, self-produced electricity [1]. Decentralized, local electricity storage in the form of vehicle–grid integration brings additional benefits for electric vehicle owners as well. Such benefits include reduced vulnerability to interruptions in power supply and financial benefits from using the electric vehicle as a power source during peak-demand hours and while recharging during the nighttime [26,33,39]. However, in the last decade, access to electric driving has been unequal across socio-spatial groups. Adoption is highest among the wealthier (i.e., high-income, highly educated, and highly mobile) sections of society [31]. In turn, owning and using electric vehicles brings multiple benefits such as the home option for charging, reduced parking fees, access to zero-emission zones, and exemption from congestion tolls, which potentially also add to the rebound effect of escalated driving among the already well-off [24,31]. Adoption of electric driving also tends to be higher among those who live and/or work in urban cores with shorter routine trip distances and more choices of transportation [1,31,61]. These benefits of electric driving and charging are currently not accessible to low-income individuals who live in the outer districts and in rented, multi-apartment buildings with little to no private space for parking and charging an electric car at home during the nighttime [23,31]. To realize these benefits, considerable retrofitting would be necessary but would raise housing costs to renters who would, when said retrofitting is not possible, then be compelled to continue driving their old and dirty cars [31]. Moreover, in the case of the anticipated large-scale vehicle-to-grid implementation [67], electric vehicle charging may be prioritized and thereby compete with other temporally inflexible energy needs (for cooking, heating, lighting, laundry, etc.) and negatively affect low-income households [33,68], which most likely do not own an electric vehicle or vehicle–grid integration technology [32,33].

3.4.3. Overview of Impacts

The developments at the urban energy–mobility nexus have promising positive impacts on urban sustainability but also have negative (potential) effects on various aspects of sustainability and equity. The identified impacts from our review are categorized as positive (+) and negative (−) and presented in Table 4.

3.5. The Need for ‘Nexus Policies’

New policies to anticipate the potential positive and negative impacts of the transformation of the urban energy–mobility nexus should be measures, incentives, and strategic plans that can mitigate the negative impacts of the transformation and stimulate the positive impacts. Most of the identified current policies encompass strategies that target developments and sustainability gains within a single sector (see Section 3.2). As noted, these policies have spurred increasing shares of renewable energy in power generation [8] and implementing pro-electric-vehicle measures [16,63]. In addition to being sectoral, these measures typically concern technological improvements such as efficiency improvement of the energy supply chain [24,25,26], implementation of decentralized energy systems [23], and deployment and integration of sustainable energy technologies [18].
The scientific literature raised the following points of awareness. First, strong policy support for mass electric vehicle uptake will not solve a range of problems that are caused by the dominant role of cars in the urban mobility system [17,69]. Second, sustainable mobility also requires policies that aim at, e.g., a reduction of driving, a modal shift to public and active transportation, and a deeper discussion of a post-car society [31]. There appears to be less awareness of the negative impacts on equity of current transportation policies that aim at a shift to electric vehicles. Low-income groups that do not have access to expensive electric vehicles and live in the outer parts of the city will be ‘penalized’ for their—on average—longer commute by road tolls and will have limited access to city centers because of the bans [32,35].
In contrast to the widespread attention for policies that are aimed at sectoral sustainability gains (Studies of socio-technical transitions have addressed co-evolutionary transformation of both energy and mobility systems but typically focused on either one or the other [4], e.g., Verbong and Loorbach [70] on energy and Geels et al. [71] on mobility), policies that target the equity aspects of the transformation have been explicitly addressed by only a few authors and hardly translated into actionable policies. El Hachem and De Giovanni [35] demonstrated how the distributive justice aspect of the transition to alternative fuel vehicles, in terms of fair access to transportation, could be translated into an indicator and addressed in trade-offs with environmental objectives. Schippl and Truffer [72] explored how innovation trajectories in mobility could work out differently in divergent spatial settings and recommended policymakers and planners to develop spatially sensitive strategies. Pucci [61] conducted a socio-spatial analysis of electric vehicle diffusion and proposed diversified and site-based policy measures for a transition towards low-carbon mobility that is both effective (i.e., stimulating electric vehicle diffusion and reducing emissions) and fair (i.e., ensuring basic accessibility to all).
Attention of policymakers specifically for the urban energy–mobility nexus is limited to (the advantages of) vehicle–grid integration [26,30,33,39]. Only in a few cases, the literature acknowledged the need to take a more integrative, inter-sectoral approach through embracing aspects of either inter-regional energy collaboration [73], smart energy community and sharing economy [1,32], integrated urban and infrastructure planning [1], or circular economy [12]. Cross-sectoral cooperation is hampered, however, by institutionally fragmented policy (sub)domains and actors, who are not equipped to organize such cooperation due to their tendency to focus on incremental amendments within their own jurisdiction and area of responsibility [29]. This challenge is further complicated by the disparities between jurisdictions (i.e., electricity market, institutions, and regulations) that are involved in grid integration of renewable energy, electric vehicles, etc. [26].

