Abstract: In order to analyze the impact of freeway three-dimensional spatial alignment continuity decline on traffic safety, this paper collected and statistically processed the alignment data and accident data of five interstate freeways in Washington State, USA from 2011 to 2018. The freeways were segmented with 100 meters length as the fixed length unit. The average spatial curvature of each unit (ASC), the absolute value of the curvature difference with the previous adjacent freeway unit(AVDP), and the absolute value of the curvature difference with the next adjacent freeway unit(AVDN) were calculated as descriptive variables, and the number of freeway unit accidents was used as the described variable. The traditional negative binomial model, zero-inflated negative binomial model, and zero-truncated negative binomial model were used to perform fitting analysis on all freeway units data and the freeway units data where accidents occurred. The results show that: the negative binomial model fits better than the zero-inflated negative binomial model based on all units data; the zero-truncated negative binomial model fits better than the negative binomial model based on the accident-occurring units data. In the four models, there is a large positive correlation between the absolute value of the curvature difference of the adjacent freeway unit and the safety level of the freeway unit, that is, increasing the continuous performance of the three-dimensional curvature of the freeway can improve the traffic safety level. It indicates that AVDP and AVDN can be used as a freeway alignment level evaluation index to provide support for the optimization of freeway alignment design.

Key words: traffic accident, freeway, three-dimensional alignment, continuity, regression model