I-90's Western Terminus: Where the Longest Interstate Begins

Interstate 90 begins in Seattle. Its western terminus is at Washington State Route 519 and 4th Avenue South, in the SoDo neighborhood south of downtown. The junction sits next to the Port of Seattle and two major sports stadiums, Lumen Field and T-Mobile Park. From there the freeway runs all the way to Boston, Massachusetts, where it ends at Massachusetts Route 1A near Logan International Airport. [1]

It is the longest Interstate Highway in the United States, at 3,099.7 miles. It serves 13 states and has 15 auxiliary routes, and 296.92 of its miles are in Washington. It crosses the Cascade Range in Washington and the Rocky Mountains in Montana, follows the southern shore of Lake Michigan through the Chicago area, and roughly follows the historic Erie Canal across New York. [1]

The route is older than the number. The Federal-Aid Highway Act of 1956 established the freeway, replacing a series of U.S. Highways that had been preceded by local roads and auto trails. Among those trails were the transcontinental Yellowstone Trail and National Parks Highway, created in the 1910s along the future route between Seattle and Boston. Out of Seattle, the numbered highway it replaced was US 10, which ran to Billings, Montana. I-90 was numbered in 1957, reflecting its status as the northernmost transcontinental route of the system. [1]

Seattle's end was the last piece built. Washington was the last state to complete its section of I-90, mainly because of disputes and litigation over the Seattle to Bellevue stretch. The extension into Seattle was completed in stages between 1989 and 1993 and cost $1.56 billion. It took a new floating bridge, an expanded Mount Baker Ridge Tunnel, lids with parks, and extensive mitigation for environmental and social impacts. It was meant to be finished in 1992, but the original floating bridge sank during renovations in November 1990. The rebuilt bridge opened to eastbound traffic on September 12, 1993, and the final section, near the western terminus, opened that September. [1]

Even the starting line was later rebuilt. In the early 2000s, the west end at SR 519 was turned into a series of ramps near Safeco Field, now T-Mobile Park, replacing an existing intersection. Heading east from it, I-90 passes an interchange with I-5, goes around Beacon Hill and enters the Mount Baker Ridge Tunnel alongside the 2 Line of the Link light rail system. It comes out onto a pair of floating bridges, among the longest of their kind: the eastbound-only Lacey V. Murrow Memorial Bridge and the Homer M. Hadley Memorial Bridge, which carries westbound traffic and the light rail tracks. Washington has designated its section the American Veterans Memorial Highway. [1]