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 513 was within the University of Washington campus, serving 41,000 vehicles, while the least busiest section was its northern terminus at Magnuson Park, serving 14,000 vehicles. The entire route of SR 513 is part of the National Highway System, identifying it as important to the national economy, defense, and mobility. History SSH 1J, the predecessor to SR 513, was added to the state highway system in 1937 and traveled within the city of Seattle on streets that have existed since the 19th century. Madison Street, which carried SSH 1J from its southern terminus at U.S. Route 99 in Downtown to Capitol Hill was built in 1864 by local judge John J. McGilvra to connect his homestead at Madison Park to downtown. Other streets carrying SSH 1J, including 23rd and 24th Avenues towards Montlake, Montlake Boulevard through the University District, and Sand Point Way towards Sand Point were built during the early 1890s as the city of Seattle expanded. The rest of SSH 1J, traveling northwest from Naval Station Puget Sound at Sand Point through Lake City to US 99 on the border between Seattle and Shoreline via Roosevelt Way and 145th Street was constructed by the late 1800s to serve the University of Washington campus, site of the Alaska–Yukon–Pacific Exposition in 1909. SSH 1J was replaced by SR 513 during the 1964 state highway renumbering and codified in 1970 on its original route, connecting Downtown Seattle to Montlake and Lake City. In 1971, SR 513 was shortened to by moving its southern terminus to an interchange with SR 520 in Montlake and its northern terminus to an interchange with I-5 at 145th Street. The highway was further shortened, to its present length of , in 1991 by moving its northern terminus from I-5 to Magnuson Park at the site of the former Naval Station Puget Sound. Major intersections References External links Highways of Washington State 513 Transportation in King County, Washington Transportation in Seattle