Josh Saak
Traffic Design Engineer

Roundabouts are one option used for traffic control at an intersection. The Ada County Highway District has constructed several roundabouts and more are proposed or being evaluated at various intersections around the county.

Benefits of Roundabouts

  • Improve safety
  • Provide better traffic flow and reduced delay
  • Fewer vehicle conflict points than a traditional intersection
  • Business and community enhancement
  • Decrease air pollution - emissions are reduced by avoiding frequent starts and stops

Click on the image at the right to view the features of a basic roundabout.

Roundabouts and safety

Roundabouts typically eliminate the most severe intersection accidents — T-bones and head-on collisions. They have fewer vehicle conflict points than a traditional intersection which results in 48% less accidents than signalized intersections and 78% less injury and fatal crashes than signalized intersections.*


How to use a roundabout

Read below to learn more about using a roundabout as a motorist, bicyclist, or pedestrian.

  • Slow down
  • Enter appropriate lane if there are multiple lanes.
  • Yield to pedestrians in the crosswalk.
  • Yield to motorists already in the roundabout, then merge into traffic flow when it is safe.
  • Stay in your lane - never change lanes or pass in the roundabout.
  • Do not stop or pass in a roundabout.
  • Signal your turn and yield to pedestrians in the crosswalk when exiting the roundabout.
Cyclists can either ride with traffic inside the roundabout or circulate as a pedestrian, using the sidewalk. Always yield to pedestrians.

Riding with traffic:

  • Assert position and take center of the lane as you approach.
  • Follow the same rules as vehicles and yield as you enter the roundabout.

Circulating as a pedestrian:

  • Most roundabouts have special ramps that lead to sidewalks.
  • Dismount and walk your bike when using crosswalks.
  • Cross only at crosswalks and always stay on the designated walkways.
  • Pedestrian islands may allow you to cross one section at a time.
  • Watch for cars entering and leaving the roundabout. You have the right-of-way, but proceed carefully.
  • Your best protection is awareness.
  • Never cross to the center island.


If an emergency vehicle approaches, exit the roundabout immediately and then pull over. Do not stop in the roundabout.

Large vehicles and roundabouts

Roundabouts are designed to accommodate large trucks, farm equipment and emergency vehicles. The 'truck apron' is specifically designed so these types of vehicles can drive over it and make their way safely through the intersection. Watch the video below to learn more (video courtesy of the Federal Highway Administration, Modern Roundabouts: A Safer Choice).

ACHD and roundabouts

  • Click here to learn more about ACHD's Countywide Roundabout Preservation Plan

  • Learn how the new roundabout at 36th, Hill, and Catalpa will work by watching the video.

More information

Learn more about roundabouts at these web sites:

* Statistics from the National Cooperative Highway Research Program (NCHRP), Report 672