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Triangle Project: I-5 flyover ramps open early in Federal Way

A ribbon-cutting ceremony will be held July 16 to commemorate the completion of the Triangle Project, which refers to the interchange in Federal Way where Highway 161 (Enchanted Parkway), Highway 18 and Interstate 5 all meet. - Courtesy WSDOT
A ribbon-cutting ceremony will be held July 16 to commemorate the completion of the Triangle Project, which refers to the interchange in Federal Way where Highway 161 (Enchanted Parkway), Highway 18 and Interstate 5 all meet.
— image credit: Courtesy WSDOT

Construction on the $112.5 million Triangle Project is moving along at a swift pace and ahead of schedule.

Construction will be completed six months early and ready for the summer commuting season, according to the Washington State Department of Transportation.

The Triangle Project refers to the interchange in Federal Way where Highway 161 (Enchanted Parkway), Highway 18 and Interstate 5 all meet.

The interchange has long held a reputation for being dangerous for drivers. Federal Way and King County officials have been working to fund the project for more than a decade.

The WSDOT will host a ribbon-cutting ceremony Monday morning for the new flyover ramps on the project, which had an original completion date of April 2013.

Mowat Construction broke ground on the project in August 2010, and completed 26 concrete columns that will support the flyovers on the project.

The Triangle Project is in the first of two phases. The opening phase eliminated the cloverleaf loop ramps and replaced them with the flyover ramps for westbound Highway 18 to southbound I-5 and eastbound Highway 18 to northbound I-5.

Direct access will be provided to Highway 161 from southbound I-5 and westbound Highway 18 through the construction of new exit ramps at South 356th Street and South 359th Street in Federal Way.

According to WSDOT, when the I-5/Highway 18 interchange opened to traffic in the early 1960s, its cloverleaf design was state of the art in freeway design.

But the light traffic volumes during that time concealed the major flaw of the cloverleaf interchange: the weaving that occurs when traffic merges on and off the freeway. Weaving causes congestion and increases the potential for collisions.

In the past five years, 604 accidents have occurred on Highway 18 near the I-5 interchange, said Paula Hammond, WSDOT secretary.

During the 1960s, the two major thoroughfares each carried less than a quarter of the traffic they do now, according to WSDOT. The existing loop ramps are substandard and are high-accident locations.

The recent improvements will improve traffic flow and safety at this increasingly congested interchange.

The project will modify the I-5/Highway 18 interchange to eliminate weaving vehicle movements. The project is expected to improve existing and future traffic flow; reduce the number and severity of accidents in the vicinity of I-5, Highway 161 and Highway 18; and avoid or reduce the effects on the environment.

Crews also will build a new weigh-in-motion station so truck drivers have the option of bypassing the weigh station on southbound I-5 in Federal Way. Approximately 3,600 freight trucks — many coming to or departing from Federal Way — use Highway 18 to access Interstate 5 daily, according to WSDOT. The flyover ramps will cut down on the time it takes freight haulers to complete their runs.

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