2.1 The Concept of Accessibility
Hansen (1959) proposed the concept of accessibility as "the potential of interaction," while Weibull (1980) defined it as "a property of the configuration of opportunities for spatial interaction." A precise definition has been proposed by Geurs and van Wee (2004). According to them, it is the extent to which land use and transport systems enable individuals to reach activities or destinations utilizing transport modes. It is the ease of reaching destinations or activities called opportunity (Litman, 2002; El-Geneidy and Levinson, 2006). According to Ross (2000), "The ease of reaching some destination may include real or perceived costs in terms of time or money, distance traveled, level of comfort, availability, and reliability of public transport or any combination of these."
Accessibility is not only considered mobility (physical movement) but also considers other factors that affect the access to opportunities, location of the opportunities, patterns of land use, the quality and affordability of transport options, and people's ability to use those transport options (Levinson, 2020). It has other meanings in different fields, such as in geography and urban economics; it refers to the relative ease of reaching a particular location or area. In pedestrian planning and facility design, accessible design (also called universal design) refers to facilities designed to accommodate people with disabilities (e.g., a pathway designed to accommodate people in wheelchairs may be called accessible). In the social planning field, it refers to people's ability to use services and opportunities. So, it can be said that accessibility is the ultimate goal of most transport, which generally refers to physical access to goods, services, and destinations (Ahsan, 2013).
2.2 The Concept of Job Accessibility
Job accessibility is the "ease of reaching workplaces" or the "potential of job opportunities for interaction" (Hansen, 1959). It comprises three sub-systems: transport, worker's residence, and jobs, further categorized into spatial and non-spatial distribution. The spatial distribution ensures a connection between the worker's residence and job location. Besides, the non-spatial distribution contributes to the variation of mobility provision through transport sub-systems (service schedules, traffic management, and planning policies) (Cheng and Bertolini, 2013).
2.3 Accessibility Measurement
Accessibility comprises four distinct components: land use, transportation, time, and the individual (Geurs and van Wee, 2004). Therefore, accessibility measurement should be sensitive to changes in either or both components. It is commonly divided into place-based and person-based accessibility measures. Place-based accessibility measures at a specific location in space often include only land use and transportation elements. Besides, person-based measures focus on individuals incorporating time budgets and socioeconomic data (Geurs and van Wee, 2004). This study is considered a place-based accessibility measure.
Place-based measures are divided into three categories: Cumulative opportunity measure, gravity-based measure, and Utility-based measure (Deboosere and El-Geneidy, 2008). The cumulative opportunity measure quantifies the number of reachable destinations from a designated spatial place within a predetermined time frame, employing a specific transportation mode. (Ingram, 1971; Morris et al., 1979). It quantifies the number of opportunities using a particular mode of transport considering a specific time (often 30 or 45 minutes). Numerous extant research examines the concept of job prospects, whereas many other chances encompass various domains such as healthcare, clinics, educational institutions, retail establishments, and more (Geurs and van Wee, 2004). The metric under consideration considers the principle of equal opportunity while disregarding values beyond a certain threshold and does not include passengers' subjective impression of time (Ben-Akiva and Lerman, 1979). It can identify the most significant accessibility areas and ascertain equity disparities across different groups (Tomer, Kneebone, Puentes, & Berube, 2011; Ross & Svajlenka, 2012; Guthrie, Fan, & Das, 2016).
Gravity-based measures also consider the distance between the destination or opportunities. If the opportunity is a larger distance from the origin, it will be considered as less accessible. This measure does not consider a certain time threshold. The statement adheres to Tobler's first law of geography, which posits that the opportunities in proximity to the point of origin hold greater value (Hansen, 1959; Owen and Levinson, 2014). The gravity measure dampens opportunities as time or distance from the origin increases. It is used to measure job accessibility by a specific mode of transit from a particular place (Levinson, 1998; Di Paolo, Matas, and Raymond, 2014). It can also combine with a multinomial logit model to decide mode selection and accessibility individually (Cervero, Sandoval & Landis, 2002). However, it has some criticism, including generating meaningless values and overestimating the accessibility score.
Finally, the Utility-based accessibility measure assigns a given utility to each destination and calculates the log sum of all destinations within a probable option set. Thus, utility-based accessibility can be estimated using the multinomial logit model as the denominator (Handy and Niemeier, 1997). It emphasizes the benefits that individuals derive access to spatially dispersed activities.
2.4 Consideration of Equity in Transport Literature
According to Litman (2017), equity (justice or fairness) is referred to as the appropriate and fair distribution of impacts (benefits and costs) among all. Equity has two main approaches: horizontal equity and vertical equity (Litman, 2002). Horizontal equity is known as the equal distribution of benefits among all social classes. Vertical equity in public transportation requires the distribution of benefits according to the needs of each social class for those services (Murray and Davis 2001).
