In Sweden, it is today regulated that winter tyres must be used on the drive axle of heavy vehicles (total weight in excess of 3,500 kg) during the winter season period, December 1 to March 31, in case of winter conditions. This requirement is based entirely on accessibility, and it is considered that winter tyres on the drive axle provides better conditions for heavy vehicles to go forward in icy and snowy conditions. Previous accident risk studies have not been able to demonstrate that the use of winter tyres instead of summer tyres for heavy vehicles in winter could lead to reduced risk of accidents. In Norway and Finland, the regulations on tyre use for heavy vehicles in winter time has recently been revised. Prior to a discussion of possible regulations in Sweden on winter tyres also on other axles, there is reason to update the previous accident risk studies. The purpose of this study has been to calculate the risk of accidents on ice/snow conditions for comparison between summer and winter tires for heavy trucks. The study was performed according to the method previously used in the VTI studies conducted in 2000 and 2008. This meant that two questionnaires were sent out by the end of the winter 2015/2016. One survey to analyse the vehicle mileage on ice/snow conditions with different combinations of tires, and one questionnaire directed solely to the vehicle owners whose vehicles according Strada during the winter season have been involved in an injury accident. Accident risk calculations were limited to vehicles with a total weight of 16 tons. From 2000 exposure questionnaires sent out, 648 responses were received. During the period from December 2015 to March 2016, 215 personal injury accidents occurred with Swedish-registered vehicles with total weight of 16 tonnes or more. Questionnaires were sent to the owners of all these vehicles and 39 responses were received. Based on the exposure survey we can conclude that a very large proportion of heavy goods vehicle traffic volume consists of vehicles with winter tyres on both steering and drive axle. The share is about 90 percent, compared with just under 50 percent of the buses in the study of 2008, and an estimated 25—50 percent for heavy trucks in the study of 2000. In the exposure survey as well as the accident survey, the marking M + S was used as a criterion for a winter tyre on the steering axle, which then also come to include some tyres that are not approved winter tires. The extent to which this leads to an overestimation of the proportion of winter tires on the steering axle is difficult to estimate. The high proportion of winter tyres on both axles leads to very few accidents occurring with summer tyres on the steering or drive axle, which makes it difficult to estimate the relative risk of accidents for those choices of tyres. With the few accidents survey responses received in the survey, it has only been possible to estimate the relative risk of accidents for the combination of winter tyres on the steer and drive axles. The relative risk of accidents for driving on ice/snow road conditions compared to bare ground was 1.38, which is consistent with the previous study of buses (Hjort et al 2008). Because of the low response there has not been possible to divide vehicles into those with and without a trailer, to study the trailer tire’s impact on accident risk. Based on the results from the questionnaire responses of the examined winter, it was judged that additional questionnaires sent out the winter 2016/2017 would probably not provide enough new material for estimating the risk of accidents also for summer tyres on steering and trailer axles. It was therefore decided to end the study after one winter. (Author/publisher)
Abstract