 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 2011 , WSDOT calculated that between 4 @,@ 100 and 21 @,@ 000 vehicles per day used the highway , mostly between Sumner and Orting . 
