The $112.5 million Triangle Project is moving along smoothly, 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 project is actually ahead of schedule for completion in “early fall of 2012,” according to Aleta Borschowa, a project engineer for WSDOT. Original estimates had the project opening to the public in April 2013. Mowat Construction broke ground on the two-and-a-half-year project in August.

“Right now, the project is a little ahead of schedule,” Borschowa said. “We are about a quarter of the way done and expect to be done with all the major work on the project by the end 2012. The contractor has been working very diligently.”

The project is currently in the first of two phases. The opening phase will eliminate the current cloverleaf loop ramps and replace them with 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.

Mowat Construction currently has completed 13 of the 26 concrete columns that will support the flyovers on the project, according to Borschowa.

There will be several lane and ramp closures until the project is complete, including some major shutdowns starting at the end of May.

Following Memorial Day, WSDOT will close down the westbound Highway 18 on-ramp to southbound I-5 for the entire summer.

The second large shutdown will occur on the westbound Highway 18 ramp to northbound I-5 during three weeks in August, Borschowa said. This will allow crews to raise the on-ramp 15 feet.

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.

“The cloverleafs are now a major impediment to moving vehicles,” Boschowa said.

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 numbers. The existing loop ramps are substandard and are high-accident locations. These 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 numbers. The flyover ramps will cut down on the time it takes freight haulers to complete their runs.

Lane closures

Until Friday, the carpool lane on southbound I-5 will close daily from 5 a.m. to 1 p.m. near Highway 18. Also, each direction of Highway 18 from Weyerhaeuser Way to I-5 will close nightly from 9 p.m. to 5 a.m. Ramp closures this week will include the eastbound and westbound ramps on Highway 18, along with northbound and southbound ramps from I-5 to Highway 18 will close nightly from 9 p.m. to 5 a.m.

More closures ahead

– Westbound SR 18 to northbound I-5 will close for three weeks starting Aug. 7

– Weyerhaeuser Way to SR 18 will be closed May 31 to late August

–  I-5 in Federal Way at SR 18 will undergo a series of intermittent overnight closures in October and November.

– On Sept. 1, 2011, the new ramp from westbound SR 18 to northbound I-5 will open