Interstate 90 is the longest freeway in America, stretching over 3,000 miles coast-to-coast.

Countries & Cities · Published 3 October 2026 Swipe more like this →

In short: Spanning 3,099.7 miles from Seattle to Boston, Interstate 90 is the backbone of northern American transit. Established by the 1956 Federal-Aid Highway Act, this transcontinental route traverses 13 states, climbing the Rockies and skirting the Great Lakes, serving as a vital artery for both commerce and cross-country travel.

Conceived as the northernmost transcontinental route of the Interstate system, I-90 was officially numbered in 1957. Its path replaces a legacy of 20th-century auto trails and U.S. Highways, weaving together diverse landscapes from the Pacific Northwest to the Atlantic coast. The route reaches its highest elevation at Montana's Homestake Pass, standing at 6,329 feet, while its western terminus in Seattle features floating bridges across Lake Washington that rank among the longest of their kind.

The highway's construction was a decades-long endeavor. While Midwestern sections were largely finished by 1978, the final piece of the original route near Seattle opened in September 1993. The project's eastern reach was further extended in the early 2000s through Boston's Big Dig, a massive infrastructure undertaking that added 3.5 miles to the freeway, culminating at Logan International Airport. Today, roughly 25 percent of the route consists of toll roads, including the Massachusetts Turnpike and the New York State Thruway.

Traffic patterns on I-90 vary wildly, reflecting the diverse regions it serves. In 2011, the Federal Highway Administration recorded a daily average of 306,574 vehicles on the busiest section in Chicago, while rural stretches in Wyoming saw as few as 9,820. The freeway also serves as a historical corridor, passing sites like the Battle of the Little Bighorn in Montana and following the path of the 19th-century Erie Canal through New York, grounding modern transit in the geography of American history.

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