| State Route 18 | ||||
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| Route information | ||||
| Defined by RCW 47.17.075 | ||||
| Maintained by WSDOT | ||||
| Length: | 28.41 mi[1] (45.72 km) | |||
| Existed: | 1964 – present | |||
| Major junctions | ||||
| West end: | SR 99 in Federal Way | |||
| SR 161 in Federal Way I-5 in Federal Way SR 167 in Auburn SR 164 in Auburn SR 516 in Covington SR 169 in Maple Valley I-90 near Snoqualmie |
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| East end: | SE Snoqualmie Parkway | |||
| Highway system | ||||
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State highways in Washington
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State Route 18, also known as SR 18 or Highway 18, is a 28-mile-long (45 km) state highway in the U.S. state of Washington, which connects State Route 99 in south King County with Interstate 90. It runs northeast from Federal Way, through Auburn, south Kent, Covington, Maple Valley, over the 1,375-foot (419 m) Tiger Summit, and then terminates at I-90 about 8 miles (13 km) east of Issaquah near Snoqualmie. This highway is the most direct route between Eastern Washington and Tacoma. North of I-90, Highway 18 becomes a local arterial, Snoqualmie Parkway. Snoqualmie Parkway continues to SR 202 just east of Snoqualmie Falls. This is the shortest route between I-90 and attractions at Snoqualmie Falls.
Highway 18 is a dangerous roadway[2] due in part to the heavy truck traffic between I-5 and I-90. For the past several years, work has been done on a project to turn SR 18 into a limited access highway and widen it to four lanes, two in each direction. Three-fourths of the highway upgrade has been completed; it now has four lanes from Federal Way to Issaquah Hobart Road. The last one-fourth of the expansion is 7 miles (11 km) which includes the climb up to Tiger Summit and the last 2 miles (3.2 km) to Interstate 90 with a freeway-to-freeway connection. The project still needs $267.5 million in funding and construction is set to be completed by 2015.
SR 18 forms part of one possible route for a proposed future Interstate 605, though the idea faces considerable opposition. However, some argue for renumbering the highway as an Interstate highway after completion of the widening, since it links Interstate 5 to Interstate 90.
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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.[3]
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).[4] 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.[5] 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 with in Auburn.[6]
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.[7]
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, use to be a signalized at-grade intersection before the reconstruction of SR 18,[8] 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.[9]
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.[10]
The entire route is in King County.[11]
| Location[11] | Mile[1] | Destinations | Notes |
|---|---|---|---|
| Federal Way | 0.00 | SR 99 (Pacific Highway) | |
| 0.21 | SR 161 south (Enchanted Parkway) – Puyallup | ||
| West end of freeway | |||
| 0.52 | I-5 – Seattle, Tacoma, Portland | ||
| 1.30 | Weyerhaeuser Way South | ||
| Auburn | 3.21 | West Valley Highway | Former SR 181 |
| 3.40 | SR 167 – Kent, Renton, Puyallup | Eastbound exit to SR 167 south is via West Valley Highway | |
| 4.35 | C Street Southwest | ||
| 4.68 | SR 164 east (Auburn Way) – Enumclaw, Auburn | ||
| 6.94 | Auburn-Black Diamond Road | ||
| 9.30 | Southeast 304th Street, Southeast 312th Street | ||
| Covington | 11.97 | SR 516 (Southeast 272nd Street) – Covington | |
| 13.65 | Southeast 256th Street | ||
| 16.22 | To SR 169 / Southeast 231st Street – Maple Valley | ||
| 18.49 | 244th Avenue Southeast | ||
| 20.84 | Issaquah, Hobart | ||
| East end of freeway | |||
| 24.11 | Tiger Mountain State Forest | ||
| 28.41 | I-90 – Seattle, Spokane | Interchange | |
| 28.41 | Snoqualmie Parkway | Continuation beyond I-90 to SR 202 | |
A band local to the Kent/Covington/Auburn area called Daphne Loves Derby wrote a song entitled Midnight Highway which sings "I miss our midnight rides on highway 18, 18 is gone."