Available at: https://digitalcommons.calpoly.edu/theses/2950
Date of Award
12-2024
Degree Name
MS in Civil and Environmental Engineering
Department/Program
Civil and Environmental Engineering
College
College of Engineering
Advisor
Anurag Pande
Advisor Department
Civil and Environmental Engineering
Advisor College
College of Engineering
Abstract
Turbo roundabouts are multilane roundabouts that utilize a spiral design with raised lane dividers to guide traffic flow effectively. While they have seen widespread use in Europe, California is the second state in the US (after Florida) to have installed a turbo roundabout. Turbo roundabouts separate the ingress and circulating lanes. The concept was first proposed and implemented in the Netherlands to address safety concerns and improve traffic flow efficiency on conventional multilane roundabouts.
This research evaluates the first-ever turbo roundabout in California and compares its safety and operational performance with the previously existing 4-legged signalized intersection. The research team obtained safety and operational performance measures using well-calibrated simulation models and video analytics of real-world conditions recorded before and after the installation of the turbo roundabout. The safety metrics include surrogate safety measures defining traffic conflicts between vehicles, enabling a more prompt safety evaluation compared to multi-year collision data. The results show that the turbo roundabout effectively reduced crash potential and queuing delays at this site. The real-world conflict data show that more severe crossing and head-on conflicts at the former 4-legged signalized intersection have all but been eliminated.
The rear-end conflicts that do occur on the roundabout involve vehicles traveling at significantly reduced speeds compared to similar conflicts observed at the signalized intersection. The results show that turbo roundabouts may be an effective option on rural routes where the siting criteria for multilane roundabouts are satisfied. Given the timeline for this research project, the evaluation was conducted within months of the roundabout’s completion. It is therefore advised that California Department of Transportation (Caltrans) continues to monitor traffic crash data to ensure that the long-term crash data shows the expected safety improvement.