Literature Reviews

Inequality is embedded in our transportation systems and land use patterns, which reinforces unequal access to opportunities. Mobility inequality can be racialized, gendered, or based on income. The inequalities between those with and without private vehicles deepened during the COVID-19 pandemic [1], [2], [3]. Universal Basic Mobility (UBM) programs aim to address this and in turn create more equitable transportation systems. Based on qualitative evaluation of eight UBM programs and pilots, UC Davis researchers found that UBM pilot programs have had success in enrolling low-income people of color and increasing transit use [4].

Additional research related to equity impacts of mobility wallet pilot program outcomes is ongoing. For example, researchers at UCLA and UC Davis are evaluating the South LA mobility wallet pilot, where 1,000 people in South Los Angeles are receiving $150 per month for a year for use on transit needs [5]. Researchers at UC Davis are also evaluating pilot UBM programs in Oakland and Bakersfield, with a focus on economic, social, and environmental impacts [6]. However, there is little completed research on how effective university mobility programs are in addressing inequality in transportation access. Additional research is needed on the equity impacts of UBM programs, as well as how the programs compare to alternatives like free or reduced fare transit programs.

Mobility-as-a-service (MaaS) applications may have mixed impacts on measures of social equity. Research on the impact of digital apps to facilitate ride-hail shows they lowered transportation inequities for seniors in Japan [1], but maintained existing regional rural-urban disparities in Finland [2]. Unbanked users and those without smartphones may also be left out of use, as well as non-native English speakers, which may exacerbate barriers to mobility faced by those groups [3]. Market dominance by private MaaS companies may also lead to monopolization and price discrimination, which may impact those most reliant on public transportation [3]. Public transportation is crucial for low-income groups, who, paradoxically, find it harder to access than people in wealthier neighborhoods. While MaaS presents an opportunity to enhance accessibility and equity, it's essential for policy makers to address and eliminate barriers that maintain the status quo of exclusion for these communities [4].

Heavy-duty automated vehicles (AVs) could potentially reduce emissions and improve social equity by reducing disparities of residents’ exposure to vehicle emissions and associated health risks. The environmental impacts from heavy-duty vehicles diesel exhaust are particularly severe for residents living close to roadways with heavy truck traffic, such as freeways and major arterial routes in goods movement corridors [1]. Research consistently shows that communities of color and low-income groups are disproportionately situated in areas affected by freight traffic [2], [3], [4]. Patterson and Harley [1] shows that trucks with emission control strategies could result in decreased exposure disparities for pollutants quantified by the intake differentials of two corridors in the San Francisco Bay Area. Operations for designated truck routes, and restrictions on truck parking and engine idling in or near residential neighborhoods can also mitigate the disparities of traffic-related air pollution [5], and automation of heavy-duty vehicles can facilitate the enforcement of these regulations, leading to a more equitable distribution of environmental impacts.
The advent of heavy-duty AVs could also affect employment by disproportionately affecting low-wage jobs in traditional employment sectors. A key concern is the potential displacement of truck drivers [6], [7]. Nikitas et al., [8] concluded that AVs could generate labor market disruption and new layers of employment-related social exclusion based on an online survey of 773 responses from an international audience. Fleming [9] indicated that the technological unemployment on truck drivers will have less economic impact due to the current shortage of truck drivers and aging workforce. Nevertheless, it is crucial for policymakers and urban planners to develop robust retraining programs to prevent these workers from being replaced by higher-wage tech employees.
Overall, heavy-duty AVs have multiple benefits such as reduced driver costs for freight transported by trucks [10], saved fuel consumption and emissions due to platooning and smoother driving [11], [12], [13], and increased safety [14]. However, the study on the equity impacts of heavy-duty vehicles is sparse. Current areas for future research include: 1) exploring the environmental impacts of heavy-duty AV operations, 2) examining the effects of heavy-duty AVs on job markets and identifying effective retraining programs for displaced workers, and 3) analyzing the disparities in potential benefits and risks that heavy-duty AVs pose to different socioeconomic groups.

