Interstate 90

Interstate 90 (I-90) is the longest Interstate Highway in the United States, extending 3,021 miles (4,862 km) from its western terminus at Seattle, Washington, to its eastern terminus at Boston, Massachusetts.^[1][2] As part of the Dwight D. Eisenhower National System of Interstate and Defense Highways, it serves as a primary east-west transcontinental corridor, crossing 13 states and connecting major urban centers while facilitating freight and passenger travel across diverse landscapes from the Pacific Northwest to the Atlantic Seaboard.^[1][3] The route begins in Washington, where it covers 297 miles through mountainous terrain and urban areas, including a crossing of the Cascade Mountains via Snoqualmie Pass, before entering Idaho for 74 miles.^[4] It then proceeds through Montana (551 miles), Wyoming (208 miles), and South Dakota (413 miles), traversing the Northern Rockies, Great Plains, and Badlands, with key cities such as Billings, Montana, and Sioux Falls, South Dakota.^[4][1][5] Continuing eastward, I-90 spans Minnesota (275 miles), Wisconsin (188 miles), and Illinois (107 miles), passing through Minneapolis–Saint Paul and Chicago, where it briefly overlaps with I-94 and I-294 in the Chicago metropolitan area.^[4][1] In the Midwest and Northeast, the highway covers Indiana (157 miles), Ohio (244 miles), Pennsylvania (47 miles), New York (385 miles), and Massachusetts (138 miles), linking cities like Cleveland, Ohio; Buffalo, New York; and Albany, New York, before concluding in the Boston area via the Massachusetts Turnpike.^[4][1] I-90 is renowned for its engineering feats, including long bridges like the Vantage Bridge over the Columbia River in Washington and extensive toll sections, such as the New York State Thruway and the Indiana Toll Road, which help fund maintenance and operations.^[3] The highway supports high volumes of traffic, with segments near Chicago experiencing over 200,000 vehicles daily, underscoring its role in national commerce and connectivity.

Route description

Washington

Interstate 90 begins at its western terminus in Seattle at the junction with State Route 519 near the Port of Seattle.^[6] From there, the route heads eastward through urban Seattle, passing under the Mount Baker neighborhood via the Mount Baker Ridge Tunnel, a pair of bores carrying the mainline and reversible express lanes.^[7] It then crosses Lake Washington on a pair of parallel floating bridges: the eastbound Lacey V. Murrow Memorial Bridge, the world's longest floating bridge at 7,578 feet including approaches, and the westbound Homer M. Hadley Memorial Bridge.^[8] These structures connect Seattle to Mercer Island and continue into Bellevue, forming a critical east-west corridor for commuters and freight in the Puget Sound region.^[9] East of Bellevue, I-90 ascends into the Cascade Range, reaching Snoqualmie Pass at an elevation of 3,022 feet, the lowest major east-west crossing through the mountains.^[10] The pass features protective infrastructure including snowsheds, avalanche bridges spanning chutes, and gates for avalanche control to mitigate winter hazards along this high-traffic route averaging over 34,000 vehicles daily.^[11] Beyond the pass, the highway descends into rural Kittitas County, passing through Ellensburg, a hub for agriculture and education, before traversing the arid Columbia Basin. It continues through Moses Lake, serving irrigation-dependent farmlands, and reaches the Idaho state line near Spokane after 297.5 miles in Washington, with the eastern segment linking to the Spokane metropolitan area.^[12][13] Traffic volumes on I-90 vary significantly, peaking at up to 250,000 vehicles per day near Seattle's urban core where congestion is routine, and dropping to around 20,000 vehicles per day in the rural eastern sections.^[14] A unique aspect of the route's western segment is its integration with Sound Transit's 2 Line light rail extension, which shares infrastructure including the Mount Baker Tunnel and I-90 corridor, with testing underway and full service planned to open in early 2026 to enhance multimodal connectivity across Lake Washington.^[15][16]

