I-90: The Northern Tier Transcontinental

Interstate 90 is the longest interstate highway in the United States, running 3,020 miles from Seattle, Washington to Boston, Massachusetts. It is the main northern transcontinental route, running parallel to I-94 across Montana and the upper Midwest, then becoming the principal east-west corridor through the Great Lakes states and the Berkshires.

The geography is varied. From Seattle, I-90 climbs over Snoqualmie Pass (3,022 ft), the main freight route across the Cascades and Washington's only interstate-grade, year-round Cascade crossing (WSDOT), then crosses the Columbia Plateau, climbs the Bitterroot Mountains at Lookout Pass (4,711 ft) on the Idaho-Montana border, threads the Bozeman Pass and the Crow Indian Reservation, rolls across the Great Plains of Wyoming and South Dakota (with a brief brush past the Badlands), passes through Minnesota, and meets up with I-94 in Wisconsin. From Chicago east, I-90 follows the Indiana Toll Road, the Ohio Turnpike, and the Pennsylvania Turnpike to the New York Thruway, which carries it through Buffalo, Syracuse, Utica, and Albany, before becoming the Massachusetts Turnpike to Boston.

For freight, I-90 is the principal route between the Pacific Northwest ports and the Great Lakes industrial belt. It is also one of the most heavily-tolled interstates. Virtually every mile east of Chicago is a toll road. Winter conditions across the western half are severe; Snoqualmie Pass closes repeatedly for avalanche control and crashes, and the Wyoming and South Dakota stretches see frequent ground-blizzard closures.

• Longest US interstate at 3,020 miles
• Crosses thirteen states: WA, ID, MT, WY, SD, MN, WI, IL, IN, OH, PA, NY, MA
• Concurrent with I-94 across most of southern Wisconsin and northern Illinois
• Tolled across IN, OH, PA, NY, and MA, among the most-tolled interstate corridors
• Snoqualmie Pass (3,022 ft) is the main freight route over the Cascades, about 28,000 vehicles a day, roughly 5,600 of them freight (WSDOT)
• Highest point: Beartooth area in Montana / Bozeman Pass at 5,712 ft
• Crosses the Mississippi River at La Crosse, WI

The passes on Interstate 90 with a full guide: grade, chain-control season, closures and hazards. The status is the state DOT's latest reading.

• Snoqualmie Pass, Washington, 3,022 ft: No live data
• Lookout Pass, Idaho / Montana, 4,710 ft: Open
• Fourth of July Pass, Idaho, 3,069 ft: Open
• Homestake Pass, Montana, 6,375 ft: Open
• Bozeman Pass, Montana, 5,712 ft: No live data

Chain rules for the states these passes are in, and for every state on the route that has a chain law:

• Washington chain law
• Idaho chain law
• Montana chain law
• Wyoming chain law
• Pennsylvania chain law
• Massachusetts chain law

National Weather Service alerts in force in the states Interstate 90 runs through. Each one covers a county or a forecast zone, which may be far from the Interstate.

• 1 alert in Montana: Special Weather Statement
• 12 alerts in New York: Coastal Flood Warning, High Wind Warning, Wind Advisory
• 8 alerts in Massachusetts: Coastal Flood Advisory, Coastal Flood Warning, Flood Watch, High Wind Warning, Wind Advisory