According to Federal Motor Carrier Safety Administration (FMCSA), truck involvement in fatal crashes is more on rural areas than on urban areas. The Fatality Analysis Reporting System (FARS) encyclopedia also indicates that truck involvement in fatal crashes are approximately 12% of the total fatal crashes in the nation and 14 % in The State of Ohio. One area for potential concern is the role of vertical curves on truck crashes. In the design of vertical curves stopping distance, grade and length of the curve are important factors taken into consideration. Vehicle operations on vertical curves are influenced by the grade of the curve, stopping sight distance and vehicle speed. These factors may create operational issues for vehicles traveling on vertical curves and in turn increase the likelihood for crashes. Truck specific studies in the past have focused on geometric roadway factors associated with crashes on vertical curves. Most of the research studies are focused on crest curve truck crashes, and little research has been done on crashes on vertical sag curves.
The main research goal of the study is to develop prediction models to evaluate the impact of geometry, traffic volumes and speed on truck-related crashes on two-lane rural vertical curves. The accomplishment of the research goal is achieved by setting five objectives. The first objective is to develop three crash prediction models using negative binomial regression model. These models are 1. Full model - for all vertical curves 2. Reduced model I - for crest curves only and 3. Reduced model II - for sag curves only. The dataset includes 1,935 vertical curve segments with 205 truck crashes from 2002-2006. In second and third objective, Full Bayes approach is used to enhance the results obtained in the Reduced Models I and II. These results are then compared to the initial models. The fourth objective is evaluating the vertical curve variables which are statistically significant with truck-related crashes. These results show that higher grade change for the length of the vertical curve, total width in the range of 24 to 26ft, more number of passenger cars and trucks, increases the truck-related crashes on both crest and sag curves. Low speed limit on crest curves and high speed limit on sag curves increases truck-related crashes which may seem counter intuitive. The fifth objective is to provide suggestions on effective methods to reduce truck related crashes and improve safety. Some potential areas for design improvement may include flattening of steep vertical curves, advisory speed signs and increasing the roadway width on rural vertical curves in Ohio.