At the VTI (Swedish National Road and Transport Research Institute), researchers investigated 36000 accidents resulting in light to serious injuries between 2007 to 2011. Of these, 77% were single vehicle accidents, 12% were accidents involving bicycles and motor vehicles, and in 7% cyclists collided with each other. Besides the large number of head injuries, the number of hip injuries also stood out. According to the Swedish researchers many of the cyclists with serious head injuries were not wearing a helmet, and according to VTI this justifies the recommendation to wear cycle helmets. Slipperiness caused by snow and frost turned out to be the most important cause of single vehicle accidents in Sweden. Collisions with road curbs took second place. In general, proportionally more accidents occured on poorly maintained roads. Also in Sweden investigators complain about the sparse police documentation of single vehicle accidents. For that reason this research was based on hospital records.