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SR 9 - SR 531 / 172nd St NE - Intersection Improvements - Design Options

July 2009

Design options
We displayed the following preliminary design options at July 21, 2009, open house. The options included an improved signal or a roundabout. The design visuals below do not include all features or exact measurements that the finished design will.


Improved signal option
With this option, we would widen SR 9 to seven lanes at the intersection to include two left turn lanes for northbound and one left turn for southbound drivers, two through lanes in each direction, and one right turn lane in each direction. And, we would widen SR 531 to five lanes at the intersection to include one right turn lane in each directions, one through lane in each direction, and one left turn lane in each direction. 

A new signal is an option
Visit our flickr page to see an enlarged version of the signal option.

Signal strengths

  • Improves mobility
  • Shortens delays
  • Drivers are familiar with signals

Signal weaknesses

  • Severity of collisions increase with higher speeds
  • Lengthy delays by 2033
  • Have to widen SR 9 to 7 lanes and SR 531 to five lanes
  • Moderate changes to private access around intersection


Roundabout option

With this option we would widen the each leg of the intersection intersection to four lanes to provide two lanes in every direction.

A roundabout is one design option
Visit our flickr page to see an enlarged version of the roundabout option.

Roundabout strengths

  • Significantly improves safety: Fewer collisions, injuries and fatalities
  • Widen SR 9 and SR 531 to four lanes
  • Expected to move drivers efficiently beyond 2033
  • Minor changes to private access around intersection

Roundabout weaknesses

  • Drivers may be unfamiliar with roundabouts
  • Traffic slows down through intersection
  • Does not match other intersection improvements on SR 9


An aerial view of the current intersection.

Existing intersection
Visit our flickr page to see an enlarged version of the existing intersection.