What is Washington State’s Longest Highway?

Pop quiz. Before scrolling down, what is the longest highway in Washington State? 

My first two guesses are I-90 from Seattle to the Idaho border or US Highway 2 from Everett to the Idaho border. Let's go over those two guesses. 

I-90 in Washington

I-90 begins its eastward Washington journey at the intersection of Edgar Martinez Drive South and 4th Avenue South, home of the Seattle Mariners. I-90 crosses the Cascades at Snoqualmie Pass and continues through Spokane and Spokane Valley. It ends in Washington, following the Spokane River to the Idaho state line. I-90’s time in Washington clocks in at 297.51 miles. I-90 runs from Seattle to Boston, spanning at 3,021 miles. Here are the more interesting things you’ll find on the long cross-country drive.

US 2 in Washington

US 2’s time in Washington begins in Everett, crossing the Cascades at Stevens Pass. It passes through the Columbia River at Wenatchee, then up Pine Canyon to the wheat fields of Waterville. After passing through Spokane, the highway’s time in Washington wraps up in Newport before entering the state of Idaho. US 2’s distance in Washington is 326.34 miles. 

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Overall, US 2 traverses the US and Canada, from Everett to Maine—2,571 miles across the northern continental United States. It consists of two segments connected by several roadways in southern Canada.

US 12 in Washington

US 12 begins in Aberdeen and crosses the Cascades at White Pass. It then goes through Eastern Washinton, passing through Yakima, the Tri-Cities, and Walla Walla. After nudging north into Dayton, it runs through Pomeroy and ends its time in Washington in Clarkston before crossing into Lewiston, Idaho. The highway spans 430.5 miles across Washington, making it the second-longest road in the state.

State Route 20 in Washington

I hadn’t considered this route. State Route 20 begins on the Olympic Peninsula, just south of Port Townsend. It technically crosses Puget Sound via the Washington State Ferry system to Coupeville on Whidbey Island. Then, it makes its way to the North Cascades Highway - typically closed in the Winter - due to the usual heavy snowfall in the Cascade Mountains. The route stays north, taking a turn slightly south just after crossing the Columbia River near Kettle Falls. SR-20 ends in Newport, WA. State Route 20 runs 436.16 miles—the longest stretch of highway in Washington...barely nipping US 12 by 5 miles.