When more destinations cost more: accessibility and equity in a fixed-route-to-microtransit conversion

Transit agencies increasingly replace fixed-route service with zone-based, on-demand microtransit and present the change as a coverage improvement. Yet these conversions replace one generalized-cost structure with another. Riders may gain access to more destinations, but they may also face longer waits and fares that rise with trip length. Conventional threshold measures capture expanded reach but ignore added travel costs, so a conversion can appear to improve accessibility even when trips become more burdensome. A conversion can therefore appear to improve accessibility even when trips become more burdensome. This study examines an implemented conversion in Seminole County, Florida. It calculates accessibility for every residential parcel before and after the change across six destination categories. The analysis uses observed service conditions rather than assumed parameters and tests a continuum of impedance specifications. The conversion expanded geographic reach but imposed an almost constant generalized-cost penalty on every trip. Results depended on the accessibility measure. For grocery access, the same data produced an accessibility ratio of 1.900 under a threshold measure but 0.457 under a gravity-based measure calibrated to the model’s cost ceiling. Every gravity specification tested indicated a loss. Equity effects were modest overall but consequential for destinations where substitution is difficult. Losses were mildly regressive for commuter rail and dialysis access on both equity screens, but after accounting for spatial dependence only the commuter rail dependency gradient cleared the multiple-testing threshold. Applying an older-adult walking speed produced a larger effect than the service conversion on these two screens. Because that effect was concentrated in the least transit-dependent areas, it reversed the direction of the other equity findings. The main contributions of this study are: First, it shows that disagreement between threshold and gravity accessibility measures can be reduced to two measurable parameters. Researchers can therefore calculate the decay value at which the measures reverse their ranking before selecting a decay assumption. Second, the same closed-form result identifies the pickup wait at which a conversion would leave accessibility unchanged. This converts an equity assessment into a service standard that can be calculated from a proposed zone map and fare schedule. However, the findings describe one context; the approach should be adapted to local conditions before it is applied elsewhere.