Abstract Manager

Canadian agencies have adopted roundabouts as alternative treatments to signalized intersections. Generally, they improve safety by reducing total conflict points, lowering speeds, and reducing collision severity. Multilane roundabouts have also grown in popularity for busier intersections as substitutions for signal upgrades. However, multilane roundabouts experience higher collision frequencies than single-lane roundabouts due to the increased number of conflict points.

Turbo-roundabouts are newer, revised versions of multilane roundabouts. They originate in The Netherlands and have been adopted in other European countries. Their main benefits are reducing conflict points (compared to their multilane counterparts), promoting lower speeds, and discouraging lane changing. International research also indicates that their capacities are similar to other multilane roundabout treatments.

As a result, as part of ongoing development within the Town of Canmore, Alberta, a five-legged turbo-roundabout was proposed, designed, and constructed. This presentation serves as a unique opportunity to evaluate turbo-roundabout performance within a Canadian context and includes:

• Turbo Roundabout Features and Benefits – The main geometric features that define what a turbo-roundabout is, and how these serve as benefits. Turbo-roundabouts are characterized by two spiral, circulatory lanes that start as the inner circulating lane and transition to the outer lane, before ending. Lane dividers prevent lane changing and promote lane selection before entering the roundabout. Further, turbo-roundabout approaches are generally at 90o entries, as opposed to 30km/h deflections.
   
• Designing for Canadian Contexts – Currently, there are no guidelines for Canadian turbo-roundabouts. Their design requires reliance on guidance from outside jurisdictions. Lane dividers are one key feature of turbo-roundabouts. Research into alternative lane divider treatment was conducted to find designs that are suitable for winter conditions and heavy truck traffic, allowing truck tires to overtrack along lane dividers. A summary of the different options and designs that were considered is provided.
   
• Operational Summary – There is a limited understanding of the operational impacts and requirements for turbo-roundabouts in North American contexts. Post-construction traffic operations studies were conducted to summarize operational characteristics, including critical gaps, follow-up headways, and driver behaviors within turbo-roundabouts to help better understand their capacities in Canadian settings.

This presentation summarizes the features, benefits, and lessons learned designing for turbo-roundabouts in Canada. Presentation topics also include our research conducted to summarize the turbo-roundabout traffic operations and our findings. Recommendations for future research, work, and opportunities are also discussed.