State Road No. 1 Pacific Highway

State Road No.1 Pacific Highway was the main north-south highway in Washington State. This route started at the Interstate Bridge between Portland OR and Vancouver WA and headed northerly via Kelso, Chehalis-Centralia, Olympia, Tacoma, Seattle, Everett, Mount Vernon, and Bellingham to the US-Canadian border at Blaine. This route became US 99 in 1926. US 830 shared the same roadway with US 99 from Vancouver to Kelso. US 410 shared the same roadway with US 99 from Olympia to Tacoma. The designation in state law was changed to Primary State Highway 1 in 1937.

The Pacific Highway continued south from the Interstate Bridge through Oregon and California to the Mexican border and north from the Canadian border to Vancouver BC

Austin Pass Branch

The Austin Pass Branch of State Road No. 1 was added to the state highway system in 1925. This branch began at a junction with the trunk of State Road No. 1 in Bellingham and headed easterly to Austin Pass near Mount Baker. This route is commonly referred to as the Mount Baker Highway. The designation for this route in state law was changed to Primary State Highway 1-Austin Pass Branch in 1937.