Roundabouts WORK

I’m making this post to share some info related to the positive impacts of roundabouts on traffic congestion. I’ve always heard that they helped, but wanted to be able to point to specific studies and credible sources that backed that up.

***I am aware that roundabouts do impact communities in different ways… this is just about traffic congestion (and safety).***

Some specific areas in Washington that I’ve frequently driven through that either are currently building roundabouts or have concrete plans under way to do so include the west side of Hood Canal Bridge (Hwy 104) and Sultan (Hwy 2 – Old Owen Rd/ Red Apple Market).

As many have probably experienced, trying to turn east onto Hwy 104 from Port Townsend or Port Ludlow was dangerous and often involved a lot of waiting. So far the new roundabouts along Hwy 104 have helped in my experience.

Likewise, everyone in the Seattle area is probably aware of the traffic nightmare that is returning home westbound along Hwy 2 passing through Startup and Sultan, where one or two lights cause 2+ hour delays every Sunday. The addition of a roundabout has been funded for this route, and will likely be completed in 2026.

Generally, roundabouts have been found to be safer for cars and pedestrians, better for traffic flow, and better for the environment.

Anyway, here are some links that back this up:

• General traffic flow benefits (and other benefits):
  • https://www.iihs.org/research-areas/roundabouts#traffic-flow-benefits (a number of studies linked on this page)
  • https://wsdot.wa.gov/travel/traffic-safety-methods/roundabouts
• Studies involving Washington:
  • https://www.iihs.org/research-areas/bibliography/ref/1844
    • Quote: “…Average intersection delays during peak hours at the three sites were reduced by 83-93 percent. Traffic congestion, as measured by the vehicle-to-capacity ratio, was reduced by 58-84 percent.”
  • https://www.iihs.org/research-areas/bibliography/ref/2033 (Bellingham)
    • Quote: “…Driver support for the roundabouts increased from 34% before construction to 70% one year after.”
    • Quote: “…findings generally are consistent with prior research finding substantial traffic, environmental, and injury-reduction benefits of single-lane roundabouts.”
• Kansas State University Transportation Center (often cited study… focuses on impact on businesses as well as traffic safety/ flow)
  • https://www.mtjengineering.com/wp-content/uploads/2013/09/Study-of-the-Impact-of-Rbts-on-Traffic-Flows-Bus.-ksu0910_final.pdf
    • Quote: “…studies by Kansas State University of 11 other roundabouts in Kansas concluded that the roundabouts reduced stopping, queuing, delay and so forth 50 to 90% as compared to signals” (p. 107)

Hope you find this info helpful!