Travel time cost functions for urban roads: a case study in Italy

Abstract

This paper describes how cost functions are commonly used in traffic assignment in order to account for the effects of congestion on road link performances. Despite their influence on assignment results, not many effective functions are available for urban roads. Indeed, the effects of congestion on the travel time required to cross an urban link have often been considered negligible in comparison with those on delays at intersections. Nonetheless, traffic flow disturbances like side-parking can appreciably affect link travel time with the rise in congestion, especially in the roads of ancient centers in historical cities. Hence this paper presents a travel time function for urban road links that includes the effect of side-parking, secondary streets and road winding on the worsening of performance due to congestion. Model parameter identification was based both on empirical and experimental data, the latter having been obtained by means of a calibrated micro-simulation model. Cross-validation results do not exclude the possibility of applying the proposed function to different urban areas.