4. Discussion and Conclusions

4.1. Key Findings

From this literature review, a clear picture of the ongoing and anticipated transformations of the urban energy–mobility nexus (Table 3) has emerged. The key development is the emergence of electric driving, which in turn has led to further interactions between urban energy and mobility systems. Said interactions range from the various forms of vehicle–grid integration to the need for an expansion of local renewable production of electricity, power grid, and charging infrastructure. Global decarbonization targets and subsequent sectoral decarbonization policies are the main drivers of these developments, whereas digitalization has been a major enabler with smart grid and smart mobility technologies. Current policies are mainly sectoral and are actively supporting the ongoing developments, while focusing on the sustainability gains. The impacts of this transformation of the nexus on various aspects of sustainability are widely reported in the literature (Table 4). The most attention is given to the positive impacts of electric mobility, in particular the reduction of urban emissions of greenhouse gases and the improvement of urban air quality. However, as Table 4 shows, these sustainability benefits are traded off by a wide range of interconnected negative impacts and risks that include concerns about the equity of the transformation. These concerns are grounded in the current and anticipated unequal distribution of the benefits and burdens associated with the emergence of electric driving across social strata.
When taken together, an underlying pattern and risk of increased socio-spatial inequality, which has not received explicit and systematic attention in the literature thus far, emerges. The underlying pattern consists of both social and spatial factors that determine the distribution of benefits and burdens that follow from the transformation of the urban energy–mobility nexus, as well as the reinforcing interactions between these factors and their effects. Income level is an important social factor that determines the access to electric mobility, given the high prices of electric vehicles. The same applies to access to self-production of electric power among households with PV panels. In both cases, a range of benefits such as subsidies and exemptions, which are usually intended as incentives, follows from having access to self-production with PV panels. This access is also determined by spatial factors, most importantly the availability of a well-exposed rooftop space. Another spatial factor is the availability of private parking space at one’s own premises. This factor determines access to home charging of electric vehicles. Therefore, access to important benefits of a further integration of urban energy and mobility systems, namely home charging of electric vehicles with cheap self-produced electricity and the anticipated benefits of vehicle–grid integration, depends on both social and spatial factors. As a low income often coincides with living in neighborhoods with apartment blocks without private rooftop space and parking space (and vice versa for high incomes), access to all these benefits is socio-spatially highly unequal. This inequality is even further enhanced by a range of ‘penalties’ for those who do not own an electric vehicle or PV panels (Table 4). Such penalties can lead to possible future effects such as less reliable power supply and declining public transportation services. The result is an accumulation of positive impacts for certain socio-spatial groups in urban society and an accumulation of negative impacts for others.

