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SR 150 - No See-Um Road Intersection Improvements Alternatives

After six years of analysis, two alternatives to address the congestion and safety issues associated with the No See-Um Road intersection remain.

#1 - Construct left turn lanes and a right turn pocket on SR 150 at the intersection, relocate the intersection to the west, tie Spader Bay Road into the relocated intersection as the south leg, relocate SR 150 to the south. 

Left Turn Alternative

  • Advantage -  addresses  turning traffic on SR 150; increases sight distance at the intersection; reduces rear end accidents at intersection. 
  • Disadvantages - potentially increases at angle collisions by widening the roadway, extending the time needed to cross it; increase grade on SR 150; increased property impacts due to realignment of road.
  • Collisions - addresses rear end collisions where traffic is stopped on SR 150 waiting to make left turns onto No-See-Um Road.
  • Estimated Total Cost - ($9.23 million)


#2 - Construct a roundabout at SR 150 and No See-Um Road west of the existing intersection that would include Spader Bay Rd tieing in from the south. 

Roundabout Alternative

  • Advantages - fewer conflict points at the intersection and no left turn conflict points; reduced wait times on side streets; reduced collision severity; reduced annual maintenance expenses. 
  • Disadvantages - slows SR 150 traffic to below 25 mph; property impacts on south side of SR 150. 
  • Collisions - addresses all types of collisions.  Reduces injury collisions by 70%. 
  • Estimated Total Cost - ($4.9 million)

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 .