We recently reconstructed the roundabout at West Lake Sammamish Parkway and  Lakemont Boulevard near I-90 in order to replace the failing pavement and improve drainage. WSDOT also enlarged the size of the roundabout in order to improve safety and increase capacity in the roundabout. While these revisions have resulted in increased capacity in the roundabout for afternoon drivers, we are experiencing substantial delays through the intersection for an hour on weekday mornings. We are working on implementing some solutions for reducing morning backups.

New traffic metering signal Thursday
A new traffic signal will begin operating during Thursday's morning rush hour on the south leg of the roundabout for drivers coming from Lakemont Boulevard. The signal will resemble a freeway ramp meter so that vehicles coming from Lakemont Boulevard will stop briefly before entering the roundabout. The brief stop will create gaps in the stream of traffic making it easier for drivers to merge into the  roundabout from the other legs of the roundabout and reducing the lengthy backups on W. Lake Sammamish Parkway. We expect that this signal will work better than the existing flaggers because it will direct vehicles more efficiently and avoid the delay that occurs while flaggers alternate between each leg. Clearly, there will still be a line up of vehicles during the busy commute hours, but traffic should flow more smoothly with less delay.

Right turn lane
We are working to reestablish a right turn lane from westbound W. Lake Sammamish Parkway to northbound W. Lake Sammamish Parkway. Our engineers are currently trying to design the new right turn lane to meet safety requirements, yet stay within our existing right-of-way. Our goal is to have the new right turn lane constructed and open to traffic by the end of the year.

Evening commute benefits
Since reopening the roundabout, evening commute traffic flow has improved. During evening rush hours the roundabout is carrying roughly 200 more southbound vehicles per hour, which is more than a 20-percent increase in traffic.

We appreciate your patience while we work to deliver the best solution for this intersection. For more information, please visit our project web page

http://www.wsdot.wa.gov/projects/i90/SammamishRoundabout

We will provide additional updates as new information develops.

Sincerely,

Lorena Eng 
Northwest Region Administrator 
Washington State Department of Transportation 
(206) 440-4706