 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 2 @,@ 000 cars traveled through the central part of the highway , and as many as 2 @,@ 500 cars at the interchange with SR 22 . 