Idaho

Interstate 90 enters Idaho from Washington just east of the Spokane metropolitan area, crossing the state line near the community of Hauser Lake before reaching Post Falls in Kootenai County.^[17] The freeway then proceeds eastward through the northern Idaho panhandle, a narrow region characterized by its rural landscapes and proximity to the Canadian border. Shortly after entering the state, I-90 intersects with U.S. Route 95 in Coeur d'Alene, providing access to the region's primary north-south corridor.^[18] In Coeur d'Alene, the largest city in northern Idaho, I-90 passes near the southern edge of the urban area, offering views of the city's downtown and the expansive Coeur d'Alene Lake to the south. The route follows the north shore of the lake for several miles, traversing a mix of developed shorefront and preserved natural areas that highlight the panhandle's recreational appeal. Key landmarks along this stretch include Tubbs Hill, a prominent 120-acre forested peninsula jutting into the lake, which provides scenic overlooks accessible via local roads near exit 11.^[18] The freeway's alignment here emphasizes the lake's beauty, with opportunities for travelers to exit and explore waterfront parks and trails. East of Coeur d'Alene, I-90 winds through increasingly rural and forested terrain, ascending into the Bitterroot Range's foothills and the historic Silver Valley mining district in Shoshone County. This section parallels the South Fork of the Coeur d'Alene River, passing small communities like Huetter, Rathdrum, and Dalton Gardens before entering the mountainous Silver Valley, known for its legacy of silver mining centered around towns such as Kellogg, Smelterville, and Wallace. The route navigates tight curves and steep grades amid dense conifer forests, reflecting the challenging topography of the Idaho Panhandle. In 2025, the Idaho Transportation Department is undertaking improvements in the Kellogg area, including bridge replacements over I-90 to enhance safety and reduce maintenance needs.^[19] Further east, the freeway approaches the Montana state line at Lookout Pass, elevation 4,720 feet, after traversing the rugged Lookout Pass area. Spanning approximately 74 miles across Kootenai and Shoshone counties, I-90's traversal of Idaho is the shortest of any state along its path, characterized by low to moderate traffic volumes that range from about 5,000 vehicles per day in the remote eastern Silver Valley segments to over 30,000 near Coeur d'Alene.^[17][20] This relatively light usage contributes to its appeal as a scenic drive, with portions adjacent to designated byways like the White Pine Scenic Byway near Cataldo, offering glimpses of historic mining sites and natural features. Travelers can access Old Mission State Park, the oldest building in Idaho and a National Historic Landmark from 1853, just south of exit 39 near Cataldo, providing insight into the region's Jesuit missionary history.^[21] Overall, I-90 in Idaho serves as a gateway to the panhandle's blend of outdoor recreation, cultural heritage, and untamed wilderness.

Montana

Interstate 90 enters Montana from Idaho at Lookout Pass in the Bitterroot Mountains at an elevation of approximately 4,710 feet, marking the start of its 552-mile traverse through the state—the longest portion of the highway in any single state. The route initially descends eastward through forested mountainous terrain in Mineral and Missoula counties, passing near the city of Missoula, a regional hub with universities and outdoor recreation areas. Continuing east, I-90 climbs into the Rocky Mountains, navigating the Clark Fork Valley and paralleling the Clark Fork River before reaching Butte in Silver Bow County, where it briefly overlaps with Interstate 15 for about 7.5 miles. This western section features steep grades and curves, with the highway crossing the Continental Divide at Homestake Pass near Butte at an elevation of 6,329 feet, the highest point along the entire I-90 corridor.^[22][22][22] East of Butte, I-90 transitions from the Rockies into rolling plains and grasslands, passing through Whitehall, Three Forks, and Bozeman in Gallatin County before entering the Paradise Valley along the Yellowstone River. The highway serves Bozeman, a growing city near Montana State University, and continues to Livingston, Columbus, and Laurel, culminating in Billings, the state's largest city and a major commercial center with over 110,000 residents. From Billings, I-90 proceeds southeast through the Crow Indian Reservation near Hardin, crossing the Yellowstone River multiple times, before descending into high plains and exiting to Wyoming south of the community of Ashland in Big Horn County. Throughout this eastern expanse, the route integrates with the landscape via wide medians and rural design elements to accommodate the open terrain.^[22][22][22] Much of I-90 in Montana maintains a predominantly rural character, with daily traffic volumes ranging from about 5,000 vehicles in remote mountain and plains sections to peaks exceeding 47,000 near Billings, where it handles the highest annual average daily traffic (AADT) of 47,960 as of 2023. The highway often parallels BNSF Railway lines, particularly north of the route through the Billings area and along the Yellowstone Valley, facilitating freight transport alongside interstate travel. Its proximity to Yellowstone National Park—accessible via U.S. Route 191 from Bozeman—draws tourists, while ongoing studies address wildlife connectivity, including potential overpasses and underpasses near Missoula to mitigate animal-vehicle collisions in habitat-rich areas like the Sixmile Creek region.^[23][24][25]

