Freeway Truck Traffic Safety in Wyoming: Crash Characteristics and Prediction Models

Abstract

The State of Wyoming experiences a high percentage of truck traffic along all its highways, especially Interstate 80 (I-80). The increased interactions between trucks and other vehicles have raised many operational and safety concerns. This paper presents a safety analysis and a development of safety performance functions (SPFs) along I-80, with a focus on truck crashes. Nine years of historical crash data in Wyoming (2008–2016) were used to observe the involvement of light, medium, and heavy trucks in crashes. Analysis of the major contributory factors showed that 54% of the total truck-related crashes occurred during icy road conditions and about 46% during snowy weather conditions, and approximately 45% involved driving too fast and driving in improper lane. The analysis also included segments with horizontal curves and vertical grades and their impacts on truck crashes. The crash rate analysis showed higher truck crash rate compared with total crash rate considering equal vehicle miles traveled as exposure. A zero-inflated negative binomial model was applied to develop Wyoming-specific SPFs for various truck crash types. The effects of traffic, road geometry characteristics, and weather parameters influencing different truck-related crashes were quantified from these models. Downgrades and steep upgrade sections were found to increase truck-related crashes. The number of rainy days per year was found to be a significant variable affecting truck-related crashes. On the other hand, the presence of climbing lanes has significant safety benefits.

Accident prediction modelling for expressways: a review

“…Wen et al [56] found that the curvature was positively associated with the property damage accidents only. Haq et al [31] found a decreasing impact of horizontal curve radius on the truck related accidents. Studies also show that setting more gradual horizontal curves can reduce the number of accidents [46].…”

“…Traffic composition was used as an important independent variable by various researchers to identify the safety effects on expressway. Some researchers [20,24,31] found that higher percentage of trucks in traffic volume on expressway causes more number of accidents, and this could be attributed to the difference of speed between light vehicles and heavy vehicles. However, other researchers [11,47,57] found that high fraction of trucks and trailers in traffic volume result in decreasing accident risk.…”

“…This is a contradictory conclusion as compared with the previous investigations [18,37,39,48,56] and need to be further investigated. Downgrade sections of expressway found more unsafe as compared to upgrade sections and this could be attributed to the failure of brakes of heavy vehicles due to frequent application to control speed [7,24,31,37,58]. Increase in vertical grade found more injury accidents on expressway, and this could be attributed to adverse impact on stopping sight distance on steep grades [ 2 7 , 5 6 ] .…”

“…Lane width less than 3.25 m and more than 3.75 m were considered as undersized and IOP Publishing doi:10.1088/1757-899X/1236/1/012011 7 oversized segments respectively [55]. Some researchers found a decreasing impact of adding the climbing lane on the accident frequency [24,31,37] along section with steep grades. This could be attributed to the reduction in interaction among light vehicles and heavy vehicles after adding climbing lane.…”

“…Haq et al [31] applied a zero inflated negative binomial (ZINB) model for the expressway in the state of Wyoming to develop APMs for truck accidents. The ZINB model is good for over-dispersed accident frequency data that have excess zeros and offers enhanced goodness-of-fit than the NB model [32].…”