Safety Performance Functions for Two-Lane Urban Arterial Segments

Abstract

This paper presents the safety performance function calibration and development process for the undivided two-lane urban and suburban arterial segments in New Jersey. Data requirements, the availability of required data, and the data processing and extraction methods are presented, along with detailed results of the calibration and development process. Negative binomial, Poisson, zero-inflated Poisson and Hurdle models were generated using the development database. The best model fit were based on likelihood ratio test, AIC and BIC statistics, and rootograms. The test database was used to calculate the calibration factor for U2 segments. The prediction of the generated models were then evaluated and compared to those of calibrated highway safety manual model, using the test dataset. The results showed that the negative binomial and hurdle models yield nearly 10 percent improvement in average absolute residual statistic. This paper also shows the impact of crash location information on analyses results, and underlines that efforts made to manually extract the missing required data can easily be offset by the inaccuracies in crash frequency databases, and the thresholds used to identify intersection related crashes.

Keywords: safety performance functions, highway safety manual, generalized linear models, urban arterials, calibration factor