Washington State Route 525

State Route 525
SR 525 is highlighted in red.
Route information
Auxiliary route of I-5
Maintained by WSDOT
Length	30.68 mi[1] (49.37 km) Mileage does not include ferry route
Existed	1964[2]–present
Tourist routes	Cascade Loop Scenic Byway Whidbey Scenic Isle Way
Major junctions
South end	I-5 / I-405 in Lynnwood
Major intersections	SR 99 in Lynnwood SR 526 in Mukilteo
North end	SR 20 near Coupeville
Location
Country	United States
State	Washington
Counties	Snohomish, Island
Highway system
State highways in Washington Interstate US State Scenic Pre-1964 1964 renumbering Former
← SR 524 → SR 526

State Route 525 (SR 525) is a 30.68-mile-long (49.37 km) state highway located in Snohomish and Island counties in the western region of the U.S. state of Washington. SR 525 begins at an interchange with Interstate 5 (I-5) and I-405 in Lynnwood and travels north to SR 99 as a four-lane controlled-access freeway. From Lynnwood, the highway serves Mukilteo and becomes the terminus of SR 526 before taking its ferry route to Clinton on Whidbey Island. SR 525 traverses the island's interior as part of the Whidbey Island Scenic Byway before the designation ends at an intersection with SR 20 south of Coupeville.

SR 525 was established during the 1964 state highway renumbering as the successor to Secondary State Highway 1D (SSH 1D) on Whidbey Island and SSH 1I in Mukilteo and Lynnwood, themselves established in 1937. The highway, at its codification in 1970, traversed the north–south length of Whidbey Island and ended at SR 536 near Anacortes until it was replaced by SR 20 in 1973. SR 525 was converted to its present freeway in Lynnwood during the 1980s and widened to four lanes during the late 1990s, including an overpass over SR 99. The highway also has a spur route in Mukilteo that has connected SR 525 to SR 526 via Paine Field Boulevard since it was signed in 2001.