 Under a 1909 law , the State Highway Board surveyed a connected network of proposed state roads . Included was a westerly extension of SR 5 via Chehalis to South Bend and Aberdeen and an easterly extension to Pullman . A route from Yakima southeast and east via the Tri @-@ Cities to Idaho was also surveyed , mostly as an extension of State Road 8 ( Columbia River Road ) . The legislature added most of these routes to the state highway system in 1913 , when they formed a two @-@ tiered system of primary and secondary roads . Primary roads were completely controlled by the state , including maintenance , and received only names , while secondary roads kept their numbers and county maintenance . The National Park Highway replaced State Road 5 west of Riffe , and extended as surveyed to and beyond South Bend , and the McClellan Pass Highway replaced State Road 1 and continued via State Road 5 to Yakima . The majority of the route from Yakima via Connell to Pullman was not added at that time ; it was finally taken over in 1937 as Secondary State Highways 11A and 11B . Only the route via the Tri @-@ Cities , forming part of the Inland Empire Highway , continued from Yakima to Idaho . East of Pomeroy , the original survey had curved south , using State Road 16 to near the Oregon state line ; this was bypassed by the 1913 designation , which instead continued directly east to Clarkston . Unlike the earlier state roads , these primary roads mostly followed existing passable county roads . The incomplete roadway between Riffe and the American River remained as part of secondary State Road 5 , and the legislature designated the surveyed route from the National Park Highway near Raymond north to Aberdeen as secondary State Road 20 in 1915 . 
