SR 150 - No See-Um Road Intersection Improvements - Project design

Roundabout Alternative

Before and after rendering (pdf 456 kb)

  • Advantages - fewer conflict points at the intersection and no left turn conflict points; reduced wait times on side streets; reduced collision severity; lower exhaust emissions; reduced annual maintenance expenses. 
  • Disadvantages - slows SR 150 traffic to below 25 mph. 
  • Collisions - Reduces injury collisions by 70%. 

An inherent design feature of roundabouts is that they eliminate high speed left turn and right angle conflicts which are the ones that result in the most serious "T bone" collisions.

According to the Insurance Institute for Highway Safety , roundabouts have been shown to reduce fatal collisions by 90 percent, injury collisions by 80 percent and total collisions by almost 40 percent.

Something you may not know about roundabouts involves how trucks get through them properly courtesy of what's called a truck apron. That's the raised, circular concrete part around the center of a roundabout. It acts like an extra lane for large vehicles. So when you're driving a roundabout, and see a trailer riding up on that raised concrete circle, don't worry. That's what it's there for. (See the pictures and video). To learn more, watch how do I drive a roundabout video on YouTube and visit WSDOT's roundabout website.

Full size RAB Des/Vis

Full Design/Visualization Version (pdf 1056 kb)