SPIs on Roads

Introduction

There are two SPIs for roads, namely the road network SPI and the road design SPI. The road network SPI indicates whether the actual road category is appropriate given the urban areas that it connects. The road design SPI determines the level of safety of the existing roads. The SPI Manual provides technical information on the calculation of the SPIs for a specific case study area. The Manual also provides a critical discussion of the various steps in calculating the network SPI.

Measurement methods

For the calculation of the road network SPI, the following information is needed:

• Location of urban centres
• Number of inhabitants per urban centres
• Location of roads that connect centres
• Road categories of actual roads
• Length of roads

In practice the calculation proceeds as follows. The locations of urban centres and roads are displayed on (digital) maps. The location of urban centres and the number of inhabitants of these centres are used to produce a list of connections that are assessed. To be able to determine whether the road category is appropriate, the actual road category should be known. Road classifications differ by country and the present classes have to be translated to the road categories specified in the Manual. Finally, the lengths of roads of different categories have to be known in order to calculate the percentage of roads that are of an appropriate category. The data that is needed for the calculation of the network design SPI is available in a digital map (for example MultiNet or TopoNavigator). For most countries, a large percentage of the rural and national roads are included in MultiNet. Thus, MultiNet or any other geographical database seems a good data source to calculate the network design SPI.

The necessary levels of accuracy of the data needed for the calculation of the network SPI are as follows:

• With regard to the number of inhabitants, it has to be determined to which class the urban area has to be assigned.
• Regarding the length of the road, the estimation (in integer or even tens of kilometres) is sufficiently accurate.
• The digital map should be sufficiently detailed to take all roads and all urban centres into account.
• With regard to the road category, accuracy does not play a role, i.e. the assigned road category is either correct or incorrect.
• The data have to be updated once every few (3 to 5) years.

For the calculation of the road design SPI we need the following information:

• EuroRAP Road Protection Score (RPS) per road segment or route
• Road length per road segment or route
• Road category of the current network

EuroRAP designed a method to calculate a final score for a road, expressed with one to four 'stars'. The scores on the several SPIs are weighted to calculate this final score. The magnitudes of these weights are based on accident statistics of a small and arbitrary group of European countries. Possibly these weights should depend on the distribution of accidents types in the country or region, or on the road type, where the RPS is applied. This weighting method should be as transparent as possible. Details of the scoring and weighing methodology are expected to be published soon. For the calculation of the EuroRAP RPS scores per road category, countries are advised to contact EuroRAP.

Inclusion vulnerable road users

Despite the fact that accidents with vulnerable road user are a main crash type, this item is not yet included in the RPS assessments currently being conducted in Europe.

Read more about SPIs for roads in the report Safety Performance Indicators: Theory

Recommendations

The network SPI should be applied in a number of countries in order to investigate whether this SPI is generally applicable. Furthermore, although the results of the case study seem reasonable, evaluating the results of the case study in more detail is recommended, in consultation with the road authority. The specific issues that need further research are among others:

• a more detailed definition of types of urban areas;
• considering the areas' limitations in case of natural barriers or administrative borders;
• the assignment of the theoretically required connections to the actual road network.

Applying the method in various countries is essential for a further evaluation and refinement of the method. Furthermore, the SPIs only assess the safety performance of rural roads and

motorways. Future extension to and adaptation of the model to include urban roads is recommended.