Injury severity analysis of rural vehicle crashes involving familiar and unfamiliar drivers

Familiar and unfamiliar drivers may exhibit different behaviours in response to the road environment. Overall familiarity with the road environment is a human factor believed to play a role in road crash injury severity due to its effect on a driver's decision-making process, reaction time, etc. Hence, there is a need to separately analyse familiar and unfamiliar drivers regarding the injury severity of crashes. Using a six-year database of 30,481 rural two-vehicle crashes in Guilan province, Iran, this research first defined four categories of crashes, reflecting various levels of the involved drivers’ familiarity with the environment (72% of drivers were from the same vs. 28% from a different province). Next, the injury severity of crashes in each familiarity crash category was analysed using both non-parametric (classification and regression trees) and parametric (logistic regression) methods. When both crash parties were unfamiliar, several results are different compared to when both parties were familiar or when ignoring driver familiarity. For instance, young at-fault drivers increased the injury severity of crashes if they were unfamiliar, while they decreased the crash severity if they were familiar. Also, crashes in winter tended to be more severe when one or especially both crash parties were unfamiliar, but winter crashes were less severe when both drivers were familiar or when driver familiarity was ignored. Overall, when both drivers were familiar, 63% of crashes were injury/fatal; however, when both drivers were unfamiliar, only 31% of crashes involved an injury or fatality.