Estimating the effect of geometric features of side traffic barriers on crash severity of interstate roads in Wyoming.

Past roadside safety studies mostly evaluated the impact of traffic barrier geometric features using simulation tools or by conducting field crash tests. While past simulation and field crash tests could present important findings for upgrading the geometric design of traffic barriers, there is still a gap regarding conducting an actual data analysis on side traffic barriers crashes with regards to their geometric dimensions. This paper aims at filling this gap by combining a statewide dataset of side traffic barrier geometric features with historical crashes on interstate roads in Wyoming. Therefore, geometric features including system height, post-spacing, lateral offset (from the edge of pavement), and side-slope of over 150 miles of side traffic barriers were inventoried by conducting a field survey on interstate roads in Wyoming. For the statistical analysis, a random-parameters ordered logit model was utilized to investigate variables impacting crash severity of side traffic barriers. It was found that system height could significantly impact the crash severity of side box beam barriers. Box beam barriers with a system height between 25 and 31 in. were identified to be less severe in comparison to other height categories, while showing minimum risks of severe crashes in the system height of 29-31 in.. On the other hand, box beam barriers with a height taller than 31 in. may increase crash severity.

Safety analysis of the new synchronized and milwaukee B interchanges in comparison to existing designs.

Interchanges have high crash rates and large impacts on traffic operations. The main objective of this research is to analyze the safety performance of two new interchanges, the synchronized interchange and the Milwaukee B interchange. The primary method of study was microscopic simulation modeling using the Surrogate Safety Assessment Model (SSAM) program to estimate the quantity and type of conflicting interactions in each interchange. A comprehensive series of simulation scenarios were considered to include different conditions of traffic volumes, traffic turning ratios, traffic distribution, and heavy vehicles percentages. Afterward, outcomes were analyzed with two-way Analyses of Variance (ANOVAs) to compare the mean values of conflicts. Based on the results, the diverging diamond interchange (DDI) and Milwaukee B were the safest designs regarding observed conflicting interactions in the simulation models; however, the DDI did not seem as reliable from the viewpoint of wrong way movements. The new synchronized interchange, the parclo B, and the Milwaukee A (an existing interchange in Milwaukee, WI) showed the same rate of conflicts. The synchronized interchange may be advantageous because it was estimated to reduce the severity of crashes due to fewer crossing conflicts, a lower speed of conflicts, and a higher time to collision. The conventional diamond was the most dangerous design based on our measures. The DDI and the synchronized interchange look like plausible substitutes for reconstructing an unsafe diamond interchange due to the similarities in their required space.