Highways of Statewide Significance (HSS) include interstate highways and other principal arterials that are needed to connect major communities in the state. The designation helps assist with the allocation and direction of funding. The HSS was mandated by the 1998 legislature through enactment of House Bill 1487 (pdf 51 kb) and codified into RCW 47.06.140. In 1999 the legislature passed House Joint Memorial 4006 (pdf 9 kb) requesting that WSDOT, with the assistance of Regional Transportation Planning Organizations, update the HSS at least every five years.
The HSS was designated by the Transportation Commission through Resolution #660 on January 21, 2004. The Legislature concurred and adopted the HSS, including a map and route list through Engrossed House Bill 1433 (pdf 12 kb) on March 31, 2004. In 2006 the legislature adopted House Bill 3266 (pdf 11 kb) adding SR 169 to the route list of highways of statewide significance. In 2009 the legislature adopted SB 5642 adding SR 164 to the route list of highways of statewide significance.