The number of crashes observed in naturalistic driving studies is typically small; thus, there is a need to use crash surrogates. This study evaluated the use of near-crashes as a surrogate measure when assessing the safety impacts of driver behaviors and other risk factors. Two metrics, the precision and bias of the risk estimation, were used to assess whether near-crashes could be combined with crashes. The principles and exact conditions for improved precision and unbiased estimation were proposed and applied to the 100-Car data. The analyses indicated that, in general, there is a strong relationship between the frequencies of contributing factors for crashes and for near-crashes. The study also indicated that analyses based on combined crash and near-crash data consistently underestimate the risk of contributing factors compared to using crash data alone. At the same time, the precision of the estimation will increase. This consistent pattern allows investigators to identify the truly high risk factors while qualitatively assessing the potential bias. In summary, the study concluded that there is a benefit to the use of near-crashes as a crash surrogate for risk assessment when naturalistic studies are not large enough to generate sufficient numbers of crashes. (Author/publisher)
Samenvatting