A Sensitivity Based Approach to Network Reliability Assessment

摘要

This paper presents a methodology for evalauting the reliability of transportation networks. While tools already exist to determine the expected benefits of travel demand management or new infrastructure, tools have yet to be developed which take into account disbenefits arising from randomly occurring disturbances. The paper focuses on the sensitivity of both path travel times and expected minimum origin-destination travel times to normal within-day demand and supply variation, where demand variation takes the form of perturbations to origin-destination flows and supply variation takes the form of perturbations to link saturation flows. Two extreme cases are distinguished; one where route choices fully respond to the perturbations, corresponding to the more major, longer-term incident and the other where route choice does not respond, correspodning to the more minor, shorter-term incident. A logit assignment model, referred to as the Path Flow Estimator (PFE), is linearised with respect to the parameters affected by within-day variation, using sensitivity expressions. As analytically derived sensitivities are sometimes difficult to calcualte for large networks, their approximation by finite differencing is considered. Results obtained for a large network (500 links, 8000 OD pairs) in York are discussed, as well as results obtained for a much smaller network (100 links, 60 OD pairs) in Leicester.