Olsson Associates

Articles

Roundabouts: Knowing when to use

Monday, January 13, 2014

Andrew Meyerkord, PE, Transportation

For some, roundabouts invoke anxiety-producing images of driving trapped in an endless circle with no easy exit. However, roundabouts can be a simple way to avoid being stuck at a red light at an empty intersection, wondering why you have to wait for the light to turn green when no other cars are visible for miles. Are roundabouts good or bad in your mind? The bottom line is that well-designed roundabouts are a legitimate tool for traffic management, when used in the appropriate context.

In general, if roundabouts are designed well, they provide speed control at all times of day. Benefits of roundabouts and speed control include the following:

  • Eliminating conflicts associated with left-hand turns and right-angle turns
  • Increasing the likelihood of drivers yielding to pedestrians
  • Making crashes less frequent and less severe
  • Lowering car emissions
  • Lowering intersection operating and maintenance costs
  • Increasing intersection functionality by about 15 years when compared to  signalized intersections

Single-lane roundabouts designed for low speeds are one of the safest tools for intersection management. Drivers have no lane decisions to make, pedestrians cross one lane of traffic at a time, and bicycles and cars can flow safely. For example, Olsson designed two single-lane roundabouts for the main intersections in a mixed-use development that included a hospital, townhomes, and light commercial. The development was also interconnected with a multiuse trail.

Multilane roundabouts increase the number of conflicts and driver decisions, but a well-designed, multilane roundabout still has an overall safety performance that is better than signalized intersections in a comparable traffic environment, especially in terms of fatal and injury crashes. Olsson has completed designs for many different multilane roundabout configurations for various situations, including interchanges, closely spaced intersections, and those to help improve access management along developed corridors.

Despite the benefits of roundabouts, they have their downsides. Roundabouts are usually not a good choice for intersections that have a mix of high- and low-volume streets. Roundabouts treat all movements equally, causing delays along the high-volume streets. Roundabouts are also not appropriate along emergency routes, and they tend to need more space at the intersection site than a standard, signalized intersection.

Roundabouts can be a valuable tool for municipalities and private developers, but it is important to choose them for the appropriate traffic situations. The roundabouts must be designed well to fully achieve their many benefits.

Olsson’s Transportation engineers have a depth of experience designing roundabouts to solve a variety of traffic challenges. Feel free to call the Transportation team at 402.474.6311 if you have questions about choosing the best traffic tools for a challenging issue in your community.

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