Using GIS for Measuring Transit Stop Accessibility Considering Actual Pedestrian Road Network

Bus stops attain their importance to the transit service from being the main points of contact between the passenger and the bus. Considering spatial attributes, both the location and the spacing of bus stops significantly affect transit service performance and passenger satisfaction, as they influence travel time in addition to their role in ensuring reasonable accessibility. Knowing that every transit trip begins and ends with pedestrian travel, access to a bus stop is considered a critical factor for assessing the accessibility of the stop location. In this research, transit stop access coverage is estimated based on the actual pedestrian road network surrounding the stop. Accordingly, new indices are developed to assess a bus stop location on a more spatial basis. These indices measure the accessibility of a bus stop through the surrounding road network in addition to the ratio of actual access coverage to the ideal access coverage of a stop. Introduction Being the first points of contact between the passenger and the transit service, access to public transport stops is an important factor affecting overall transit trip travel time. Physical access to a transit stop is interpreted in terms of the proximity of the passenger’s origin or destination to the nearest transit stop (TCRP 1996), Journal of Public Transportation, Vol. 13, No. 4, 2010 24 which is generally achieved by walking, riding a bicycle or driving a car for a short distance (Murray and Wu 2003). In planning for the provision of bus-based transit service, accessing a bus stop is considered to be achieved mainly by walking. Based on an assumed average walking speed of about 1.3 m/s, 5 minutes of walking is considered reasonable in urban areas, which is about 400meters in terms of walking distance (Levinson 1992). Most transit firms consider 400meters an acceptable access/egress standard (Ammons 2001). In Columbus, Ohio, it is stipulated that passengers do not exceed walking distances of 400m to transit stops in urban areas (Central Ohio Transit Authority 1999). In general, access to transit stops affects passenger accessibility and represents the opportunity to use the public transport service (Holtzclaw 1994). Estimating Bus Stop Access Coverage Although pedestrian access to a bus stop is achieved through the pedestrian road network surrounding each stop, previous research has not focused on the interaction between bus stop locations and their surrounding pedestrian road networks. Stop access coverage has been estimated using a circular buffer analysis with a radius of the access threshold around the transit stop in order to identify its coverage area. Knowing this area in addition to the population density, the total number of individuals in a region having suitable access can be determined. Another approach for estimating access is by comparing the distance from the centroid of a spatial block to its nearest bus stop. If this distance is within the threshold distance, then coverage is achieved (Murray et al. 1998). Both approaches provide simple estimates for access coverage; however, they are unrealistic and have potential for error by measuring the access distance in terms of a rectilinear distance and ignoring the actual geography of the pedestrian road network surrounding the stops. Estimating Actual Bus Stop Access Coverage Bus stop access coverage is a critical measure for evaluating the stop location by estimating the covered area and population lying within a suitable access distance from the bus stop (Foda and Osman 2008). However, much previous research treated stop coverage as a simple circular buffer with a radius of the access threshold around each stop, which causes an overestimation of the stop access coverage. The reason for such an overestimation is the implied assumption that passengers can reach the bus stop from any location within the circular buffer (ideal case),