Safety Effects and Cost Benefit of Milled Shoulder Rumble Strips
A Hegewald, Bundesanstalt für Straßenwesen, DE
In the framework of a pilot trial rumble strips have been milled into the shoulders of the German motorway A24. The target behind this measure was to test the effects of rumble strips on the crash figures, especially of crashes caused by fatigue.
In Germany there are each year almost 20,000 crashes with personal injury on motorways, approx. 20 % hereof with running of the road to the right. Besides the loss of control over the vehicle due to inappropriate speed or due to a conflict situation with another vehicle, a major part of these crashes is caused by inattentiveness or fatigue.
In the framework of a pilot trial rumble strips have been milled into the shoulders of the German motorway A24. The target behind this measure was to test the effects of rumble strips on the crash figures on this 35.9 km long route section, especially of crashes caused by fatigue. In order to determine the effectiveness of the rumble strips, a before-and-after investigation with control section (86.7 km) was carried out. The result showed that rumble strips positively affect the severity of the crashes but have only little influence on the crash count. Statistically significant results could be determined for two crash criteria. The number of run-off the road crashes with leaving the carriageway to the right was reduced by 43 % and the number of crashes caused by "other mistakes made by driver" (in Germany usually inattentiveness) was reduced by 34 %.
When calculating the cost-benefit ratio (CBR) it was found that the costs of the measure were relatively small while the benefit on the other hand was very high in terms of the saved crash costs. For a depreciation period of 12.5 years and with the assumption of a constant course of benefit a CBR of 46 was received. Due to this high CBR, the application of milled rumble strips on motorway shoulders is recommended, especially on route sections which show a disproportionally high number of one of the two aforementioned crash characteristics.
Association for European Transport