Vägparametrar och deras inverkan på trafiksäkerheten : Fallstudie på länsväg 360 Lycksele - Vilhelmina

Sammanfattning: The interaction between the driver, the car and the road is essential for the road safety. This case study focuses on the road condition and its effect regarding road safety issues. By studying and isolating the road condition aspect and its contributing role to the accident occurrence, the aim is to explore their relationship, as well as highlight the road parameters that are commonly associated with accident occurrence. This result will be used to develop and increase awareness of the impact of poor road alignment and poor road surface conditions on traffic safety, in order to prevent these accidents from occurring. The road parameters chosen for this study include side friction, cross slope and rut bottom cross slope, road texture, curvature, drainage gradient and rutting. The case study was limited to lv 360 in Västerbotten, where all accidents with an unclear cause of the accident were studied, between 2003 and 2012 were carefully studied and assessed based on the condition of the road at the time of the accident. The study was based on accident data from Transportstyrelsens accident database STRADA and road data was obtained from Vecturas Profilograf. Analysis of the various road parameters and their respective safety limits, identified many hazardous sections on lv 360. Low side friction values, insufficient drainage gradient and incorrect cross slopes are some of the shortcomings that were found. The results show that 70% of all accidents occurred on curves where the vehicle either skidded or went off the road. Furthermore, the results show that the side friction demand in 65% of the accidents far exceeded the designed side friction supply according to VGU. Insufficient side friction associated with curves shows an evident relation with the accident occurrence. The analysis shows that 80% of the accidents had deficiencies in two or more road parameters. Improperly designed cross slopes in curves – where the slope instead of resisting the lateral force, contributed to it – was found to create dangerous circumstances for the traffic. These were also found at lv 360, why the cross slope design according to the results, directly affects the accident rate – particularly at curves. Improper cross slope in sections where the gradient is low often result in insufficient drainage gradient, and consequently a high skid risk. These were common on entry and exit points of curves, where the cross slope shifts between straight sections and curves and thus passes zero. The results show that the drainage gradient in 70 % of the accidents was too low and in many cases fell below VGU's requirement of 0.5 % before and after the curve.