Effect of tyre tread depth on accident involvement during summer in Finland

The aim of the paper is to determine whether various tyre tread depths in passenger cars and vans were associated with different fatal accident involvement rates or different weather distribution of fatal accidents. Data used in this study includes fatal accidents in 2000–2007 reported by Finnish road accident investigation teams, and tyre check data from annual tyre safety campaigns. The risk of being responsible for a fatal crash for drivers having an illegal tread depth of less than 1.6 mm is three times as high as for those having a tread depth of 3.5 mm or above. Among drivers less responsible for a crash, the risk of the being involved in a fatal crash was similar or slightly lower with a low tread depth than with a higher one. However, there are behavioural factors that correlate with the tyre tread depth. Accident involvement risk in relation to tread depth will be compared with compliance with the main traffic rules (e.g. use of seatbelts, exceeding the posted speed limits and driving while intoxicated). Among drivers who complied with the main traffic rules, those with a tread depth below 1.6 mm were just 20 % more likely to be involved in fatal crashes than those with a depth of 3.5 mm or more. Consequently, the main results imply that drivers should be informed about the importance of tyre depth as a part of their general driver training, even if the increase of risk due to low tyre tread depth is not as high as often considered.