Wyoming

Interstate 90 enters Wyoming from Montana near Parkman in Sheridan County, running concurrently with U.S. Highway 87 southward through rolling grasslands and low hills toward the city of Sheridan. The route spans 208 miles across the northeastern corner of the state, primarily through sparsely populated rural areas characterized by high plains terrain south of the Bighorn Mountains. In Sheridan, I-90 serves as a key transportation link, with interchanges providing access to local roads and business routes before continuing southeast past the historic Fort Phil Kearny State Historic Site near exit 44.^[26][27] From Sheridan, the highway proceeds east to Buffalo, where it briefly intersects Interstate 25 at a tri-level interchange, offering connectivity to southern Wyoming routes. Beyond Buffalo, I-90 traverses the Powder River Basin, a major energy-producing region rich in oil and coal resources, with the freeway facilitating transport for these industries through its alignment across active extraction fields. The route passes through Gillette, a hub for mining operations, before continuing northeast to Sundance and exiting the state toward South Dakota near Aladdin.^[28][26] The terrain along I-90 in Wyoming features broad, open plains with gradual undulations, maintaining elevations generally between 3,500 and 4,500 feet above sea level, providing a relatively flat driving experience compared to more mountainous interstate segments. Rural conditions dominate, with frequent wildlife crossings for pronghorn antelope and limited services such as fuel and rest areas between major towns like Sheridan, Buffalo, and Gillette, emphasizing the route's role in connecting isolated communities.^[29][30] Daily traffic volumes remain low throughout the Wyoming segment, with annual average daily traffic (AADT) ranging from approximately 1,700 vehicles near remote interchanges to over 16,000 in urban approaches like Sheridan and Gillette, reflecting the area's low population density and regional travel patterns.^[31]

South Dakota

Interstate 90 enters South Dakota from Wyoming in Lawrence County near Spearfish as a four-lane divided highway concurrent with U.S. Highway 14, marking the beginning of its 412.8-mile traversal across the state to the Minnesota border. The route initially winds through the northern Black Hills region, briefly overlapping with U.S. Highway 85 near Sturgis before reaching Rapid City, the state's second-largest city and a gateway to attractions like Mount Rushmore National Memorial, accessible via U.S. Highway 16 from exit 61. Beyond Rapid City, I-90 skirts the southern edge of the Black Hills National Forest, passing Box Elder and Ellsworth Air Force Base, while providing connections to scenic byways that highlight the area's forested hills and granite formations.^[32][33][34] East of the Black Hills, the freeway transitions into the rugged terrain of the Badlands, running parallel to the northern boundary of Badlands National Park between exits 110 and 131, where drivers can access South Dakota Highway 240 for the park's scenic loop road featuring overlooks like Pinnacles Overlook and Yellow Mounds Overlook that showcase eroded buttes, spires, and layered sedimentary rock. The route crosses the Missouri River at Chamberlain via a modern bridge, after which it enters the flatter eastern prairies characterized by vast agricultural fields and rolling grasslands, passing through towns like Mitchell and Sioux Falls before exiting the state near Brandon. This eastern segment contrasts sharply with the western topography, offering expansive views of the Great Plains.^[35][36][37] Traffic on I-90 in South Dakota varies by location, with average annual daily traffic (AADT) ranging from approximately 10,000 vehicles per day in rural western sections near the Black Hills to 40,000 or more near Sioux Falls, reflecting its role as a key east-west corridor for freight and tourism. Near Sioux Falls, ongoing infrastructure improvements include the 2025 reconstruction of the eastbound lanes and associated structures at exit 406 in Brandon, enhancing safety and capacity for high-volume traffic. Unique features along the route include several rest areas with thematic exhibits, such as the South Dakota Dinosaur Park near Chamberlain at mile marker 263, which displays life-size replica dinosaurs and fossil exhibits to educate visitors on prehistoric life in the region. Additionally, the iconic Wall Drug Store, located just off exit 110 in Wall, draws travelers with its roadside advertising and proximity to the Badlands entrance, serving as a major stop for refreshments and souvenirs.^{[38][39][40][41][42]}

Minnesota

Interstate 90 enters Minnesota from South Dakota at the state line west of Beaver Creek, approximately 15 miles east of Sioux Falls, and extends 275 miles eastward to the Wisconsin border near La Crescent. The highway traverses the southern edge of the state, passing through rural communities and key cities such as Luverne, Worthington, Fairmont, Albert Lea, Austin, Rochester, and Winona. Rochester stands out as a prominent medical center, anchored by the Mayo Clinic, which draws significant regional traffic to the corridor. Near Albert Lea, I-90 briefly intersects Interstate 35, facilitating connections northward. The route primarily crosses flat to gently rolling agricultural landscapes of the Minnesota prairie, dominated by vast farmlands dedicated to corn, soybeans, and livestock production, with no major mountain ranges or significant elevation changes. In its southeastern segment, the highway approaches the scenic Root River valley within the Driftless Area, characterized by wooded bluffs, riverine terrain, and karst features that add subtle topographic variety without impeding travel. This predominantly rural path supports local farm service routes, enabling efficient access to agricultural operations and markets while avoiding urban congestion. Traffic volumes on I-90 in Minnesota typically range from 20,000 to 55,000 vehicles per day, with higher counts near population centers like Rochester and lower figures in remote western sections. A distinctive feature along the route is the "Golden Stripe" near Blue Earth, a gold-tinted concrete stripe spanning all lanes that commemorates the 1978 completion of I-90's construction in the state, symbolizing the east-west segments' convergence similar to the transcontinental railroad's golden spike. The highway's southern alignment effectively bypasses the Minneapolis-Saint Paul metropolitan area, streamlining cross-country travel through the region's agricultural heartland.

