trains. The Mukilteo–Clinton ferry, operated by Washington State Ferries (WSF), takes approximately 20 minutes for each of its 39 daily round-trip crossings. , WSF charges a fare of $5.05 per walk-on passenger and $8.95 per vehicle during off-peak seasons, with varying fares depending on passenger age and vehicle size. SR 525 leaves the ferry terminal at Clinton and travels west through the interior of Whidbey Island in unincorporated Island County as part of the Whidbey Island Scenic Byway, a state scenic byway. The highway turns north along Holmes Harbor in Freeland and continues through Greenbank before SR 525 terminates at SR 20 south of Coupeville and the Naval Outlying Landing Field Coupeville. 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 2012, WSDOT calculated that the busiest section of SR 525 was its southern terminus at I-5 and I-405, serving 61,000 vehicles, while the least busiest section of the highway was at the Mukilteo ferry terminal, serving 5,700 vehicles. SR 525 is designated as part of the National Highway System from Lynnwood to the Mukilteo ferry terminal, classifying it as important to the national economy, defense, and mobility. WSDOT designates the entire route of SR 525 as a Highway of Statewide Significance, which includes highways that connect major communities in the state of Washington. History SR 525 uses the Whidbey Island Ferry between Mukilteo and Clinton, which began as a route of the Island Transportation Company in 1919. The ferry was later taken over by the Puget Sound Navigation Company, later sold to the state government in 1951 to form the WSF. The Mukilteo and Whidbey Island highways were added to the state highway system in 1937 as SSH 1D and SSH 1I, both branches of PSH 1. SSH 1D traveled on Whidbey and Fidalgo islands from the Clinton ferry dock to an intersection with the Anacortes branch of PSH 1 at Sharps Corner. It was later realigned on Whidbey Island in October 1959. SSH 1I traveled in a circular arc from Everett to Lynnwood, traveling on Mukilteo Boulevard and the Mukilteo Speedway. SR 525 was established during the 1964 state highway renumbering and codified in 1970 as the