Alan M. Voorhees Transportation Center, Edward J. Bloustein School of Planning Public Policy, Rutgers University, New Brunswick, NJ, United States.
Alan M. Voorhees Transportation Center, Edward J. Bloustein School of Planning Public Policy, Rutgers University, New Brunswick, NJ, United States.
Accid Anal Prev. 2018 Sep;118:29-37. doi: 10.1016/j.aap.2018.05.017. Epub 2018 May 31.
Transportation planners and traffic engineers are using crash modification factors to evaluate how changes in road geometry and design features can reduce crashes. Crash modification factors are typically estimated based on segmenting links on a highway and associating with geometric features. This allows statistical methods to be applied to the data. Concurrently there is a stream of research that relies on spatial units of analysis to examine crashes; these typically use broad features of the road network combined with socio-economic and demographic factors that are associated with crashes. In this paper, we examine whether omission of these spatial factors in a link-based model results in mis-specified models, in particular, omitted variable bias. Our results suggest that there is no change in coefficient signs, but that there is a reduction in the magnitude of estimates, suggesting that omitted variable bias exists. The sign of spatial variables differ substantially when combined with a link-based model. We also find substantial variability in coefficient estimates, and discuss the implications of these results for the use of crash modification factors in cost-benefit analysis of road safety projects.
交通规划者和交通工程师正在使用碰撞修正因子来评估道路几何形状和设计特征的变化如何减少碰撞。碰撞修正因子通常基于高速公路上的链路分段并与几何特征相关联来估计。这允许将统计方法应用于数据。同时，有一系列研究依赖于空间分析单元来检查碰撞；这些通常使用道路网络的广泛特征以及与碰撞相关的社会经济和人口统计因素。在本文中，我们研究了在基于链路的模型中忽略这些空间因素是否会导致模型指定不当，特别是忽略变量偏差。我们的结果表明，系数符号没有变化，但估计值的幅度减小，表明存在忽略变量偏差。当与基于链路的模型结合使用时，空间变量的符号会有很大差异。我们还发现系数估计值存在很大的可变性，并讨论了这些结果对道路安全项目成本效益分析中使用碰撞修正因子的影响。
