Washington State Route 18 - Route Description

Route Description

Washington State Route 18 (SR 18) begins as South 348th Street at a signalized interchange with SR 99 (Pacific Highway). Heading due east, SR 18 comes to a second traffic light at SR 161 (16th Avenue South / Enchanted Parkway), providing access to Federal Way and Wild Waves Theme Park. SR 18 becomes a full freeway and the first grade separated interchange is a full cloverleaf interchange with Interstate 5 (I-5), providing access to Seattle and Vancouver, British Columbia to the north, and Tacoma and Portland, Oregon to the south. A diamond interchange with Weyerhaeuser Way reduces the number of lanes to two each direction as the highway descends into Peasley Canyon.

After exiting the canyon, a complex hybrid partial cloverleaf interchange / diamond interchange with the West Valley Highway (former SR 181) and an almost complete cloverleaf interchange SR 167 occurs, with traffic from eastbound SR 18 only being able to access SR 167 via the West Valley Highway. This interchange is the highest traffic point on SR 18, with a daily average of 88,000 cars-per-day traveling along SR 18 at this interchange (a slight decrease from 93,000 in 2007, and 89,000 in 2006). Traffic has more than sextupled since 1967, the first entry for SR 18 in the annual traffic log, with only 14,500 cars-per-day passing through this intersection. The SuperMall of the Great Northwest, which has direct access ramps onto SR 167 and SR 18 passes to the south of SR 18. Union Pacific Railroad, former Northern Pacific Railroad, tracks and the mixed-use Interurban Trail pass underneath SR 18 as it approaches a folded cloverleaf interchange with C Street Southwest in Auburn. SR 164 (Auburn Way South) is accessible by a partial cloverleaf / diamond interchange, and is the final exit within Auburn.

Another folded cloverleaf interchange provides access to Green River Community College, Auburn Narrows Park and Hatchery Park via Southeast Auburn-Black Diamond Road. The highway passes over the Green River and parallels Big Soos Creek as it climbs into an interchange with Southeast 304th Street in unincorporated King County. Entering Covington, SR 18 intersects SR 516 (Southeast 272nd Street / Kent Kangley Road). 180th Avenue Southeast (Souheast Wax Road) is the next interchange before SR 18 passes over Jenkins Creek, and then an interchange with Southeast 256th Street.

A diamond interchange provides access to Maple Valley before the route continues northerly and crosses over the Cedar River and through an interchange with 244th Avenue Southeast. An overpass, carrying Southeast 200th Street, used to be a signalized at-grade intersection before the reconstruction of SR 18, passes over the highway as it approaches the Issaquah-Hobart Road serving the cities of Issaquah and Hobart as well as the Mirrormont residential community between Issaquah and SR 18 at the base of Tiger Mountain.

SR 18 becomes an at-grade roadway again, and climbs towards Tiger Summit, a pass through the Issaquah Alps which, at elevation 1,377 ft (420 m), is the highest point along the road, with a parking area to the north of the highway that allows access to a trail head that leads to a hang gliding point. Continuing down the summit the highway passes over the Raging River and Lake Creek before an at-grade interchange with Southeast 104th Street (Rattlesnake Road SE). The final interchange of SR 18 is a fully signalized diamond interchange with I-90, providing access to Issaquah and Seattle to the west and North Bend and Spokane to the east. The roadway continues past the interchange as Snoqualmie Parkway where it terminates at SR 202 in Snoqualmie.

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