Milled rumble strips make roads safer

A study by the Swedish Road and Transport Research Institute VTI shows that milled rumble strips at the centre of a two lane road are probably an excellent measure to reduce the number of head-on collisions which occur because tired and inattentive drivers inadvertently leave the lane they are driving in.

The study shows that one of the effects of milled rumble strips at the centre of the road is to make car drivers reduce their speed and keep further away from the centre of the road.

Milled rumble strips have been found to work well on Swedish roads which are not wide enough to have a central barrier such as a wire rope barrier. However, no effects have been found which cause changes in the behaviour of the drivers of heavy vehicles.

“Milled rumble strips help drivers through both the noise they experience and the vibration that is set up in the vehicle, the seat and the steering wheel. These signals may prevent drivers from inadvertently driving over the centre line because they are tired or their attention is distracted,” says Anna Anund, a researcher at VTI.

Results from the study

* According to drivers, the greatest advantage of the milled rumble strips is that they warn drivers that they are, inadvertently, about to drive over the centre line (94%).

* Car drivers significantly reduced their speed by an average of 1.8 km/h at all survey positions.

* On average, car drivers drove 5 cm nearer the edge of the road when the road had milled rumble strips than when there were no rumble strips.

* 76% of the drivers replied that they would feel safer if there were rumble strips at the centre of the road.

* 83% said that they would feel safer because the strip would prevent them from inadvertently driving into the wrong lane.

* 88% thought that milled rumble strips are a good way to increase road safety.

The strips may also improve driver behaviour by making drivers decide not to cross the centre line on sections of the road where doing so is incompatible with road safety. In turn, this may cause a reduction in the number of overtaking and curve cutting manoeuvres.

The rumble strip selected for the study has been named the ’Målilla strip’. The strips have been milled at 1.2 m centres. They are 35 cm wide, 15 cm long and about 1.0 cm deep. The test section is on Highway 34 between Målilla and Hultsfred, and its length is14 km. The strips have been evaluated by traffic surveys, roadside interviews and observations.