 Every year , 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 27 was its interchange with I @-@ 90 in Spokane Valley , serving 27 @,@ 000 vehicles , while the least busy section was between Tekoa and Latah , serving 640 vehicles . 
