September 13


Intersection Spacing – Roundabout/Dual Left Lane Integration

By Mike Spack

September 13, 2011

Orem Utah Roundabouts

Landform is working on an updated master plan for The Cor (a large mixed use/neo-traditional development in Ramsey, MN that has struggled due to the economic downturn).  They brought me in to update some traffic forecasts which Mark Lenters (Ourston Roundabout Engineering) can use to redesign a key intersection in the development. 

How close can an intersection controlled with a roundabout be to another intersection?  Based on operational experience around the country, much closer than if the intersection was controlled with a traffic signal – often a couple hundred feet is all the spacing that's needed.  This is pretty well established and why Mark was brought in for this project, but how close can a roundabout controlled intersection be to a traffic signal controlled intersection that has dual left turn lanes at it?

I raised this question to Mark early in the project and he's been kind enough to share the real world example (below) at Utah Valley University in Orem, Utah.  There's only 200 feet between the roundabout and University Parkway.  I haven't found any references to how well this area operates, but it's a creative example of putting a roundabout close to a large intersection.

Roundabout-dual lefts

  • There is a roundabout near me that is within the queue length of adjacent signals, even though it is quite far from one of them. One leg of the roundabout is the back entrance to a regional shopping mall. It’s definitely suboptimal.

  • being a traffic engineer in the utah area, it does operate pretty well during most the day. However, the southbound traffic does back up into the roundabout during peak times at the university and northbound traffic experiences some friction with traffic maneuvering to turn right or left at the roundabout with such a short distance. as would be expected, the traffic that backs into the roundabout inhibits other movements and can create a “locking” effect. for this particular location, i think there are better solutions to address the particularly heavy movements that would improve some of the issues i noted.
    there is another one in front of the university of utah, closely adjacent to a major roadway, and this one uniquely has a light rail line running through the middle of it. It seems to do ok most the day with the similarly noted backing into the roundabout during peak hours.

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    Mike Spack

    My mission is to help traffic engineers, transportation planners, and other transportation professionals improve our world.

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