Speed-reducing measures for 80 km/h roads

Control of driving speeds offers an important possibility to improve traffic safety on rural 80 km/h roads. An experimental project in Drenthe was aimed at the development and testing of measures that effectively reduce speed without significantly reducing driving comfort up to speeds of 80 km/h. First, some variants of proposed infrastructural measures were tested in a driving simulator before actual application. Secondly, a resulting set of four basic design elements was implemented on four 80 km/h road sections in Duated in terms of the actual driving behaviour, including both speed and lateral placement. Results of the simulator study reveal that a narrow lane width (2.25 m + 0.70 m profiled edge strip) compared with a normal lane width (2.75 m + 0.20 edge area) gives the largest speed reductions and is fairly resistant to effects of adaptation. Moreover, the narrow lane width especially reduces the speeds of drivers under time-pressure, implying that also in practice speed variance may be reduced.
The evaluation of the resulting set of measures on four test locations in Drenthe, based upon the analysis of inductive loop data, indicated that a sustainable speed reduction of about 2 km/h was achieved. Video-observations revealed that, in spite of the reduced width of smooth asphalt, the 0.30 m central chipping strip marking (instead of 0.10 m conventional central marking) results in a lateral placement of minimally 0.10 m away from the centre of the road. Apparently, drivers refer mainly to ther mainly to the near-by side of the central marking. Over a two-year period a 20% reduction in the number of accidents was reached, whereas at control locations an 8% increase occurred.