 SR 501 crosses a BNSF rail yard and enters the Port of Vancouver, becoming the Lower River Road and narrowing to a two-lane highway on the south side of Vancouver Lake.The highway follows the Columbia and Lake rivers north past the Shillapoo Wildlife Recreation Area, ending south of Post Office Lake in the Ridgefield National Wildlife Refuge.Every year, the Washington State Department of Transportation (WSDOT) conducts a series of surveys on its highways in the state to measure traffic volume.