Local Information

New ramp meters to bring I-5 congestion relief to south King County

Monday, July 22, 2013 - 10:40

Bart Treece, WSDOT communications, 206-440-4473 (Shoreline)

TUKWILA – Traffic will soon move a little smoother along eight miles of Interstate 5 between Tukwila and Federal Way with the help of several new ramp meters – which are traffic signals that manage the flow of merging vehicles onto the highway.

During the past 12 months, contractor crews working for the Washington State Department of Transportation installed ramp meters at four separate interchanges where traffic routinely slows to a crawl during the morning and afternoon rush-hour commutes. New meters at these interchanges, along with those previously installed at the South 320th Street interchange from an earlier project, will turn on Monday, July 29.

“Ramp metering is a proven, cost-effective approach to reducing freeway congestion and collisions, providing drivers a better, more reliable trip,” said Mark Leth, WSDOT traffic engineer.

A ramp meter is a traffic signal that operates according to real-time conditions on both the freeway and the ramp. They help reduce congestion by providing consistent gaps between vehicles, rather than allowing multiple vehicles to flood the freeway at once.

“Think of it as waiting in line; it’s far better to have folks take their turn rather than let everyone try to get served at once.” added Leth. “When drivers take their turn and enter traffic at an even pace, the freeway flows better and merge-related crashes are decreased. Ramp meter systems have proven to reduce collisions by 30 percent.”

WSDOT expects the ramp meters will improve the current 40 mph commute speeds during peak periods along this I-5 segment. It also allows freeway engineering staff to immediately respond to freeway incidents.

The newly installed ramp meters are located on the following ramps:

  • South 188th Street to northbound I-5
  • South 188th Street to southbound I-5
  • South 200th Street to southbound I-5
  • State Route 516 westbound to northbound I-5
  • SR 516 eastbound to northbound I-5
  • SR 516 to southbound I-5
  • South 272nd Street to northbound I-5
  • South 272nd Street to southbound I-5

Ramp meters installed under previous contracts that will be activated are located on the following ramps:

  • South 320th Street eastbound to northbound I-5
  • South 320th Street westbound to northbound I-5
  • South 320th Street to southbound I-5

In addition to the ramp meter installations, the northbound and southbound single-lane on-ramps at South 188th Street were revised to double-lane ramps. Traffic sensors were installed on both the ramps and freeway lanes to enable real-time monitoring of the metering operation and automatic adjustments to reflect current conditions. Crews also installed warning lights, signing and new lane striping as part of the overall ramp metering system.

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