When first posted as such in January 1964, SR 525 began at Jct US 99 (now SR 99) north of Lynnwood and headed north via the Mukilteo Speedway to the Mukilteo ferry terminal. On the other side of Possession Sound, SR 524 continued at Clinton and headed north along the entire length of Whidbey Island via Coupeville and Oak Harbor to the Deception Pass Bridge. Crossing the bridges over Deception and Canoe Passes, SR 525 continued north to Jct SR 536 at Sharps Corner and ended.
In January 1965, I-5 opened through SW Snohomish County. SR 525 was extended from US 99 via existing roads to I-5 Exit 183. In 1973, after the completion of the North Cascades Highway, SR 20 was extended west from Jct SR 536 at Fredonia to Jct US 101 at Discovery Bay. This extension included renumbering SR 525 from Jct SR 113 south of Coupeville on Whidbey Island to Jct SR 536 at Sharps Corner as part of SR 20. SR 113 was also renumbered SR 20. Circa 1980, SR 525 from SR 99 to I-5 was moved to a 2 lane freeway interchanging with I-5 at Exit 182. In late 1999, an interchange was completed at the SR 99/SR 525 junction. Construction is underway in 2001 to widen the SR 525 2 lane freeway from I-5 to SR 99 into 4 lanes divided. Today, SR 525 is 30.68 miles long.
Before 1964, SR 525 from US 99 to Mukilteo had been part of SSH 1I and from Clinton to Sharps Corner, SSH 1D.
The 2001 state legislature added Paine Field Blvd to the state highway system as a spur of SR 525. Paine Field Blvd provides a shortcut for northbound Sr 525 traffic headed for eastbound SR 526 and west 526 to south SR 525. In my opinion, this route acts as an SR 526 spur, not a 525 spur. This spur was added after the 2001 State Highway Log was published, thus the length of this new spur is not listed.
Primary State Hwys Secondary State Hwys