Where does SR 18 begin? Is it Milepost 0 at Jct I-5 Exit 142? Is it Milepost 0B at Jct SR 99? No, in theory, SR 18 begins in Tacoma at Jct SR 509 near the Marine Dr, Taylor Way intersection. On paper, SR 18 is to be a continuation of the SR 509 freeway in the port of Tacoma area, climbing a gulch from the flats to Federal Way, then heading east to connect with the existing route. Originally designated as the Auburn-North Bend Branch of PSH 2, costruction began between Federal Way and Auburn in the late 1950s. By late 1962, PSH 2 AN had extended from US 99 to the Issaquah-Hobart Rd interchange. In January 1964, the route was renumbered SR 18. The Issaquah-Hobart Rd to I-90 section via Tiger Summit opened in January 1965. Widening of this mostly 2 lane route to 4 lanes began from Federal Way. By the mid 1970s, SR 14 was 4 lane divided from SR 99 to SR 164. In 1986, 4 lanes were extended to the Auburn-Black Diamond Rd interchange. In the 1990s, additional lanes were added as far as 180th Ave SE, a mile NE of Jct SR 516. The 180th Ave NE to Maple Valley section of SR 18 will be upgraded to 4 lane freeway by early 2003. Interchanges and realigned intersections with traffic signals have cut the fatality rate. Perhaps SR 18 will be 4 lane divided freeway from I-5 to I-90 within the next decade. SR 18, minus the SR 509 to SR 99 portion, is 28.41 miles long.
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