Date of Award


Degree Name

Master of Science in Engineering


Civil and Construction Engineering

First Advisor

Dr. Valerian Kwigizile

Second Advisor

Dr. Osama Abudayyeh

Third Advisor

Dr. Hexu Liu


Roundabouts, traffic signals, delays, unbalanced flow, VISSIM

Access Setting

Masters Thesis-Open Access


A roundabout is a circular intersection where drivers travel counterclockwise around a center island in the United States. Roundabouts can be more beneficial than the conventional intersections because they increase the capacity of the intersection and reduce delays and crashes at the intersection. However, the performance of roundabouts can be severely affected by unbalanced traffic flows among the approaches. While the resulting delays can be mitigated by installing traffic signals, there is a lack of clear criteria on when to install a traffic signal at a roundabout. This research focuses on establishing criteria for installing traffic signals at two-lane roundabouts using delay as the measure of the effectiveness of the performance. These criteria are applicable to two-lane roundabouts with unbalanced flow between the legs of the roundabout and when adding lanes is not an option.

The analysis was carried out using VISSIM 9.0 by creating a microscopic simulation model according to the study area geometric features and traffic inputs. Five different cases were considered to quantify the impact of geometric features and traffic inputs on the delay at a roundabout. Criteria for installing a traffic signal were established and are presented in this report.