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Urban Björketun

This report studies the traffic safety effects of four different measures implemented on rural roads in Sweden. The measures investigated are:

  1. milled centerline rumble strips on rural 2-lane roads
  2. narrow 2+1 roads with median barrier
  3. divided roads (painted 2+1 roads with median rumble strips)
  4. 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.

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. 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.

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.

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