Washington State Route 539

State Route 539
Guide Meridian
SR 539 highlighted in red
Route information
Auxiliary route of I-5
Maintained by WSDOT
Length	15.18 mi[1] (24.43 km)
Existed	1969–present
Major junctions
South end	I-5 in Bellingham
Major intersections	SR 546 near Lynden
North end	Hwy 13 at Canada–United States border near Lynden
Location
Country	United States
State	Washington
Counties	Whatcom
Highway system
State highways in Washington Interstate US State Scenic Pre-1964 1964 renumbering Former
← SR 538 → SR 542

State Route 539 (SR 539, named the Guide Meridian) is a north–south state highway in the U.S. state of Washington. The highway travels through northwestern Whatcom County and connects Interstate 5 (I-5) in Bellingham with Lynden and the Canadian border near Langley, British Columbia.

The Guide Meridian, named for the guide meridian that it follows while traveling due north–south, was originally a plank road constructed in the late 1880s. It was replaced with a gravel road in the 1910s and a paved highway later that decade by the Whatcom County government. The Guide Meridian was absorbed into the state highway system and designated as Secondary State Highway 1B (SSH 1B) in 1937, which was later supplemented with the creation of U.S. Route 99 Alternate in 1952. Both designations were replaced with SR 539 in 1969 following the completion of I-5 in Bellingham.

The majority of SR 539 between Bellingham and Lynden was expanded to a four-lane highway with turn lanes over two phases in the late 2000s. The project included construction of several roundabouts and a new bridge over the Nooksack River near Lynden on an accelerated schedule to accommodate traffic ahead of the 2010 Winter Olympics in Vancouver.