Safety Assessment of Routes in a Regional Network
P Marchesini, A Dijkstraboth, SWOV Institute for Road Safety Research, NL
This paper aims at assessing safety levels of routes in a network. It shows the relationship between the conflicts encountered by vehicles travelling along a route on the one hand and the assessment of the route?s safety level on the other.
In the Netherlands, the concept 'Sustainably-Safe traffic' is the leading vision in road safety policy and research. 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 on 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. Modelling 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 which need to be dealt with. This paper focuses on the design of a method which 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 in which 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. It examines the quantitative relationship between the conflicts (at junctions) encountered by vehicles travelling 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 travelled on main roads and number of road categories within a route.
Different routes in a regional network which were travelled by the modelled vehicles were used for the analysis. Initially nine characteristics of a route defined the level of safety. The statistical analysis will demonstrate which characteristics are the most relevant to quantify the level of safety. This method of quantifying the safety level of routes will allow evaluating road network structures from a safety perspective. It is expected that by optimizing the design of the network and by influencing route choice a (more) sustainably safe traffic system can be sought. Ultimately, this method will provide road authorities and traffic engineers with a tool by which they can include traffic safety in the planning and design phase of a project.
Association for European Transport