This report consolidates evaluations performed within the project “Safe accessibility” on behalf of the Swedish Transport Administration. Four different measures implemented on rural roads in Sweden with the aim to increase traffic safety and improve accessibility are investigated. For milled centerline rumble strips on rural 2-lane roads, the number of fatalities and seriously injured in single-vehicle crashes on road links were 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). As regards rut depth development, the conclusions are that centerline rumble strips do not have a confining effect on traffic and have no adverse effect on the rate of rutting. A study about the effects and consequences of different types of milled rumble strips showed that there are no known arguments for not using the sinus rumble strips. However, further studies on the impact of drivers of heavy vehicles are recommended, but also new measurements of external noise to make calculations of how close to living rumble strips may be used, without guideline values for noise exceeded. Finally, there is a need for shoulder rumble strips on motorways, the results show that the total number of killed and seriously injured decreased by 12 percent and the number of fatalities and seriously injured in single-vehicle crashes decreased by 25 percent when correcting for regression to the mean. 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. As regards rut depth development, in comparison with ordinary road types, it can be concluded that for AADT levels greater than 8,000 vehicles, the annual rut depth development rate is about 25 percent higher for barrier separated roads. With lower AADT levels, differences reduced to between 10—15 percent. With regards to barrier separated roads, a clear effect of vehicle confinement can be seen for all levels of traffic volume. Rut depth growth is consistently higher than that associated with conventional roads. Studies of the effect on traffic efficiency showed that the proportion of HGVs is an important factor to consider in the design of narrow 2+1 roads. 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. As regards rut depth development, the results indicated that, for AADT levels between 1,000 and 4,000 vehicles per day, the average annual rut depth growth (SDM17) was 0.48 mm for divided roads and 0.57 mm for conventional roads. Rut depth development rates increased with AADT (AnnualAverageDailyTraffic) for both road types. (Author/publisher)
Abstract