Safety Assessment of Routes in a Regional Network

This paper describes how the concept “Sustainably-Safe Traffic” is the leading vision in road safety policy and research in the Netherlands. The main goal of a Sustainably-Safe road transport system is to reduce the annual number of road accident casualties to a fraction of the current levels. Important requirements following from this vision are that trips should follow safe roads as much as possible, trips should be as short as possible, and the quickest and safest route should coincide. Modeling route choice will provide answers to the planning issues of Sustainably-Safe Traffic, however, the safety effects of these requirements is a totally different issue that needs to be dealt with. This paper focuses on the design of a method that enables the planner to find out the safety effects of existing route choice, and also, changes in route choice. A description of road safety can be made in various ways. When using a microscopic model, conflicts between vehicles will be an integral part of the simulation. The best-known safety indicator in this type of model is the ‘conflict’ situation, a situation where two vehicles are approaching each other and where, if no action were taken a crash would occur. These conflict situations are detected in the micro-simulation model and do not necessarily relate directly to any actual observed conflicts. The traffic safety assessment is carried out by quantifying the safety level of a route on the basis of certain characteristics that define the route and that are assumed to be related to safety. According to earlier work of the authors, detected conflicts in a micro-simulation model appear to be significantly related to observed crashes. This paper aims at assessing safety levels of routes by using conflicts as a surrogate measure of (un)safety. The paper examines the quantitative relationship between the conflicts at junctions encountered by vehicles traveling along a route on the one hand and the assessment of the route’s safety level on the other. The latter is obtained from route characteristics such as travel time, route length, number of left turns, distance traveled on main roads and number of road categories within a route.