Interstate 90 is the longest interstate highway in the United States, running 3,020 miles from Seattle, Washington to Boston, Massachusetts. It is the northern transcontinental backbone, paralleling I-94 across Montana and the upper Midwest, then taking on the role of 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 most heavily-trucked Cascade pass — 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 alone closes 10-20 times per winter, 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 most heavily-trucked Cascade crossing
  • Highest point: Beartooth area in Montana / Bozeman Pass at 5,712 ft
  • Crosses the Mississippi River at La Crosse, WI