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Roundabouts

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Because of their superiority in certain situations, modern roundabouts (not be confused with traffic circles) became popular around the world. Currently over 2,300 roundabouts are in use in North America; with almost 300 new ones build each year. Some states even regulate that every new signal must be analyzed to see if roundabouts are not a better option for traffic control.

Michigan has also recognized the benefits of roundabouts. There are many throughout the state from the first mini roundabout in Dimondale to large three-lane roundabouts in Oakland County. 

The Michigan Department of Transportation (MDOT) has recently completed installations of roundabouts on some freeway interchanges, and urban arteries. This includes the Lee Road / US-23 interchange as well as M-53 and 26 Mile Road. The most recent freeway interchange converted from signals to roundabouts in our area was the Geddes Road interchange on US-23. 

The City of Ann Arbor built its first modern roundabout at the intersection of Huron Parkway and Nixon Road in June of 2009. This intersection was under All Way Stop control, but was failing from capacity and safety points of view. In the process of upgrading the intersection, the city performed a roundabout analysis, which showed that a small roundabout would reduce vehicular and pedestrian delays better than a signal might. In addition, queues that were forming on Nixon in the morning and evening rush hours would be much shorter with the roundabout, but longer with a signal. The other issue resolved by a roundabout is the difficulty of coordinating a signal at this intersection with two Plymouth Road signals nearby. Finally, a roundabout would improve safety, as lower speeds in general reduce the number but most importantly the severity of crashes. As a bonus there is much lower maintenance requirement compared to the signal, and fail safe operation under power outages. ​

In October, 2010 the City of Ann Arbor, in partnership with MDOT, opened the Earhart / Geddes roundabout. The replacement of the existing signal at this intersection with the roundabout significantly improved operation of the whole system. Roundabouts work poorly with platooned traffic that is released by signals, and vice versa, signals work poorly when they receive a random pattern of traffic. Therefore, systems containing signals and roundabouts are not compatible and that was one of the reasons the city decided to replace Earhart / Geddes signal with the small, single lane roundabout. An additional benefit of this project was a big improvement to the non-motorized system by filling sidewalk gaps on Earhart and adding a non-motorized path on Geddes with a separate bridge over US-23.

The Washtenaw County Road Commission​ converted several​ intersections to roundabouts. There is one important difference in the area describing how to navigate the modern roundabout. Ann Arbor law requires that vehicles stop for pedestrians approaching the crosswalk. This is not covered in WCRC documents as they are not based on City of Ann Arbor regulations. In Ann Arbor drivers must​ stop for pedestrians in the crosswalk and yield to traffic in the circle. This is a very important difference to keep in mind.​