The social equity impacts of micromobility programs are somewhat mixed. In demographic analyses of bikeshare and scooter share riders in developed countries, studies often find that riders are, based on their income, education, youth or able-bodied status, relatively privileged [1], [2]. Though low-income travelers may be less likely to adopt bikeshare, those who do may use them more intensively and for more trip purposes than more affluent users [3], [4]. Shared micromobility programs designed with docked stations tend to be particularly unequally distributed geographically relative to dockless systems [5]. In light of these demographic and geographic imbalances, it is not uncommon for agencies to impose equity requirements in shared micromobility programs [6]. Social equity research in micromobility focuses on two main components 1) how to incentivize low-income and underrepresented groups to use the services (with a focus on policy measures or direct subsidies linked to spatial equity) and 2) how to include diverse voices in the planning process. Policy analysis is largely linked to geospatial distribution of access to bikeshare, scooter-share, and carshare [7], [8], [9].

Shared micromobility offers an alternative to private driving and thus displaces driving trips that make roads more dangerous and pollute air for everyone. And, it has the added benefit of providing job access and improved health outcomes [10], [11].

Ride-hail, also known as Transportation Network Companies (TNC), may alleviate the high cost of car ownership and reduce mobility gaps across socioeconomic divides by providing people with car trips on an as-needed basis. While the socioeconomic characteristics of ride-hail users vary by region, studies often find that users earn higher incomes than the average resident [1]. However, a small portion of all ride-hail users in California suggests frequent users, those who ride more than three times per week, are more likely to not own a car and earn low-income than those who ride less or non-users [2]. Trip data suggest that most ride-hail users request service only for special occasions which averages three trips per month or less instead of relying on ride-hail for regular travel.

In addition to supporting mobility needs among car-free or car-light households, ride-hail may also address issues of racial bias among taxi drivers. Brown [3] found that Black users were more likely to have a taxi trip canceled or a longer wait than white users; ride-hail exhibited no such ethnic/racial gap in service quality. However, important gaps in access to ride-hail services remain. The benefits of ride-hail can only be seen in jurisdictions that allow them and in markets that support them. For instance, users in rural areas with low population densities and destinations spread far apart account for a small minority of riders [4].

By shifting mobility costs to a per-trip basis, carshare offers benefits for users in two categories: those with a car seeking to drive less (by offering access to a private vehicle without the need for ownership), and those without a car seeking to drive more (by reducing the upfront costs of private automobility). Carshare users tend to be car-less yet relatively affluent [1], which can be explained in part by where carshare stations are placed. Studies find that carshare stations are more likely to be located in higher-income neighborhoods with higher-than-average rates of employment and levels of education [2], [3]. Early carshare adopters tended to be white [4]. However, as the market has matured, recent evidence suggests that after controlling for income, Black and Asian travelers are more likely to use carshare than white travelers [5]. Carshare programs with public subsidies that enable reduced rates for eligible low-income residents are a promising policy solution; they can help people who could most benefit from additional automobility, while expanding carshare stations for all users [6].

On-demand microtransit programs address four aspects of equity: geographic, temporal, economic and social equity. First, microtransit expands transit service by providing flexible routes in lower-density suburban and rural areas where fixed-route services are inefficient or cost-ineffective. Second, microtransit fills gaps in transit operating hours, such as late nights or weekends. Third is economic equity. Microtransit programs are often specifically designed to facilitate commutes and provide a lower-cost alternative to private driving to get to work [2]. Lastly, microtransit placed in disadvantaged neighborhoods can improve mobility access for people who can least afford cars, or people who face mobility barriers, such as elders, low-income individuals, and people with disabilities [3]. Findings are mixed as to whether microtransit programs offer a first-last mile solution to enhance transit ridership, or replace transit trips. Ridership outcomes depend on the specific demands and existing transportation alternatives [1].

A review of the literature yielded no social equity concerns that were independent of workforce-related issues. Those issues are covered under the heading “Education and Workforce.”

