 In 2011, WSDOT calculated that the busiest section of the highway was the SR 500 concurrency in Orchards, serving 34,000 vehicles, while the least busiest section was at the western terminus of SR 503 Spur east of Yale, serving 720 vehicles.SR 503 between Orchards and Battle Ground is designated as part of the National Highway System, which includes roadways important to the national economy, defense, and mobility.SR 503 follows the route of State Road 15, established in 1909 as the Lewis River Road, traveling east from Woodland to the Skamania county line in Columbia National Forest.