Every year the Washington State Department of Transportation (WSDOT) conducts a series of surveys on its highways in the state to measure traffic volume. This is expressed in terms of average annual daily traffic (AADT), which is a measure of traffic volume for any average day of the year. In 2009, WSDOT calculated that as few as 1,100 cars traveled through the intersection with Bus Road just west of the Sunnyside Wildlife Recreation Area, and as many as 10,000 cars passed through the town of Toppenish before the interchange with US 97.