Accessibility disparity between transit and automobile: A study of Atlanta and Seattle

Abstract

This paper aims to study the disparity in accessibility between transit and automobiles, and to understand factors including traffic conditions, transit frequencies, and transit infrastructure that affect the accessibility gap and transit competitiveness. Trips between selected activity centers in Atlanta and Seattle were measured from 7 am to 10 pm to be used as two example cities. Google Application Program Interface (API) was used to estimate travel time and other parameters for each trip. In total, 5472 trips in Atlanta and 8832 trips in Seattle were studied. To compare accessibility between the same origins and destinations by different modes, the ratio of travel time is used extensively, including transit access time and parking penalties. The results suggest the gap between transit and auto accessibility is smallest in morning and afternoon peak hours. Transit travel time and route circuitousness is reduced during peak hours while the automobile has significantly longer travel times during that period. Standalone transit parameters in Atlanta are better than those in Seattle, but when compared to local automobile parameters, Seattle’s transit proves more competitive against automobiles. High quality transit services are also distributed more consistently across the system in Seattle than in Atlanta. This paper demonstrates the importance of comparing transit parameters and system performance to other locally available modes and looking at the distribution of service qualities.