Measuring Accessibility To Public Transit Stops Under Travel Time Uncertainty

As an important part of urban transportation system,the development and optimization of public transportation system is of great significance to alleviate traffic congestion,air pollution and other problems in cities.Public transit accessibility is a key index to measure the service capacity of urban public transportation.The existing public transit accessibility measures can be divided into “Accessibility to Transit Stops(TTA)” and “Accessibility by Transit(BTA)”.TTA refers to the ease of arriving public transit stops from a specific location.In contrast,BTA measures the convenience of finishing a specific activity by transit from a specific location.Both of TTA and BTA can reflect the service quality of public transportation system,and they interact with each other to some extent.However,most existing research on TTA and BTA are usually independent.Particularly,the impact of accessibility to services by transit is almost never considered in the research on TTA.In addition,existing studies show that travel time uncertainty has a crucial impact on humans’ travel behavior.However,the traditional research on TTA does not involve the travel time by public transit,thus the gaps of reliability between bus and subway cannot be revealed.Therefore,the main contents and results of this paper are as follow:(1)An accessibility to transit measure based on station efficiency is proposed,in which the characteristics of both TTA and BTA are considered.The concept of station efficiency is put forward integrating three factors: the number of stations that can be reached,the travel time to,and the difficulty of obtaining other urban services from destination stations,which quantifies the convenience of getting other city services from a public transport station(i.e.,BTA).The supply-demand ratio of transit stations is used to characterize the ease for urban residents to arrive transit stops(i.e.,TTA).(2)An accessibility to transit measure in the environment of travel time uncertainty is further proposed,which extends the proposed TTA measure mentioned above by introducing the concept of travel time reliability.Considering the uncertainty information of public transit travel time,transfer waiting time,etc.,the method of accessibility to transit stops under reliability constraint is constructed.(3)A case study in Shenzhen city is carried out.Experiment results show that the traditional TTA measurement ignores the influence of BTA,which may underestimate the accessibility to transit stops for urban residents in areas with densely-packed transit stations and routes,and overestimate the accessibility to transit for urban residents in areas with sparsely-packed transit stations and routes.In addition,The empirical results also show that ignoring travel time uncertainty may overestimate the accessibility to transit stops of urban residents all around the city.However,it has a greater impact on urban residents’ accessibility to transit stops in areas with densely-packed transit stations and routes than those in areas with sparsely-packed transit stations and routes.