From the I-5 corridor to the mountain passes, Washington's highways run on mile markers. Here's how they work across the state, where they matter most, and how to see your exact one plus live WSDOT conditions in real time.

How Washington numbers its highways

Washington's mileposts count up from where a route enters the state and rise as you head north or east. On the interstates you'll see plain mile numbers on the shoulder. On state routes, WSDOT uses the SR format, so what a map might call Highway 520 is signed as SR 520. Mile marker data for every Washington highway is bundled into MileCheck and works offline.

The corridors people actually drive

  • I-5 runs the length of the state, about 276 miles from the Oregon border through Vancouver, Olympia, Tacoma, and Seattle up to the Canadian border.
  • I-90 crosses from Seattle east over Snoqualmie Pass toward the Idaho line, nearly 300 miles of it.
  • I-405 is the Eastside bypass around Lake Washington through Bellevue and Renton.
  • US-2 climbs over Stevens Pass; US-97 runs north to south east of the Cascades; US-101 loops the Olympic Peninsula.

Where mile markers matter most: the passes

Washington's mountain passes are where knowing your exact mile marker really counts. Snoqualmie Pass sits around mile marker 52 on I-90, and Stevens Pass on US-2 and White Pass on US-12 see the same fast-changing winter conditions. When a pass closes for weather or chains go into effect, the location is given by mile marker, and a breakdown in the snow is exactly the moment you need to tell help where you are.

MP 0 MP 100 MP 200 MP 300 · Idaho line Seattle Ellensburg Spokane Snoqualmie Pass · MP 52
I-90 climbs east out of Seattle over Snoqualmie Pass, around mile marker 52, before the long run to the Idaho line near mile 300.

Seasonal and weather closures

Washington closes highways more than most states. US-2 over Stevens Pass can shut for hours during winter storms and avalanche control. State Route 20, the North Cascades Highway, closes across a long stretch of the Cascades every winter and doesn't reopen until spring. Chinook and Cayuse passes close seasonally too. Every one of these is announced by milepost, so knowing the mileposts, and getting the live WSDOT alert before you commit to a pass, can save you a long backtrack over the mountains.

Live WSDOT alerts, in one place

MileCheck pulls live road alerts straight from WSDOT: closures, crashes, construction, and pass conditions, tied to the mile marker and direction so you can see what's ahead of you on your route. In Washington it also shows live Seattle drawbridge status for spans like the Fremont and Ballard bridges, so a raised bridge doesn't catch you mid-commute.

Everyday and emergency

Whether you're timing a mountain pass in January, reporting a breakdown on I-5, or just telling a friend where to meet you, the mile marker is the location Washington's roads run on. MileCheck shows yours in real time, down to a tenth of a mile, even where the cell signal drops.

Keep reading

Nearby state guides: Idaho  ·  Oregon

Washington drawbridges: every movable bridge, its opening rules and live status →

Essentials: What to tell 911 on the highway  ·  How to find your mile marker  ·  Browse the live mile marker map  ·  All 50 states