Roundabouts

Benefits of Roundabouts

The City of Shoreline’s redesign of the 145th Street and I-5 interchange is based on data that shows the benefits of roundabouts for safety, traffic flow, efficiency, and cost. According to WSDOT traffic studies, roundabout intersections can provide lasting benefits in many ways, including:

Roundabouts reduce the rate and severity of collisions.

Roundabouts reduce the likelihood of collisions by 37%, injury crashes by 75%, fatality collisions by 90%, and pedestrian–car collisions by 40%. Roundabouts also significantly reduce the likelihood of T-bone and head-on collisions.

Roundabouts calm traffic.

Roundabout speeds are usually about 20 mph. Drivers must slow down and yield before entering the roundabout and they are less likely to feel the need to speed up to try to “beat the light.”

Roundabouts are more efficient.

Roundabouts improve traffic flow and reduce waiting time. They facilitate a continuous flow of traffic and can accommodate higher traffic volumes with fewer lanes on the approaching streets.

Roundabouts are cost-effective.

Long-term costs for roundabouts are lower because traffic signal maintenance and electrical costs are not needed. Roundabouts are also more effective during power outages. The cost of building a roundabout is comparable to that of a signal-controlled intersection.

Roundabouts accommodate all sizes of vehicles.

Large trucks, buses, and oversize vehicles can straddle both lanes when driving in a roundabout. Most roundabouts have a truck apron, a raised section of pavement near the center of the roundabout that gives large vehicles extra room to navigate the roundabout.

Roundabouts are safer for pedestrians and bicyclists.

Crosswalks are set back from the intersection, allowing drivers more time to react to pedestrians. Roundabout islands also provide refuge for crossing pedestrians and bicyclists.

Click on the “+” symbols for more information.


How to Navigate Multilane Roundabouts

  • Check the signs to choose the correct lane for your destination
  • Yield to traffic already in the roundabout (all lanes)
  • Stay in your lane through the roundabout
  • Give buses and large vehicles space when approaching and traveling through the roundabout, as they may take more than one lane
  • Yield to people in crosswalks

For more information, please visit the City of Shoreline’s Roundabouts webpage.