 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.
