Road safety on federal motor­ways

In terms of mileage, federal motorways are considered as particularly safe roads. However, on no other roads in Germany are so many injuries registered per kilometre by road traffic accidents. Accidents in longitudinal traffic are particularly frequent on motorways, especially collisions with vehicles driving ahead or waiting. Around 40 percent of accidents involving fatalities occur in the dark.

The approximately 13,000 km of federal motorways (2% of the entire German road network) account for almost one third of the total mileage of motor vehicles registered in Germany. In terms of mileage, federal motorways are considered to be the safest roads in Germany compared to rural and urban roads. However, with a total of 2,500 injuries per 1,000 kilometres and 32 fatalities per 1,000 kilometres, they have the highest density of accidents on roads outside built-up areas. Accidents in longitudinal traffic and driving accidents are particularly characteristic for the accident occurrence on federal motorways. For this reason, the German Insurers Accident Research (UDV) initiated a research project and carried it out in cooperation with SHP Ingenieure. The aim of this research project was to identify and quantify the infrastructural, operational and traffic-related factors influencing road safety on federal motorways.

The main results of the research project can be summarised as follows:

Accident analysis

  • Accidents in longitudinal traffic (61 %) and driving accidents (26 %) dominate the accident occurrence on motorways. Men cause about 70 % of the accidents of these two accident types. The most serious accidents are caused by goods vehicles, especially in collisions in longitudinal traffic.
  • The most frequent kinds of accidents include collision with a vehicle driving ahead or waiting (45%), collision with a vehicle driving sideways in the same direction (14%), leaving the lane to the right (17%) and to the left (13%).
  • Inappropriate speed (35 %), insufficient safety distance (34 %) and overtaking errors (about 9 %) are the most frequent causes of accidents (multiple answers possible).
  • About 40 % of accidents with fatalities on motorways occur in the dark. For the other roads (i.e. rural and urban roads together), the figure is only about 28 %.
  • Road condition (dry, wet/damp or winter slippery) does not seem to have any influence on the degree of injury by accidents on motorways.

Infrastructure design

  • Sections with medium curvatures (between 10 gon/km and 30 gon/km) tend to be safer than sections with very low or too high curvatures.
  • In the case of curve radii between 3,000 m and 6,000 m in the course of two-lane directional carriageways, the accident cost rates and the probability of accident concentrations are the lowest.
  • In ramps, medium radii (80 m to 125 m) tend to have a low accident cost density.
  • Entrance types E 1 and E4 according to the Guidelines for the Design of Motorways (RAA) are particularly favourable in terms of accident cost density.
  • Exits with lane subtraction according to RAA are clearly less favourable than the other types of exits.
  • No statistically reliable influence on traffic safety was found for the following parameters: Undulations, hilliness, longitudinal gradient, traffic intensity, maximum permitted speed.
  • This also applies to combinations investigated (e.g. speed limit with average daily traffic (DTV) or with curve radius).

Further information on the study conducted on "Road safety on German motorways" can be found at:

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