Measurement And Application Of Spatial-temporal Accessibility By Public Transit Integrating GPS Data

Spatial-temporal accessibility by public transit reflects the public transit system's ability for trading time for space through assessing individuals' spatial-temporal constraints within a public transit network.Measuring spatial-temporal accessibility by public transit can be employed to evaluate the service level of a public transit network and guide trip planning for passengers,and it is meaningful for aiding bus network planning and bus scheduling.Previous studies focused on measuring individuals' spatial-temporal accessibility by a general transport system,which cannot be used to measure individuals' spatial-temporal accessibility by public transit due to ignore the unique characteristics of the public transit system,such as bus travel time varying in time,tolerable transfer times and access/egress time for one trip,etc.This paper studies on the method for measuring spatial-temporal accessibility by public transit.Firstly,since the bus travel time is varying over time by the influence of the road traffic condition,the public transit system is time-varying.To build a dynamic model for the public transit network,a time-dependent weighted directed graph can be builded,in which each arc's weight representing bus travel time between two adjacent stops along a bus line is extracted based on bus GPS data.Secondly,with the consideration of the limitation to measure spatial-temporal accessibility by public transit for previous algorithms,both transfer times and access/egress time are incorporated into a potential path area algorithm to measure the spatial-temporal accessibility by public transit based on the time-dependent weighted directed graph.Thirdly,supported by the proposed method,a web-based prototype system for measuring the spatial-temporal accessibility by public transit is established with GIS.This system can query travel information,such as a bus station,a bus route,etc,and it can also clearly present the dynamic spatial-temporal constraint faced by an individual within a public transit system.Finally,the proposed method is applied to the bus network of the city of Harbin.The results suggest that this method can effectively measure the spatial-temporal accessibility by public transit operating based on frequency and identify its time-varying characteristics.It is also effective for the public transit operating based on timetable,especially for the case that delay frequently occurs at bus stops due to traffic congestion.Besides,this method can enhance the reality of the spatial-temporal accessibility measure,and it can also reveal the variation of spatial-temporal accessibility by public transit in time dimension,such as different departure time during a day,different departure date and different seasons.