4.2. Implications for Research and Policy

Currently dominant policies that target the transformation of urban energy and mobility systems are largely motivated by the goal of climate neutrality. This singular focus has resulted in developments at the urban energy–mobility nexus that run counter to other urban sustainability objectives such as more urban green space or reduced car use. The literature shows awareness of these issues and has repeatedly called for more integrated and coherent policies with respect to energy and mobility transformations [40]. Development of such policies requires research efforts to better focus on the interactions and couplings between these two sectors, to identify the synergies, and to comprehensively evaluate the possible sustainability trade-offs [19,29,69,73]. More recently, there is a growing attention to the equity aspects of the energy transition, the emphasis on the ‘justness’ of the transition, and the concern about the likelihood of persisting and even intensifying inequality patterns unless targeted measures are put into place [29,32,61]. In order to contribute to the discussion of where policy interventions should be directed to effectively foster urban transformations, research should not only have a more integrative and broader scope [74,75,76] but also connect environmental sustainability objectives with ones that seek to reduce inequality, poverty, and exclusion [35,75].
According to this review, the transformation of the urban energy–mobility nexus creates a serious risk of perpetuating and enlarging socio-spatial inequalities and may even result in energy and transport poverty among a large and often vulnerable part of urban populations. However, in the literature, there has been limited attention on how social and spatial factors interact in the allocation of benefits for one group and burdens for another [61]. This lack of understanding and the current absence of policy measures to address and mitigate these effects lead to the following conclusion: The issue of socio-spatial inequalities should be a priority for further research and policy development. To develop policies that promote the sustainable transformation of the urban energy–mobility nexus in a socio-spatially inclusive way, a better understanding of the underlying mechanisms and the socio-spatial groups at risk, as well as a joint knowledge production process that include researchers, urban policymakers, and, preferably, residents, is required. For a better understanding of the mechanisms by which the transformation of the urban energy–mobility nexus, as well as current policies result in socio-spatial inequalities, the empirical database is too limited, as most developments are still in an early stage. Therefore, the analysis of empirical data should best be complemented with expert consultations. Based on an improved understanding, socio-spatial indicators of risk or vulnerability may be identified and applied in Geographic-Information-System (GIS)-based analyses to determine the relative risk levels for the different parts of the population and the city [32,55]. Combining understanding of the nexus dynamics and GIS, an ex ante approach could be followed [40] by exploring and evaluating various policy scenarios jointly by researchers, policymakers, and residents, who bring in different value perspectives, evaluation criteria, and types of knowledge. As single policy instruments rarely achieve a wide range of sustainability and equity goals, the focus should rather be on policy mixes or packages [3,11,40,77] (For example, Kern et al. [78] demonstrated the use of policy-mix thinking as an analytical perspective in the context of supporting sustainable energy transitions).

4.3. Conclusions

This literature review set out to explore the linkages and potential interactions between the transforming urban energy and mobility systems. The main aims were to arrive at a systematic overview of possible sustainability and equity impacts of the transforming urban energy–mobility nexus and to identify areas and approaches for further research on these impacts. In response to climate change, decarbonization targets and policies are the major drivers of the transformation of the urban energy and mobility sectors, but decentralization and digitalization are also important trends. Major developments are decentralized, renewable-based production of electricity and electric driving. These developments have shown to bring the two sectors closer together, yet the scientific literature is fragmented in this respect and lacks a clear overview. Towards fulfilling this knowledge gap, the key findings from our literature review are as follows. Whereas current policies for the transformation of the urban energy–mobility nexus tend to focus on or assume the positive impacts, which mainly include reduced urban greenhouse gas emissions and improved urban air quality, these benefits are outnumbered by negative impacts on various aspects of sustainability and equity. A major equity issue concerns inequality in access to renewable self-production of electricity, electric vehicles, their integration, and the associated benefits. As this access depends both on social and spatial factors, the transformation of the urban energy–mobility nexus may reinforce socio-spatial inequality patterns. Given the growing emphasis on the need for a ‘just transition that leaves no one behind’ and the currently limited understanding of the equity risks that are associated with the transformation of the urban energy–mobility nexus, our recommendation for future research and policy development is to give priority to the issue of socio-spatial inequalities.

