 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 the busiest section of SR 100 was its terminus at US 101 in Illwaco , serving 2 @,@ 100 vehicles , while the least busiest section was the intersection with its spur route in Cape Disappointment State Park , serving 650 vehicles . 
