Road safety on motorways

Søren Underlien Jensen, February 2018

This publication describes safety performance functions, accident modification factors, and so on for the safest motorways in Europe, i.e. motorways in Denmark.

Safety performance functions have been estimated for five segment types; motorway link, exit diverge, entrance merge, exit ramp and entrance ramp. A safety performance function describes relationships between road safety and exposure for a very specific variant (specific road design and traffic regulation) of the segment type leading to almost causal relationships between safety and exposure.

More ordinary accident prediction models have been estimated for ten other segment types on the motorway network.

Accident modification factors describe how road safety changes as road design or traffic regulation is altered. Combining safety performance functions and accident modification factors enables planners to estimate expected numbers of accidents and injuries for most parts of the motorway network.

The publication also includes a user manual for a calculation tool, which may estimate expected numbers of accidents and injuries for all 15 segment types. The accident modification factors are part of this tool, so the user may alter the design of the motorway or ramp, and see how this affects safety. The tool includes conversion factors so e.g. injuries are split into killed, severe injuries and slight injuries. The lastly, the tool also includes year factors enabling estimations to be for specific year(s).

Link to publication: Road safety on motorways

Link to calculation tool: Spreadsheet

Link to Danish report: Uheldsmodeller, sikkerhedsfaktorer og værktøjer for strækninger – Motorvejsnettet