Date of Award


Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)


Civil Engineering


Per E. Gårder

Second Committee Member

Thomas C. Sandford

Third Committee Member

Jonathan D. Rubin


Many drivers are apprehensive to accept a roundabout as a viable form of intersection, but their safety and mobility benefits are increasing their popularity among designers. This thesis is an in-depth study of a specific approach at a roundabout in Bangor, Maine. The location was previously two separate "T" intersections, one of which was a high crash location. The reduction in reported crashes at this location after installation of the roundabout warrants a performance evaluation that not only looks at all the drivers using the intersection as a whole, but also focuses on different groups of users to determine, if there is a problem, where it may lie within the population. The performance evaluation conducted in this thesis began by looking at the critical gap value for a specific approach to the roundabout, a value at which 50% of the users would accept a gap in the conflicting traffic stream. This was done for the following groups: Drivers aged <20, 20-29, 30-39, 40-49, 50-59, 60-69, 70+, males only, females only, and whether or not a cell phone was in use while negotiating the merge into the circulating flow. These critical gap times were then used to calculate an average delay that drivers utilizing the roundabout experience, which was in turn used to determine the level of service for that approach. It was found that the <20, 70+, and cell phone groups had a higher critical gap value, leading (through delay equations) to a lower level of service. However, these findings are not validated because not enough data was collected within each of these groups. The reason for this is the location of the roundabout, which is in a somewhat industrial area that does not see many drivers that are on the extreme ends of the data spectrum and the number of drivers using a cell phone were a small proportion of all the drivers observed. In total, 2,366 observations were made with only 26 being under the age of 20, 64 being 70 years old or older, and 162 using a cell phone. The average actual delay times experienced by drivers was also measured and compared to three methods for estimating delay to evaluate the accuracy of the estimation methods. Two of the three methods are new equations offered by the 2010 edition of the Highway Capacity Manual (HCM 2010). It was found that the HCM 2010 overestimates the delay times, which has the potential to give an engineer or city planner the incorrect impression that a roundabout is not a viable option when it may very well be. As an aside, the drivers using cell phones were categorized into the aforementioned groups to see which groups used cell phones the most while negotiating the roundabout. It was discovered that females used cell phones more than men at this intersection.