Author Contributions

Conceptualization, P.P. and J.d.K.; methodology, P.P. and J.d.K.; software, P.P.; formal analysis, P.P., J.d.K. and M.D.; investigation, P.P., J.d.K. and M.D.; resources, P.P., J.d.K. and M.D.; data curation, P.P., J.d.K. and M.D.; writing—original draft preparation, P.P.; writing—review and editing, J.d.K. and M.D.; visualization, P.P., J.d.K. and M.D.; supervision, J.d.K. and M.D.; project administration, P.P., J.d.K. and M.D.; funding acquisition, P.P. and J.d.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Key words used in the literature search and their frequency of occurrence across the six key articles. Sustainability 15 01328 i001: Canzler et al. [4] Sustainability 15 01328 i002: Oldenbroek et al. [9] Sustainability 15 01328 i003: Boucher and Mérida [24] Sustainability 15 01328 i004: Di Silvestre et al. [25] Sustainability 15 01328 i005: Sovacool et al. [39] Sustainability 15 01328 i006: Dijk and Kivimaa [40].
Figure 1. Key words used in the literature search and their frequency of occurrence across the six key articles. Sustainability 15 01328 i001: Canzler et al. [4] Sustainability 15 01328 i002: Oldenbroek et al. [9] Sustainability 15 01328 i003: Boucher and Mérida [24] Sustainability 15 01328 i004: Di Silvestre et al. [25] Sustainability 15 01328 i005: Sovacool et al. [39] Sustainability 15 01328 i006: Dijk and Kivimaa [40].
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Sustainability 15 01328 g003 550
Figure 3. Number of included articles per publication year.
Figure 3. Number of included articles per publication year.
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Figure 4. Simplified systems diagram applied to the transformation of the urban energy–mobility nexus.
Figure 4. Simplified systems diagram applied to the transformation of the urban energy–mobility nexus.
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Table
Table 1. Guiding questions for the literature search and review.
Table 1. Guiding questions for the literature search and review.
SectionTitleGuiding Questions
Section 1Introduction
  • How are the interactions between urban energy and mobility transformations interesting?
  • How could said interactions impact sustainability and equity?
Section 3Results
  • What is the transformation of the urban energy and mobility systems about?
  • How do or can urban policy-making and planning affect these transformations?
  • What are the key linkages and possible interactions (i.e., nexus) between the two transforming sectors?
  • What are potential impacts of these linkages and interactions on sustainability and equity specifically?
Section 4Discussion and Conclusion
  • On which aspects of the urban energy–mobility nexus do the reviewed articles mostly focus?
  • What are the current knowledge gaps, and on what aspects is more research needed?
Table
Table 2. The six key articles and their main features.
Table 2. The six key articles and their main features.
Key ArticleMain Feature
Canzler et al. [4]points out the emergence of a new field at the intersection of renewable energy systems, transportation, and information and communication technology (ICT) in the analysis of the local context of an urban innovation campus in Berlin, Germany.
Oldenbroek et al. [9]offers a system design, energy balance, and cost analysis of a fully renewable-integrated transportation and energy system for smart European cities, based on existing technologies (solar and wind electricity, fuel cell electric vehicles, and hydrogen).
Di Silvestre et al. [25]analyzes the impacts of today’s main drivers for change (i.e., decarbonization, decentralization, and digitalization) on the key power infrastructures (including the electrification of mobility) in the United States, Europe, and China.
Sovacool et al. [39]introduces various aspects and visions of vehicle–grid integration, based on a comprehensive review, and outlines a research agenda on un(der)studied topics (e.g., the need for institutional capacity and cross-sectoral policy coordination).
Dijk and Kivimaa [40]discusses the policy challenges to low-carbon transformation based on the emerging interest in policy mixes and policy innovations that are linked to the increasingly interconnected energy and mobility fields.
