Assessing Road Network’s Disruption Due to Climate Change - Testing a Methodology Based on Static Traffic Assignment Model



Assessing Road Network’s Disruption Due to Climate Change - Testing a Methodology Based on Static Traffic Assignment Model

Authors

Michael SAVARY, CEREMA/DTerNC, Thomas ANSELME, CEREMA/DTerNC, Francois COMBES, CEREMA/DTecITM

Description

This study aims to design a methodology to assess the importance of transport links in a road network. It examines the impact of disruptions (which could be consecutively to climate change) on travel demand on the basis of a static assignment model.

Abstract

The impacts of climate change on transport networks will most probably get more severe during this century. Transport systems play a major role in the economy, and are, for many of them, highly sensitive to extreme weather. In order to prepare the necessary improvements of infrastructure resistance and resilience it is necessary to analyse their vulnerability and importance.

In an infrastructure network, some links are more sensitive to disruptions than others, in the sense that their disruption will have a larger cost in terms of increased trip lengths and durations, and congestion. Also, there are other links which, without being vulnerable themselves, contribute to the overall network’s robustness: if those links weren’t there, the disruption of other vulnerable links would have far more stringent repercussions.

The objective of this study is to design a methodology to assess the importance of transport links in a transport network. This study is focused on the road network. It examines the impact of disruptions on travel demand in a medium term perspective (i.e. after drivers have adapted their route choices, but before they change mode or destination) on the basis of a static assignment model. Impacts in terms of damages and injuries are outside the study’s scope. The study proceeds in three main steps, described below.

The first stage gives the intuition of the problem, on the basis of a simple example: that of the disruption of a particular highway link in the French urban area of Rouen. Its consequences are presented and discussed in detail, with a large range of indicators such as travel time variation, generalised cost increase, and accessibility changes. Other examples are also discussed; a selection of indicators is kept for the following stages, on the basis of this discussion.

The second stage presents a methodology to estimate systematically the importance of the components of a given road network. The methodology is as follows: for a given road network, a selection of links is made. For each of these links, travel demand is assigned, with the selected link disrupted. Global performance indicators (travel time, transport cost, etc.) are retrieved, in order to compare the importance of each of the examined links. A specific algorithm was developed to proceed to these simulations automatically. The methodology is applied to the urban area of Rouen, and to the interurban road network of a larger area set in the North-West of France. In both cases, several hundred simulations were achieved. Note that this methodology requires the availability of a traffic assignment model. An alternative method, based on multi-criteria analysis, will be presented, for cases were no such model is available.

The objective of the study’s third stage is to assess the contribution of specific road links to the overall network’s robustness. Those links are identified as follows: during the simulations achieved in the previous stage, the traffics on all the non-disrupted links are registered. If some links accommodate substantial traffic increases in a significant amount of disruption scenarios, it probably means that they contribute strongly to the overall’s network robustness, and that they should be specifically protected and even reinforced, in order to improve globally the network’s robustness.

Publisher

Association for European Transport