Development of Crash Modification Factors and Benefit-cost Analysis of Lane Departure Crash Countermeasures PDF Download

Author: Irfan Uddin Ahmed
Publisher:
ISBN: 9780438384477
Category : Roads
Languages : en
Pages : 103

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Book Description
The World Health Organization (WHO) reports road traffic injuries are one of the leading causes of death worldwide with 1.2 million people dying in traffic crashes annually. Total losses in monetary value amounted to $836 billion in the US in 2010. According to the Federal Highway Administration (FHWA), the comprehensive cost of a single fatal crash is estimated to be $9.6 million (2016 dollars). There have been 37,461 fatalities in 2016 in the US, which was an increase of 5.5% from 2015. According to the Fatality Analysis of Reporting System (FARS), the traffic fatality rate for the US was 1.18 per 100 million vehicle miles traveled (MVMT) while Wyoming experienced 1.20 fatalities per 100 MVMT in 2016. The trend in recent crash rates reveals that Wyoming has always been facing higher fatality rates than the national average. Challenging roadway geometry, long driving distances, and adverse weather conditions could contribute to higher average crash rates in Wyoming. Research shows that a significant number of fatal and serious injury crashes result from lane departure crashes. Lane departure crashes include angle, head-on, sideswipe, and run-off-road crashes. Factors such as driver fatigue and drowsiness, distracted driving, poor road surface condition, adverse weather, challenging roadway geometry preventing easy passing maneuvers may result in increased lane departure crashes. Some of these contributing factors could be mitigated by providing countermeasures, such as centerline rumble strips, by adding passing lanes on a two-lane roadway, and by dividing the roadway into four-lane highways. This study analyzes and compares the safety effectiveness of these three countermeasures on a two-lane two-way highway in Wyoming. The roadway selected for this study is US 287 between Laramie and the Wyoming-Colorado Stateline. Statistical analyses and benefit-cost analyses were carried out to evaluate the safety effectiveness of the aforementioned countermeasures. Six years of crash data (2003-2008) were used to develop the Safety Performance Functions (SPFs) utilizing negative binomial and zero-inflated negative binomial (ZINB) regression models. A segmented dataset consisting of variable segment lengths was prepared using homogeneous roadway geometry and traffic volume data. SPFs were developed for total crashes, property damage only (PDO) crashes, fatal and injury (F+I) crashes as well as lane departure crashes. Numerous explanatory variables related to roadway geometry and traffic volume were considered in the modeling process. It was found that LOG(VMT), vertical grade, and presence of rumble strips were the significant variables in predicting crash frequency. AIC was used as the model selection criterion to find the best fit model. Observational before-after with Empirical Bayes (EB) method was utilized to develop Crash Modification Factors (CMF) to analyze the safety effectiveness of lane departure crash countermeasure. The results show that with the implementation of conversion to four-lane divided highway, there is an expected crash reduction of 52%, 55%, 86%, and 77% associated with total crashes, F+I crashes, PDO crashes, and lane departure crashes, respectively. Furthermore, the CMFs for centerline rumble strips indicate expected crash reduction of 69%, 52%, 89%, and 80% for total crashes, F+I crashes, PDO crashes, and lane departure crashes, respectively. The CMFs obtained for passing lanes show that an expected total crash reduction of 32%, F+I crash reduction of 20% and 25% crash reduction in lane departure crashes. The overall results from this analysis show that the highest percentage of crash reduction can be expected from the implementation of centerline rumble strips. All the CMFs indicated that all countermeasures are effective in reducing the frequency and severity of crashes. Finally, a benefit-cost analysis (BCA) was carried out using comprehensive crash costs calculated by following the Highway Safety Manual and the Wyoming Department of Transportation methods. The BCA provided the opportunity to determine which countermeasure provided the best return (benefits) on investment (project costs). It was found that the return on investment is the highest for the implementation of centerline rumble strips followed by addition of passing lanes. Conversion to four-lane divided highway resulted in the lowest benefit to cost ratio. One of the reasons for this could be the higher project costs of adding lanes and dividing the roadway than the other countermeasures investigated in this study. The safety analyses and the benefit-cost analyses carried out in this study show that the implementation of centerline rumble strips provides very high CMFs and benefit to cost ratio which may seem impractical. There could be a number of reasons for the overestimation of the CMFs and the benefits of centerline rumble strips.