Master of Science / Department of Civil Engineering / Sunanda Dissanayake / Construction of by-pass lanes at rural intersections typically has been considered a low-cost safety improvement. Safety analysis utilizes two common approaches to evaluate treatment effectiveness: before-and-after study and cross-sectional study. This research performed paired sample t-test statistical analysis to estimate changes in total of crash frequency, crash rates, EPDO crash frequency, and EPDO crash rates at intersections, three to five years after adding a by-pass lane compared to identical time period before the by-pass lane was added. Crash data between 1990 and 2011 were obtained from Kansas Crash and Analysis Record System (KCARS) maintained by the Kansas Department of Transportation (KDOT). In order to perform a cross-sectional study, intersections with by-pass lanes were compared to intersections with no countermeasures; crash data were obtained for more than 1,100 intersections in the state of Kansas. According to before-and-after study, addition of by-pass lanes improves safety at unsignalized rural intersections; crashes and their severities are reduced after adding by-pass lanes. But, these reductions are not statistically significant under 95% confidence level. However, when considering intersection related crashes, a statistically significant reduction in crash rates is happened after adding by-pass lanes at 3-legged intersections. In cross-sectional study, crashes and their severities are lower at 3-legged intersections with the by-pass lanes versus 3-legged intersections without the by-pass lanes. However, these reductions are not statistically significant under 95% confidence level. When considering 300 feet intersection crash box, statistically significant reductions are happened at 4-legged intersection. In contrast, crashes and their severities increased at 4-legged intersections with the by-pass lanes, but these changes are not statistically significant under 95% confidence level. The Crash Modification Factors were calculated to evaluate safety effectiveness of adding by-pass lanes at unsignalized rural intersections. The calculated CMFs less than 1.0, indicate a reduction in crashes after implementation of by-pass lanes. Finally, this study concluded that expected crashes at intersections with by-pass lanes are lower than intersections without by-pass lanes.

Major safety concerns are present at rural high speed intersections. When long uninterrupted tangents are located near rural intersections, the drivers can become inattentive to upcoming decision points. Traffic control devices could aid in mitigating these occurrences by warning drivers of upcoming decision points. One such device is transverse rumble strips, which act to provide motorists with an audible and tactile warning that their vehicle is approaching a decision point of critical importance to safety. The objective of this research was to determine if the presence of transverse rumble strips were an effective warning device for drivers approaching rural stop-controlled intersections. To evaluate the effectiveness of transverse rumble strips, vehicle speeds were measured at three locations along the approach to an intersection both before and after the installation of rumble strips. Vehicle speeds were measured at nine rural stop-controlled intersection sites in Texas. Overall, the installation of rumble strips generally produced small, but statistically significant (p ? 0.05), reductions in traffic speeds. There were some negative driver behavioral impacts (i.e., speed increases) that occurred after the installation of rumble strips. There were a few instances where speed change reductions of greater than 1 mph occurred, however, the overall trend was that speed change reductions were equal to or less than 1 mph. Although the rumble strips did not produce meaningful reductions in traffic speeds, they should still be considered based upon previous accident reductions and minimal installation costs.

Major safety concerns are present at rural high speed intersections. When long uninterrupted tangents are located near rural intersections, the drivers can become inattentive to upcoming decision points. Traffic control devices could aid in mitigating these occurrences by warning drivers of upcoming decision points. One such device is transverse rumble strips, which act to provide motorists with an audible and tactile warning that their vehicle is approaching a decision point of critical importance to safety. The objective of this research was to determine if the presence of transverse rumble strips were an effective warning device for drivers approaching rural stop-controlled intersections. To evaluate the effectiveness of transverse rumble strips, vehicle speeds were measured at three locations along the approach to an intersection both before and after the installation of rumble strips. Vehicle speeds were measured at nine rural stop-controlled intersection sites in Texas. Overall, the installation of rumble strips generally produced small, but statistically significant (p ? 0.05), reductions in traffic speeds. There were some negative driver behavioral impacts (i.e., speed increases) that occurred after the installation of rumble strips. There were a few instances where speed change reductions of greater than 1 mph occurred, however, the overall trend was that speed change reductions were equal to or less than 1 mph. Although the rumble strips did not produce meaningful reductions in traffic speeds, they should still be considered based upon previous accident reductions and minimal installation costs.

Safety at intersections is of significant interest to transportation professionals due to the large number of possible conflicts that occur at those locations. In particular, rural intersections have been recognized as one of the most hazardous locations on roads. However, most models of crash frequency at rural intersections, and road segments in general, do not differentiate between crash type (such as angle, rear-end or sideswipe) and injury severity (such as fatal injury, non-fatal injury, possible injury or property damage only). Thus, there is a need to be able to identify the differential impacts of intersection-specific and other variables on crash types and severity levels. This thesis builds upon the work of Bhat et al., (2013b) to formulate and apply a novel approach for the joint modeling of crash frequency and combinations of crash type and injury severity. The proposed framework explicitly links a count data model (to model crash frequency) with a discrete choice model (to model combinations of crash type and injury severity), and uses a multinomial probit kernel for the discrete choice model and introduces unobserved heterogeneity in both the crash frequency model and the discrete choice model, while also accommodates excess of zeros. The results show that the type of traffic control and the number of entering roads are the most important determinants of crash counts and crash type/injury severity, and the results from our analysis underscore the value of our proposed model for data fit purposes as well as to accurately estimate variable effects. / text