Washington
Idaho
Montana
Wyoming
South Dakota
Minnesota (PART 1/PART 2)
Wisconsin (PART 1/PART 2)
Illinois
Indiana
Ohio
Pennsylvania
New York
Massachusetts
This is said to be the longest Interstate highway, connecting Boston to Seattle. However, it has been discovered that the Chicago Skyway is not an Interstate-compatible section, so that would make I-80 the longest continuous interstate.
From Chicago to Cleveland, I-90 is multiplexed with I-80.
Instead of increasing to the east, the mile markers on I-90 in New York State actually decrease, in part because the majority of it follows the New York State Thruway. On even-numbered interstates, mileage increases to the east and decreases to the west. On odd-numbered interstates, the mile markers increase to the north and decrease to the south.
In Cleveland, OH, I-90 enters Dead Man's Curve. Because it's such a tight turn, motorists are advised by warning signs to slow down to 35 MPH.