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Roundabouts In St. Louis

A roundabout is basically a large circle in the middle of an intersection. A roundabout replaces a traffic signal. Vehicles move in a counter-clockwise direction through the intersection and all entering traffic yields to the traffic already in the circle. If there is no traffic in the circle you do not have to stop, therefore reducing your delay time. Accidents are generally decreased because conflict points are minimized (i.e. no left turns) and speed is lower compared to signalized intersections. Roundabouts also handle a greater volume of traffic than a conventional signalized intersection.

MoDOT constructed St. Louis's first roundabout at Route 141 and Woods Mill Road in 2002. Click here to view a graphic of the Rte. 141 and Woods Mill Rd. roundabout.

MoDOT has a two-lane roundabout at Route 109 and Route 100, as well as at Round 109 and Pond Grover Loop in Wildwood.  Here's information on using a two-lane roundabout.

Roundabout sketch

Roundabout Quick Facts

  • Entering traffic yields to circulating traffic.

  • Circulating traffic always keeps moving.

  • Roundabouts work well with very heavy traffic.

  • Slows traffic on fast roads, reducing accidents.

Latest study by the Insurance Institute For Highway Safety:
  • Accidents reduced by 39 percent;

  • Collisions resulting in injuries dropped by 76 percent;

  • Crashes involving fatal or incapacitating injuries fell by 90 percent;

  • Traffic delays cut by as much as 75 percent;

  • Save up to $5,000 a year vs. traffic signals.

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