Automated vehicle technologies hold significant promise for benefiting vulnerable populations and bridging urban-rural disparities. Demographically, numerous studies highlight the potential of automated vehicles to improve mobility for people with disabilities, elderly individuals, and low-income populations by offering accessible and affordable transportation options [1], [2], [3], [4], [5].
Automated vehicles offer a game-changing solution for individuals with disabilities, including those with vision impairments [6], [7], [8], cognitive impairments [9], [10], [11], or limited mobility [12], [13], [14]. Equipped with advanced sensors and navigation systems, these vehicles could provide safe and reliable transportation for people with disabilities. They could incorporate user-friendly interfaces and assistive technologies, such as wheelchair ramps and voice-activated controls, to ensure accessibility and ease of use [15], [16], [17]. By removing physical barriers and offering personalized assistance, automated vehicles empower individuals with disabilities to travel independently and participate more fully in their communities.
Geographically, the deployment of automated vehicles has the potential to address “transportation deserts” in small urban, rural, or remote areas, providing residents with access to essential services and opportunities that were previously out of reach [18], [19], [20]. For rural areas, where transportation infrastructure may be lacking and population densities are lower, automated vehicles, like other shared ride services, could provide on-demand mobility options and connect residents to employment opportunities, healthcare services, and education centers [21]. Similarly, in small urban areas, where public transportation may be less extensive compared to larger cities, automated vehicles could serve as a flexible and efficient transportation solution, improving mobility and access to resources for residents.
However, the literature also emphasizes the need for careful planning and implementation to ensure that these technologies do not exacerbate existing inequalities. Concerns such as the digital divide [22], [23], [24], affordability [1], [25], [26], [27], and infrastructure limitations [28], [29], [30], [31] in rural and small urban areas must be addressed to ensure that the benefits of automation are equitably distributed across demographic and geographic lines. In addition, the literature emphasizes the importance of community engagement and inclusive planning processes to ensure that the deployment of automated vehicle technologies is responsive to the needs and priorities of diverse communities [18], [32], [33], [34].

Because vehicle-to-everything (V2X), connected vehicle (CV), and connected autonomous vehicle (CAV) technologies have not been widely applied, there is little empirical evidence available about their social equity impacts. However, researchers have used scenario analysis to understand potential impacts. For example, a study from the Urban Mobility & Equity Center at Morgan State University investigated the mobility and equity impacts of connected vehicles as they relate to congestion through a simulated urban network, finding that “the gradual deployment of CVs can significantly improve mobility and equity while saving energy and reducing emissions” [1].
CAVs have the potential to foster an equitable future for disadvantaged communities by improving accessibility, or to create a transportation network that is accessible only to the privileged [2]. Past research [3] has suggested that if CAV policies with regards to social equity are not regulated, disadvantaged populations will face the burdens of lower accessibility and climate impacts. People with lower income, mobility challenges, and historically disadvantaged groups were identified by Cohen and Shirazi as the groups with significant potential benefits from social equity policies of CAVs [4]. Households with low income spend disproportionate amounts of income on transportation expenses [5], which can be reduced by social equity related policies of CAVs including the use of sharing policies for cost distribution over several passengers and/or having policies for the use of non-car modes for sharing such as buses and walking [6]. Shaheen et al. emphasized the importance of expanding active modes of transportation and transit to avoid the replacement of these services by CAVs [7]. Paddeu et al utilized survey participants for acceptability of CV and AVs. They observed in-vehicle security, safety, and affordability as critical factors for acceptability of these technologies [8].

People with age related disabilities would be greatest beneficiaries of CAVs. Claypool et al. proposed that designing CAVs with accommodation for disabilities could serve as a key factor for reducing the accessibility gap between people with and without disabilities [9]. People living in rural areas face challenges of limited walking and biking infrastructure, and transit inaccessibility. Furthermore, people without vehicle ownership or seniors and children have no mobility whatsoever. CAVs have the potential to improve accessibility in such rural areas and make travel more comfortable for rural residents [10]. Lempert et al. performed a scenario analysis to study the equity and accessibility benefits of connected vehicle technology in the United States by 2035, exploring three different scenarios: Mobility for All, Mobility in Transition, and Fragmented Mobility [11]. The Mobility for All scenario represented a future where CV, automated vehicle (AV), and electric vehicle (EV) technology transformed transportation to the benefit of the entire population by 2035, while in the Fragmented Mobility scenario benefits were assumed to accrue only at higher income levels. Mobility in Transition represented a scenario where technology was less advanced and widespread, but there was political commitment to reach underserved populations. The study found that connected vehicles have potential for significant social benefits, apart from the Fragmented Mobility scenario which would result in degradation of health, equity, and accessibility for most of the population [11].This was attributed to the fact that most benefits of CV arise from integration with automation and electrification.

Additional research is needed to understand the full range of how vehicle connectivity could influence social equity. This could include research on social equity benefits of using CAVs for shared mobility and their influence on active modes of travel. Furthermore, there is limited literature on social equity benefits of integrating CVs/CAVs with electric vehicles.