New ramp meters to ease congestion on I-5 in south King County

New ramp meters will help smooth traffic flow and ease congestion along eight miles of Interstate 5 between Tukwila and Federal Way.

The Washington State Department of Transportation will install ramp meters at four separate interchanges where traffic routinely slows to a crawl during the morning and afternoon rush-hour commutes. New meters at all four interchanges should be in place and easing congestion by summer 2013.

The average morning commute speed for northbound traffic is 37 mph between Federal Way and Tukwila. And it’s 40 mph southbound for the evening commute. When traffic signals at intersections near these ramps turn green, a dozen or more cars enter I-5 at the same time, further clogging already-slow traffic on the interstate.

“Heavy traffic from the ramps tends to overload the interstate in these areas during rush hour,” said Mark Leth, WSDOT traffic engineer. “Ramp meters will release them onto the interstate in a controlled manner. Ramp meters are a cost-effective and proven method to manage demand and operate the highway system efficiently to keep traffic moving during peak commutes.”

Ramp meters are proven to reduce collisions by at least 30 percent. Every minute a lane is blocked by a collision or other incident adds four to 10 minutes of traffic delay, so reducing collisions at these merge areas also reduces congestion.

Contractor crews working for WSDOT will begin work to install meters along northbound and southbound I-5 beginning Monday, Aug. 20. The new meters will be located on the following ramps:

S 188th Street to northbound I-5

S 188th Street to southbound I-5

S 200th Street to southbound I-5

State Route 516 westbound to northbound I-5SR 516 eastbound to northbound I-5

SR 516 to southbound I-5

S 272nd Street to northbound I-5

S 272nd Street to southbound I-5.

During the work, drivers can expect daytime lane closures near each interchange and overnight ramp closures.

Along with ramp meters, crews will restripe the northbound and southbound single-lane on-ramps at S 188th Street to double-lane ramps and install traffic-detection loops on the interstate. The loops send a continuous stream of data to the ramp meters, so they can automatically adjust their cycles to best manage traffic flow. Other improvements include installing flashing amber warning signals on the ramps, restriping and adding signs.

The new ramp meters will be used in coordination with sever

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