The Alaskan Way Viaduct was one of two north–south freeways traversing Downtown Seattle, the other being Interstate 5 to the east. Traffic volumes on the viaduct, measured by WSDOT in terms of average annual daily traffic in 2015, averaged approximately 91,000 vehicles south of Columbia Street and 71,000 vehicles between Columbia Street and Western Avenue. The viaduct formerly carried an average daily volume of 110,000 vehicles until the start of demolition in 2011. The viaduct and other sections of SR 99 were designated as part of the National Highway System by the federal government and as Highway of Statewide Significance by the state legislature.