Boucher and Mérida [24]presents regression and geographic analyses of the socio-spatial distribution of access to electric vehicles in Washington State and calls for policy that can direct society towards greater equality.
Table
Table 3. Trends and developments in urban energy and mobility systems. Developments that concern specifically the energy–mobility nexus are indicated in bold. See text for details.
Table 3. Trends and developments in urban energy and mobility systems. Developments that concern specifically the energy–mobility nexus are indicated in bold. See text for details.
Decarbonization
  • growth of solar and wind energy in power generation [10];
  • low-carbon vehicle–fuel technologies: electric batteries and fuel cells [1];
  • electrification of transportation and heating [30];
  • implementation of (long-term) electricity storage: hydrogen and batteries [8,10,15,54];
  • construction/expansion of renewable energy facilities, power grids, and charging infrastructure [5,10].
Decentralization
  • decentralization of (renewable) energy systems [23,25,40];
  • expansion of electric vehicle charging infrastructure to households and workplaces [5,10,27,31];
  • vehicle–grid integration: electric vehicles as storage [26,30,33,39].
Digitalization
  • virtual energy communities and peer-to-peer energy transactions [25,32];
  • smart grids [21,55];
  • smart mobility [4,61].
Table
Table 4. Impacts of the transformation of the urban energy–mobility nexus. See text for details.
Table 4. Impacts of the transformation of the urban energy–mobility nexus. See text for details.
Impacts
Positive (+)Negative (−)
  • reduced tailpipe emissions of greenhouse gases [20,33];
  • improved urban air quality [20,33,53];
  • localized, cheap, self-produced electricity for home charging [1];
  • reduced vulnerability to interruptions in power supply with vehicle–grid integration [26,33,39];
  • shifting power demands to the most favorable periods for the user/grid [26,33,39];
  • energy saving due to digital optimization of driving paths [61,62].
  • increased emissions in the power generation sector due to increased electricity demand, in case of a fossil-fuel-dominated generation mix [63];
  • perpetuated problems of car-based urban mobility [31,32,34,61] and discouraged uptake of more sustainable (i.e., active and public) transportation [31];
  • unequal distribution of benefits from and access to electric mobility [24,31,61];
  • penalizing (suburban) low-income residents with increased taxes/tolls and fuel costs while depriving them of parking privileges, access to urban centers, etc. [32,35];
  • increased number of people who are affected by negative impacts of decentralized electricity production due to increased demand [23,32];
  • increased competition for urban space between land use for the urban energy–mobility nexus with alternatives including urban greening [31,52,58];
  • unequal distribution of benefits from self-production and self-consumption of electricity and vehicle–grid technology [32];
  • exerted stresses on electricity network resulting in reduced reliability and scarcity dilemmas [8,65];
  • competition of vehicle charging with temporally inflexible energy needs of low-income households [31,32,33];
  • reduced urban and community resilience due to reliance on electricity as the single energy source [33];
  • increased vulnerability to privacy and (cyber-)security threats [29,56].
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Payakkamas, P.; de Kraker, J.; Dijk, M. Transformation of the Urban Energy–Mobility Nexus: Implications for Sustainability and Equity. Sustainability 2023, 15, 1328. https://doi.org/10.3390/su15021328

AMA Style

Payakkamas P, de Kraker J, Dijk M. Transformation of the Urban Energy–Mobility Nexus: Implications for Sustainability and Equity. Sustainability. 2023; 15(2):1328. https://doi.org/10.3390/su15021328

Chicago/Turabian Style

Payakkamas, Peerawat, Joop de Kraker, and Marc Dijk. 2023. "Transformation of the Urban Energy–Mobility Nexus: Implications for Sustainability and Equity" Sustainability 15, no. 2: 1328. https://doi.org/10.3390/su15021328

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