Addressing the “Merge” Problem at Multilane Roundabouts

Phil Weber

Senior Project Manager
CIMA+

Phil Weber works at CIMA+ in Toronto, Ontario, and is a P.Eng. and P.E. with a Masters’ degree in transportation engineering. Over the past 20-plus years he has worked in the transportation field in both the public and private sectors. Disciplines have included transportation planning, traffic engineering, geometric design, human factors, and road safety. Phil is considered a national authority on roundabout planning and design in Canada, and has seen more than 100 roundabout designs through to construction to date.

This presentation builds on one presented in Green Bay in 2017 about the “merge”-type crash that can occur at multi-lane roundabouts. This is where a driver in the right lane enters beside traffic circulating in the inside lane and collides with a circulating driver exiting immediately downstream. Anecdotal evidence suggests the cause is some drivers thinking a through movement at a multi-lane roundabout is similar to a right turn at other intersections. This crash type is the leading reason why some multi-lane roundabouts are experiencing a much higher collision rate than expected. This paper will follow up on the two multi-lane roundabouts presented as case studies (the St. Joseph roundabout in the City of Ottawa, Canada, and the Homer Watson roundabout in the Region of Waterloo, Canada) to see whether high proportions of the merge-type crash on specific approaches continues to be experienced even after the installation of certain remedial measures. Then it will describe further comprehension testing carried out to evaluate two possible countermeasures developed based on the previous round of testing: a Yield sign plaque reading “Do Not Merge”, and a Yield sign plaque depicting the message “Yield to Both Lanes”. A series of test slides were created to depict the countermeasures, plus the instance of no countermeasure, and members of the public were asked to respond “yes” or “no” to the same question for each: is it okay to enter the roundabout? The test slides were presented in random order and results statistically compared to determine whether either countermeasure improved understanding that you should not enter a roundabout beside circulating traffic.

This presentation is about learning the root causes of the merge-type conflict and strategies to counter them. Fundamentally the issue is one of driver perception about whether a roundabout should be considered one intersection or a series of T-intersections. The target audience is roundabout designers, and public agency staff responsible for monitoring roundabout operations and providing roundabout public outreach.

Similar research is being undertaken by the FHWA, but is expected to take a number of years to complete. It is hoped this presentation can complement the research. It may result in a new sign plaque that can be installed at problematic locations, or provide insight on what efforts can be taken to educate the public on how to avoid the merge-type conflict at multi-lane roundabouts.