It is important that road authorities and policy-makers know what the relation is between road and traffic features and road safety. This project contributes to that knowledge. In this way, research results can provide direction to the discussions about bypasses of the main road network. Relieving the main roads by parallel roads for destination traffic could be safer than extending the main roads with even more lanes. This means improving the safety of lower order roads is necessary.
This project is aimed at finding the relations between, on the one hand, the features of the infrastructure and traffic on the Netherlands road network and, on the other hand, the road safety. It is a continuation and expansion of the project entitled, 'The analysis of crash, road, and traffic features of the Netherlands state roads' (SWOV: R-2002-19). This project takes into account the spatial dependence between road sections (changing routes). The goal is to identify the (non-linear) relation for roads, between the exposure (volume) and crash rate on the one hand, and the crash (and casualties) densities on the other hand; both subdivided by road features.
The preparatory part of the project consists of formulating hypotheses. Examples are: 'an increase in exposure is accompanied by a decrease in crash rate, after which the crash rate remains more-or-less stable, and then increases again'. There is also: 'a route with many variations in volume and road features per vehicle kilometre or per journey time, is accompanied by a greater crash rate than a route with few changes in these features; in accordance with the sustainable-safe philosophy of homogeneity'. The research method (via connected road sections) is closely related to that of time series analyses.
This project begins with a literature study and the formulation of specific hypotheses about relations between the infrastructure's features and exposure/traffic volumes on the one hand, and road safety on the other hand. Next, test areas are selected and the necessary data is gathered to test these hypotheses. In the first place, areas are looked for that have sufficient data about combined routes along motorways and provincial roads. For road safety purposes it is important to include rural, lower order roads in the research. That is where relatively many injury crashes per vehicle kilometre occur. However, there is the problem of there possibly not being enough data for these roads. If, after identifying the necessary data and making an inventory of the available data (mid 2004), it appears that this is not feasible, the project will be conducted on routes with connecting motorways. Although it is true that motorways have a low crash rate, their traffic volumes are increasing rapidly. It is, in any case, known that there is sufficient motorway data to test the hypotheses. After selecting the test areas, the necessary data will be gathered and then analysed, after which the results will be published.