High Quality Content by WIKIPEDIA articles! Interstate 90 (I-90) is the longest Interstate Highway in the United States at 3,099.07 miles (4,987.47 km). It is the northernmost coast-to-coast interstate, and parallels US 20 for the most part. Its western terminus is in Seattle, at Edgar Martinez Drive S. near Safeco Field and CenturyLink Field, and its eastern terminus is in Boston, at Route 1A near Logan International Airport. Interstate 90 also goes through Spokane and crosses the Continental Divide over Homestake Pass just east of Butte, Montana.