In 2003, the Seattle terminus was re-engineered to better accommodate traffic from the two nearby sports stadiums. I-90 westbound still ends at its previous location next to Qwest Field, but eastbound begins about 1/4 mile (0.4 km) south at Edgar Mart®™nez Drive near the roof shed of Safeco Field at an interchange with 4th Avenue S.
The tunnel that carries Interstate 90 under the Mount Baker Ridge is on the National Register of Historic Places. The east portal of the tunnel (visible when entering Seattle from the east) is constructed as a bas relief concrete sculpture.
Interstate 90 at the Vantage BridgeI-90 incorporates two of the longest floating bridges in the world, the Lacey V. Murrow Memorial Bridge and the Homer M. Hadley Memorial Bridge, which cross Lake Washington from Seattle to Mercer Island, Washington. They are the second and fifth longest such bridges, respectively.
Forty miles east of Bellevue I-90 traverses the Cascade Range's Snoqualmie Pass, elevation 3,022 feet. At mile 137, it crosses the Columbia River on the Vantage Bridge, and after entering Spokane near mile 279, enters Idaho 20 miles later.
Since 1980, I-90 from Seattle to Thorp, WA, was designated the Mountains To Sound Greenway to protect its outstanding scenic and cultural resources.
The small town of Wallace, Idaho still prides itself on having what was the last stop light on I-90. Its downtown has many historical buildings, which would have been wiped out by the original planned route of the freeway, so in 1976, city leaders had the downtown placed on the National Register of Historic Places. As a result, the federal government was forced at great expense to reroute the freeway to the northern edge of downtown and elevate it. That section of I-90 opened in September 1991. A bicycle path is routed beneath part of that segment.
Until 1995 in Montana near the Idaho border, I-90 was not a divided highway for a few stretches, having only a narrow paved median. From 1995 until 1999, the speed limit in Montana was "reasonable and prudent"; it is now 75 mph (120 km/h). On the I-90, at Exit 00 (right on the MT/ID border) is the Lookout Pass Ski Area, and one exit east of there is the Hiawatha Trail (rails-to-trails).
At the Montana border I-90 is a four-lane divided highway with a grass median. At Buffalo, Wyoming (if travelling eastward from the north) it diverges from I-25 with a more east-west orientation.
The South Dakota section of I-90 is defined at South Dakota Codified Laws 31-4-184.
Near Sturgis, South Dakota at the Wyoming border I-90 is a four lane divided highway with a grass median. In the Sioux Falls area, I-90 intersects I-29 and continues east a short distance to Minnesota. I-90 is the largest east-west thoroughfare in South Dakota.
The Minnesota section of I-90 is defined as Route 391 in Minnesota Statutes 161.12(3).
I-90 crosses southern Minnesota from the South Dakota border near Sioux Falls to the Mississippi River near La Crosse, Wisconsin. On most of its length in the state, it is close to the Iowa border and fairly parallel with it. In southeast Minnesota, it curves north to Rochester.
I-90 crosses Wisconsin from Minnesota to Illinois in a generally southeasterly direction. It joins I-94 in Tomah and I-39 in Portage. I-94 separates from I-90 at Madison.
I-39/90/94 from just south of Portage to Madison is the longest concurrency of three interstate highways in the United States.
In the state of Illinois, Interstate 90 enters Illinois north of Rockford oriented north-south joined with Interstate 39. It then runs east-southeast directly to the city of Chicago. From Rockford to Interstate 294 the road is tolled and called the Northwest Tollway. In 2007, the Illinois State Toll Highway Authority renamed the Northwest Tollway, the Jane Adams Memorial Tollway. In Chicagoland, I-90 is known by three names from O'Hare International Airport to the Indiana state line. The Kennedy Expressway runs from O'Hare to Interstate 290 and the Chicago Loop. I-90 continues running south of the Loop on part of the Dan Ryan Expressway, and then southeast onto the tolled Chicago Skyway into Indiana.
In the state of Indiana, Interstate 90 runs over the Indiana Toll Road. Interstate 90 enters from Illinois at the Chicago Skyway. It then runs to the concurrency of Interstates 80/94 east of Interstate 65, where I-80 leaves I-94 and joins with I-90. The combined I-80/90 route runs east across northern Indiana and near the southern border of Michigan to the Ohio state line.
As part of the Toll Road, I-80/90 passes to the north of South Bend and Elkhart. It also passes north of Angola at Interstate 69.
The Indiana Toll Road turns into the Ohio Turnpike as it crosses the border. I-90 follows the Ohio Turnpike until Lorain (west of Cleveland), where it turns north to follow a route near the shores of Lake Erie.
