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Assessing Transportation Equity Considering Individual Travel Demand and The Feasibility Of Trip Mode Alternatives
Transportation access is an important indicator of the quality of life and if it is inequitable, it will limit the work, leisure, and other essential opportunities for people and worsen the access for the disadvantaged groups. In the U.S., increased auto-dependency and the lack of other feasible alternative transportation modes exacerbate the negative impacts of this inequity, especially for the people without automobiles. The transportation equity in terms of the number of feasible transportation mode alternatives to serve a trip (i.e. mobility option equity) has not been extensively evaluated in the literature. Existing studies mainly analyzed the access to transportation infrastructures (e.g., bus stops, bike lanes, shared bike stations) based on the proximity at the zonal level. However, having access to a certain trip mode based on proximity does not necessarily add to the mobility option equity. First, mismatch may exist between the infrastructure and an individual’s travel demand. For example, if someone lives closely to a bus station but the bus route that can be accessed does not align with this person’s trip destination, they will not be able to use bus as a feasible mode for this trip. Second, existing accessibility-based studies often lack consideration of the trip feasibility (in terms of cost, quality, and safety) of using transportation infrastructures at the route level. For example, if a walking trip route is generated without considering the existence of sidewalks, the individual might have to walk on a unsafe busy road. In this case they will not be able to walk to satisfy their travel demand. Therefore, better transportation equity metrics concerning the feasibility of using transportation infrastructures to serve individuals’ travel demands are needed.
To address this gap, this thesis defined the “travel-demand-relevant access” (mobility-need-relevant access) metric to evaluate transportation access in the context of individual travel demands and route-level infrastructure constraints and developed a framework to use GPS data to quantify the proposed metric for transportation equity analysis. Assessing which transportation modes are feasible alternatives to serve a trip, requires trip-level disaggregated travel demand data and detailed transportation infrastructure information. The recent development of information and communication technologies and open data efforts provide unprecedented opportunities for such trip-level analysis. With these developments it is now possible to evaluate the feasibility of a mode both the cost- and quality-based measures. The cost-based method estimates the monetary and time cost of using each mobility option and compares it with prominent trip mode (car) to examine “forced car use” concerning the travel demand. The quality-based method comprises accessibility and mobility-based performance measures to evaluate the feasibility of a certain trip mode regarding the ease of use and safety with relation to the infrastructure characteristics. The mobility options/alternatives deemed feasible with these two methods were used in the equity analysis, where the travel-demand-relevant access on the spatial and sociodemographic level was evaluated.
The proposed framework was applied to the Indianapolis Metropolitan Planning Area (MPA) as a case study. The key insights of this study can be listed as (1) it is important to consider travel-demand-relevant access to evaluate transportation equity because we found that 40% of the trips that were identified as accessible by public transit are not feasible when travel-demand-relevant access is considered; (2) suburban areas on average have 12% less mobility options available compared with the urban core which forces high car ownership in these areas; amd (3) people with non-college educational attainment, households with more crowded rooms, and larger families are the negatively impacted disadvantaged groups while census block groups with high composition of white middle-class suburban families have the lowest number of options (1.5 on average) available.
The suburban populations with a low number of mobility options (with a vehicle) are not necessarily at a disadvantage in terms of mobility option equity, since suburban areas are by design made to be car dependent. However, the lower number of feasible mobility options in these areas possesses a risk for the future if the consequences are not evaluated carefully. In terms of urban migration, if out-migration from the urban core to suburban areas keeps increasing as the pandemic trend suggests, the forced car ownership in suburban areas could increase and create/worsen transport deserts. This increase in vehicle ownership contradicts equity and environmental goals regarding transportation. If we observe an increase in the suburban to urban core migration trend, it can force disadvantaged groups to move into suburban areas because of gentrification and increasing prices. These disadvantaged groups could suffer from the limited amount of mobility options in suburban areas, since their access to opportunities would decrease.