This report studies the traffic safety effects of four different measures implemented on rural roads in Sweden. The measures investigated are; milled centerline rumble strips on rural 2-lane roads, narrow 2+1 roads with median barrier, divided roads (painted 2+1 roads with median rumble strips) and shoulder rumble strips on motorways. The method used is a before and after study with control group based on crash statistics from the Swedish crash data base Strada. Using a control group, the results have been adjusted for the general road safety trend and changes of traffic volumes. In addition, a limited Empirical Bayes study was done to adjust for regression to the mean. For milled centerline rumble strips on rural 2-lane roads, results show that when regression to mean is considered, the number of fatalities and seriously injured in single-vehicle crashes on road links are reduced by 24 percent (significant), but the number of injury crashes has not changed significantly. Overall, for crash types, the number of fatalities and seriously injured decreased by 15 percent (significant). If regression to mean is not considered, the effects are smaller (-18% for single vehicle crashes) and not statistically significant. For narrow 2+1 roads (9 m wide), the total number of fatalities and seriously injured decreased by 62 percent and the total number of personal injury crashes decreased by 29 percent. Looking only at links (excluding intersections), the number of fatalities and seriously injured decreased by 71 percent and the personal injury crashes by 36 percent. Correcting for regression to the mean gave very similar results. It should be noted that the after period is still short and a continued follow-up is recommended. For almost all of the included road sections, the speed limit was also raised from 90 km/h to 100 km/h when the road was rebuilt to 2+1. No difference in efficiency compared to earlier evaluations of traditional 2 +1 roads (13 m wide) with 100 km/h and 40 percent passing lanes can be observed. In the case of divided roads (painted 2+1 roads with median rumble strips), results show that when regression to mean is considered, the number of fatalities and seriously injured on road links are reduced by 44 percent. If regression to mean is not considered, the effects are smaller (-29%) and not statistically significant. For shoulder rumble strips on motorways, the results show that the total number of killed and seriously injured decreased by 16 percent and the number of fatalities and seriously injured in single-vehicle crashes decreased by 25 percent. Correcting for regression to the mean gave very similar results. In conclusion, all four studied measures have shown positive traffic safety effects and reduce the numbers of killed and seriously injured on rural roads. However, for narrow 2+1 roads the empirical crash statistics used in the study is limited and a continued follow up is recommended. (Author/publisher)
Abstract