Effects of Highway Geometric Features and Pavement Quality on Traffic Safety

Curbs are commonly used on roadways to serve for drainage managing, access controlling and other positive functions. However, curbs may also bring about unfavorable effects on drivers’ behavior and vehicles’ stability when hitting curbs, especially for high-speed roadways. In addition, numerous pavements have been experiencing wear off rapidly in recent decades, which significantly affected driving quality. However, previous study of pavement management factors as related to the happening and outcome of traffic-related crashes has been rare. The objective of this dissertation is to evaluate the influences of outside shoulder curbs, pavement management factors, and other tradition traffic engineering factors on the occurrence and outcome of traffic-related crashes. The Illinois Highway Safety Database from 2003 to 2007 and the Tennessee crash data from 2004 to 2009 was employed in this research. A few advantage statistics models were built to study the effects of curbs, pavement quality and other typical factors on both the occurrence and the outcome of crashes. These models include: the Zero-Inflated Negative Binomial models (ZINB), the Zero-Inflated Ordered Probit (ZIOP) model, the random effect Poisson and Negative Binomial model, as well as the Bayesian Ordered Probit (BOP) model. The findings of this study suggest that the employment of curbed outside shoulders on high-speed roadways would not pose any significantly harmful effect on the occurrence of crashes. On high-speed roadways with curbed outside shoulders in terms of the crash frequency, reducing speed limit from55 mphto45 mphwould not achieve any safety benefit. Crashes occurring on roadways with curbed outside shoulders are more likely to be no and minor injury related as compared to crashes on roadways without curbs. The increase of speed limit from 45 to 55 has relatively small effects on single vehicle crashes occurring on roadways with curbed outside shoulders. Rough pavements were associated with higher overall crash frequency but lower level of injury severity given that a two vehicle involved rear-end, head-on and angle crash has occurred. Pavements with more severe distress were related to lower crash frequency