Li Lingyu, Gayah Vikash V, Donnell Eric T
Department of Civil and Environmental Engineering, The Pennsylvania State University, 231 Sackett Building, University Park, PA 16802, United States.
Accid Anal Prev. 2017 Nov;108:343-353. doi: 10.1016/j.aap.2017.08.035. Epub 2017 Sep 23.
The American Association of State Highway and Transportation Officials' Highway Safety Manual (HSM) contains safety performance functions (SPFs) to predict annual crash frequencies for several roadway types. When applying these SPFs in a jurisdiction whose data were not used to develop the SPF, a calibration factor can be applied to adjust the expected crash frequency estimate to statewide or local conditions. Alternatively, the HSM suggests that transportation agencies may develop their own SPFs in lieu of applying the calibration factor to the HSM SPFs. However, the HSM does not provide guidance on the appropriate level of regionalization that should be adopted for either method, even though safety performance may vary considerably within a state. In light of this, the present study considers the development of local or regionalized SPFs for two-lane rural highways within the Commonwealth of Pennsylvania. Three regionalization levels were considered: statewide, engineering district and individual counties. The expected crash frequency for each level of regionalization was compared to the reported crash frequency over an eight-year analysis period. The results indicate that district-level SPFs with county-level adjustment factors provide better predictive accuracy than the development of a statewide SPF or application of the HSM-calibrated SPF. The findings suggest that there are significant differences in safety performance across engineering districts within Pennsylvania. As such, other state transportation agencies developing SPFs or using calibration factors may also consider how variations across jurisdictions will affect predicted crash frequencies.
美国州公路和运输官员协会的《公路安全手册》（HSM）包含安全性能函数（SPF），用于预测几种道路类型的年度事故频率。在一个未使用其数据来开发SPF的辖区应用这些SPF时，可以应用一个校准因子，以将预期事故频率估计值调整到全州或当地的情况。或者，HSM建议运输机构可以开发自己的SPF，以代替对HSM的SPF应用校准因子。然而，HSM并未就这两种方法应采用的适当区域化水平提供指导，尽管一个州内的安全性能可能有很大差异。有鉴于此，本研究考虑为宾夕法尼亚州的双车道农村公路开发本地或区域化的SPF。考虑了三个区域化水平：全州、工程区和各个县。在八年的分析期内，将每个区域化水平的预期事故频率与报告的事故频率进行了比较。结果表明，带有县级调整因子的区级SPF比开发全州范围的SPF或应用经HSM校准的SPF具有更好的预测准确性。研究结果表明，宾夕法尼亚州各工程区的安全性能存在显著差异。因此，其他开发SPF或使用校准因子的州运输机构也可能需要考虑辖区间的差异将如何影响预测的事故频率。
