 The highway terminates at a roundabout with SR 9 near a gun range south of downtown Arlington.SR 531 is maintained by the Washington State Department of Transportation (WSDOT), which conducts an annual survey on the state's highways to measure traffic volume in terms of average annual daily traffic.In 2016, WSDOT calculated that the busiest section of the highway is located in Smokey Point and carried an average of 24,000 vehicles per day.