In Cleveland, Interstate 90 serves as the Innerbelt at the confluence of the northern termini of Interstates 71 and 77. One of the most peculiar and hazardous stretches of Interstate 90 is the section of highway passing through downtown, known locally as Dead Man's Curve. Here, the road takes a nearly 90-degree turn. While there are plenty of large signs and flashing lights alerting motorists to this turn, there have still been a large number of accidents due to inattentive motorists. There are plans to realign the freeway along a shallower curve within the next decade, as part of a larger project to improve the highway system in Cleveland.
I-90 goes from the Ohio state line through Erie, Pennsylvania, and then leaves Pennsylvania for New York.
While not an interstate, a portion of Pennsylvania Route 5 in Erie has recently been named Pennsylvania Route 290. The purpose is to encourage travelers to use this stretch of Erie's 12th Street as a loop, connecting Interstate 79 and 90 to the Bayfront Connector and downtown Erie.
I-90 becomes the New York State Thruway upon entering New York. It follows the Lake Erie coast until Buffalo, where it joins the old Water Level Route until Albany. There, it takes a short detour before joining the New York State Thruway Berkshire Connector.
I-90 metric sign for NY Thruway Exit 35Almost all of the New York portion of the road is a toll road, comprising the east-west portion of the New York State Thruway mainline and part of the Berkshire Connector, operated by the New York State Thruway Authority. It was originally constructed as part of the Thruway project in the middle 1950s and received its current designation as Interstate 90 in 1958. I-90 (operated by NYSDOT) carries Interstate 90 between the two; however, the Berkshire Section directly connects to the mainline (at Thruway interchange 21A) 6.5 miles (10.5 km) west of the point where I-90 joins it (at Thruway interchange B1).
The mileposts and exit numbers on the New York State Thruway mainline originate at the New York City line and increase northward along Interstate 87 and westward along Interstate 90. As a result, mileposts and exit numbers on the I-90 section of the Thruway mainline increase from east to west, contrary to modern practices where numbers increase from the west or south. The NYSDOT-maintained portion in between, known to locals as "Freebie 90," does number its mileage and exits in the traditional west-to-east method. (Ironically, "Freebie 90" is oriented geographically north-south for most of its length, so the exit numbers seem to increase from north to south.) Exit and milepost numbering starts over again when the Berkshire Section of the Thruway begins, with exit and mile numbers preceded by the letter B (Exit B1, Exit B2, Mile B1, Mile B2, and so on).
There once were two metric-only signs on the westbound New York State Thruway around Syracuse, which is about 100 miles (161 km) from Canada. The NYS Thruway Authority decided to test metric signage, which may have briefly included an 88 km/h speed limit sign, on the Thruway. There was also a sign displaying the distance to the Interstate 81 interchange in kilometers in Dewitt. These signs are now displayed in just miles.
I-90 is the only Interstate having a complete set of nine spur routes (190, 290, 390...890, 990) within one state, which is in New York. (Interstate 80 has a complete set in different states.) In addition, I-990, a short spur route near Buffalo, New York not directly connected to I-90, is the highest number given to an Interstate.
I-790 in Utica used to have a completely direct connection with the I-90 at Thruway interchange 31. Various road redesign projects over the years have eventually led to this direct connection being partially severed. Traffic exiting the Thruway must use two different surface streets to reach I-790. However, it is still possible to travel from I-790 directly onto the Thruway. I-790 has some other oddities: no exit numbers, no reassurance markers, and it runs concurrent with New York State Route 5 for its entire length.
The New York section of I-90 west of the Berkshire section of the New York Thruway is defined as Interstate Route 504 in New York Highway Law °ž 340-a.
I-90 in Massachusetts runs along the pre-Interstate era Massachusetts Turnpike which opened on May 15, 1957 from West Stockbridge at the New York state border to Massachusetts Route 128.
The "Boston Extension" opened in September of 1964 from the original terminus at Route 128 to the Allston/Brighton Tolls
The full Boston Extension opened on February 18, 1965 continuing from the Allston/Brighton Tolls to I-93 in Downtown Boston. The new extension added 12 miles to the MassPike's original 123.
I-90 was extended again as part of the Big Dig from its terminus at I-93 to Boston's Logan International Airport and a terminus of Route 1A in January 2003 via tunnels under the Fort Point Channel and the Ted Williams Tunnel under Boston Harbor. This extended I-90 by an additional 1.3 miles (2.1 km), shifting the eastern terminus to Route 1A.
Turnpike Doubles are permitted to travel between exit 11 and through the New York state border.