According to Kahn et al. (2008), low-income families tend to congregate in areas close to central business districts because of the convenience of public transportation. According to research conducted by Ong and Miller (2005), the "transport mismatch theory" posits that there is a disconnect between the supply and demand for citizens to use various forms of transport to get to and from work. The social significance of a product was used as a measure of fairness in its distribution by Martins et al. (2012). People's interpretations of the social significance of public transport systems might vary widely. For captive users (those who rely on a single motorized mode to complete their intra-urban trips due to a lack of car ownership or access or age-related travel conditions), public transportation is a necessity, while for choice users (those who rely on at least two motorized modes to complete their intra-urban trips and can choose a transit or paratransit mode), it is merely an option.
Bertolaccini (2013) conducted her research in eight metropolitan cities in the USA to check whether the distribution of transit services is equitable across these cities. The researchers also check how the equity level changes with the spatial dimension change. In that case, the level of equity is measured for both the Metropolitan Statistical Area (MSA) and the Transit Service Area (TSA) using the general transit feed specification (GTFS) database. The supply index was derived using the frequency intensity method, and the demand index was calculated considering the total population of MSA and TSA. Finally, the disparity between the supply and demand index was measured, and the Gini-coefficient value was generated.
2.5 Relationship between Accessibility and Equity
In order to perform better urban transportation research, it is crucial first to understand the relevance of transportation planning and how it affects accessibility. The subsequent phase may involve determining the level of accessibility for various places and socioeconomic categories (Lucas et al., 2016). Traditional transportation and land-use strategies frequently overlook the influence of distributional implications on the travel capacity of urban populations with various social identities, economic levels, and skill and aptitude levels. This is a critical matter. One of the main aims of transportation policy is to provide equitable mobility for all city and metropolitan residents, especially the poor and socially disadvantaged. Therefore, accessibility equity analysis is essential. However, to inform land-use regulations and policies about how they could affect different populations' access to and utilization of social and economic opportunities, it is critical to understand the distribution of accessibility from both a transportation and an effect of land-use on travel behavior standpoint (van Wee and Handy, 2016). The connection between equity and the ease of using public facilities has been the subject of much debate (Grengs, 2015). Public facilities and services provided by nonprofits have a redistributive impact because they lessen the impact of the wage system on the most vulnerable individuals in society (Harvey, 2010).
Multiple instances highlight the significance of equity in the formulation and assessment of public policy in the global literature on the subject of accessibility and equity (Delbosc and Currie, 2011a; Lucas et al., 2016; van Wee and Handy, 2016; Wu and Hine, 2003). According to Lucas et al. (2016), traditional methods of evaluating policies, including cost-benefit or multi-criteria analysis, run the danger of overestimating the positive impacts on certain groups while ignoring others. A number of studies in the field of transportation have used scale-independent metrics like Lorenz curves and Gini indices to examine accessibility and vertical equity comprehensively (Delbosc and Currie, 2011a; Grengs, 2015; Karlström and Franklin, 2009; Lucas et al., 2016). Such indicators are supposedly easy for policymakers and decision-makers to understand and work with. Delbosc and Currie (2011a) investigated equity in Melbourne's transport system, whereas equity in Stockholm's congestion pricing scheme was investigated by Karlström and Franklin (2009). In addition, Wu and Hine (2003) and Grengs (2015) conducted calculations to determine accessibility for different social groups, with a particular focus on equity, even if Lorenz curves were not present.
2.6 Past Research on Accessibility and Equity
There is a lot of literature on the topic of transportation-related social exclusion. A major claim made by this research is that insufficient or nonexistent mobility options lead to social marginalization (Preston and Rajé, 2007). Lack of access to opportunities is both a cause and a consequence of social exclusion, according to Kain (1968), Kenyon et al. (2002), Manaugh and El-Geneidy (2012), Sanchez et al. (2004), and Wee and Geurs (2011), who emphasized the mobility and accessibility perspectives on the links between transportation disadvantages and social exclusions. Using the UK's Department of Transport's accessibility planning initiatives as a case study, Preston and Rajé (2007) investigated the reliability of accessibility as an indicator of social exclusion. There has been less effort to quantify accessibility for low-income people despite equity being a prominent theme in accessibility studies. Since there are frequently non-spatial hurdles to obtaining high-wage work, these accessibility indicators offer a more accurate picture of the accessibility situation for marginalized groups (Legrain et al., 2016). Legrain et al. (2016) note that most studies that measure accessibility to jobs do not specifically measure access to low-income jobs, meaning that they do not assess more valuable destinations for socially vulnerable populations. However, most studies do find that vulnerable groups experience higher accessibility levels overall (e.g., Foth et al., 2013).
It is surprising that measuring accessibility to vulnerable people has received so little focus, given the abundance of equity-focused accessibility studies. Because there are sometimes non-spatial barriers to attaining high-wage occupations, these measures better represent the state of access for disadvantaged groups (Legrain et al., 2016). Contrarily, most research that looks at job accessibility also reveals that vulnerable persons have a greater level of accessibility (Foth et al., 2013). Research on vulnerable groups of people's job access gets little attention in the USA, especially compared to the cities within a state. This study adds to the existing literature on job accessibility by comparing accessibility measures and examining the resulting equity of the interaction between transportation and land use in four major cities in Ohio. The aim is to offer a more comprehensive perspective on the fairness of public transportation services in Ohio.