In this project, rut depth development studies were carried out on road sections subjected to three specific types of traffic safety measure. The measures, implemented through the Swedish Transport Administration’s "Safe accessibility" project, included milled centreline rumble strips, narrow 2+1 roads with median barrier, divided roads (painted 2+1 roads with median rumble strips). The introduction of centreline rumble strips and barrier separation can result in traffic confinement and cause a reduction in the amount of vehicle lateral wander. This reduction is likely to increase the rate of rutting. The purpose of this study was to investigate how annual rut development rates and rut area measurements — on conventional 2-lane roads with milled centreline rumble strips, narrow barrier separated roads and divided roads — were affected by the introduction of these safety measures. With regards to centreline rumble strips and comparisons between the test and control sections, results indicated that there were sometimes differences in the rut development rates. However, these differences were usually very small and inconsistent. The conclusions that can be drawn from the results are that centreline rumble strips do not have a confining effect on traffic and have no adverse effect on the rate of rutting. For narrow barrier separated roads and divided roads, results indicated that, for AADT levels (AnnualAverageDailyTraffic) between 1,000 and 4,000 vehicles per day, the average annual rut depth growth (SDM17) was 0.66 millimetre for barrier separated roads, 0.48 millimetre for divided roads, and 0.57 millimetre for conventional roads. Rut depth development rates increased with AADT for all road types. For AADT levels greater than 8,000 vehicles per day, the SDM17 was 1.19 millimetre for barrier separated roads, 1.25 millimetre for divided roads, and 0.95 millimetre for normal roads. 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. Comparisons between divided roads and conventional roads only showed higher SDM17 rates for AADT levels greater than 8,000 vehicles. 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. The confining effect of barrier separated roads can also be confirmed by lateral position measurements. Measurements have revealed that the standard deviation of lateral position was considerably lower when compared to values for normal roads with the same width. (Author/publisher)
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