Ada County Highway District

Traffic Roundabouts Improving Safety and Traffic Flow

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 fewer crashes than signalized intersections and fewer injury and fatal crashes than signalized intersections. Additional benefits are:

  • Improve safety when compared to signalized intersections
  • Better traffic flow and reduced delay when compared to more conventional intersections
  • Fewer vehicle conflict points than a traditional intersection
  • Business and community enhancement – opportunities for unique “branding” or landscaping in the center island
  • Decrease air pollution – reduced emissions by avoiding frequent starts and stops
Image of 36th St Hill Rd Catalpa dogbone

How to Use Roundabouts Mortorists, Bicyclists and Pedestrians

Illustration of roundabout features in png
Illustration of roundabout signs in png
Illustration of roundabout signs in png


As a motorist, to travel into a roundabout remember to:

  • Slow Down.
  • Yield to pedestrians in the crosswalk.
  • Yield to motorists already in the roundabout, then merge into traffic flow when it is safe.
  • Enter appropriate lane if there are multiple lanes.
  • Stay in your lane. Do not change lanes or pass in the roundabout.
  • Signal your turn and yield to pedestrians in the crosswalk when exiting the roundabout.
  • If an emergency vehicle approaches, exit the roundabout immediately and pull over. Do not stop in the roundabout.
  • How do multi-lane roundabouts work?
    View this video from our neighbors to the north in Canada.


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

Circulating as a pedestrian

  • Many roundabouts have special ramps prior to entering the circulating roadway that lead to sidewalks.
  • Dismount and walk your bike when using crosswalks.


As a pedestrian, you have the right-of-way, but always proceed carefully.

  • 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. Be aware and proceed carefully.
  • Your best protection is awareness.
  • Never cross to the center island.

For additional information:

ACHD Main Line: 208-387-6100
Traffic Engineering:  208-387-6140
Or contact us at: Tell Us

We Drive Quality Transportation For All Ada County ~

Ada County Highway District © 2017
For Questions or problems with this Web site contact the Webmaster
Privacy Policy