The need of spillback simulation in assessing robustness: concepts and a case study with dynamic route choice

Robustness of a network is, as main aim for road network managers these days, becoming an important study area for transportation scientists now. This paper discusses one specific aspect of robustness: the consequences of the blocking of a link in a road network using a traffic simulator. In a regional size road network simulation study, sequentially links are blocked and the simulation program determines the network performance, both with a route choice adapted to daily congestion and a route choice adapted to the actual situation. The paper focuses on spillback effects. A special feature in the new simulator proposed here is that the representation of spillback can be switched on and off; thus, effects of spillback can be examined explicitly. Road network robustness and characteristics of vulnerable links are evaluated for both spillback and non-spillback cases. It is found that spillback simulation is necessary for the estimation of the robustness of the network as a whole. Simulation of spillback is also needed to assess the impact of the blocking of a specific links; furthermore, without simulating spillback, it is not possible to identify correctly the most vulnerable links for the network performance.