Wisconsin

Interstate 90 enters Wisconsin from Minnesota at the Mississippi River near La Crosse and extends eastward for 187 miles through the southern part of the state to the Illinois border near Beloit. The route initially follows a rural path through the western counties, passing Tomah and the Wisconsin Dells before reaching the Madison metropolitan area and continuing via Janesville.^[43][44] In its western segment, I-90 traverses the Driftless Area, a region of unglaciated terrain featuring steep coulees, rolling hills, and deep valleys formed by stream erosion rather than glacial activity.^[45] The highway crosses the Wisconsin River near Portage, where it joins concurrent routes including I-94 from Tomah to Madison and I-39 from Portage southward. Near the state capital of Madison, the freeway shifts to a more urban environment, with an overlap along US 151 that serves as a partial bypass for local traffic around the city.^[44] Traffic volumes along I-90 in Wisconsin typically range from 30,000 to 80,000 vehicles per day, with higher concentrations near Madison due to its role as a regional hub.^[46] The route offers scenic views of Lake Wisconsin, a reservoir on the Wisconsin River between Sauk and Columbia counties, and integrates closely with the state's park system, providing easy access to areas like Mirror Lake State Park near the Dells.^[47][44]

Illinois

Interstate 90 enters Illinois from Wisconsin near South Beloit, initiating its 123.89-mile (199.38 km) traverse through the northern part of the state, primarily serving as a key corridor for freight and commuter traffic in the Chicago metropolitan region. The highway quickly reaches Rockford, a mid-sized city where it functions as a major east-west artery amid suburban and light industrial development. From the state line, I-90 is routed along the Jane Addams Memorial Tollway, a 76-mile tolled expressway maintained by the Illinois State Toll Highway Authority, which facilitates efficient travel through rolling farmland and growing exurbs before approaching the denser urban fringe west of Chicago.^[48][49] As I-90 nears Chicago, it intersects the O'Hare International Airport area, where it briefly overlaps with I-190 before continuing eastward as the Kennedy Expressway, cosigned with I-94. This segment crosses directly over the airport's runways and terminals, supporting high volumes of airport-related traffic amid one of the nation's busiest aviation hubs. The Kennedy Expressway carries more than 275,000 vehicles daily in its core sections, reflecting intense urban demand, and features a reversible express lane system to manage peak-hour flows. In the 2020s, the Illinois Department of Transportation completed a $169 million rehabilitation of 36 bridges along the Kennedy, enhancing structural integrity and reducing maintenance needs without expanding capacity.^[50][51] Southeast of downtown Chicago, I-90 diverges from I-94 at the Jane Byrne Interchange and overlaps with I-94 again along the Dan Ryan Expressway, navigating through densely packed industrial corridors, rail yards, and residential neighborhoods on the city's South Side. This urban stretch contends with some of the heaviest traffic in Illinois, exceeding 300,000 vehicles per day near key interchanges, underscoring I-90's critical role in regional logistics. The route culminates at the Chicago Skyway, a 7.8-mile elevated toll bridge that rises above industrial zones and the Calumet River, providing a tolled bypass to the Indiana state line and linking seamlessly to the Indiana Toll Road.^[52][53] Throughout Illinois, I-90 exemplifies a transition from semi-rural tollway to high-density urban freeway, bordered by manufacturing facilities, warehouses, and commercial districts that amplify its economic significance while contributing to persistent congestion challenges in the Chicago core.^[54]

Indiana

Interstate 90 enters northeastern Indiana from Illinois near Hammond, forming the entirety of the 157-mile Indiana Toll Road, a controlled-access toll highway that extends eastward to the Ohio state line.^[55] The route parallels the southern shore of Lake Michigan, traversing seven counties: Lake, Porter, LaPorte, St. Joseph, Elkhart, LaGrange, and Steuben.^[56] As a key segment of the transcontinental Interstate 90, it serves as a vital corridor for freight and passenger traffic, with average daily volumes ranging from 50,000 to 100,000 vehicles, peaking near urban centers in the west.^[57] In its western portion, I-90 cuts through the heavily industrialized Calumet region, passing Gary's prominent steel mills, including the massive U.S. Steel Gary Works facility along the lakeshore.^[58] The highway offers views of the industrial landscape, including railyards and factories, while the nearby Cline Avenue (State Road 912) provides a tolled bridge connection over the Indiana Harbor and Ship Canal to access mills and refineries in East Chicago and Gary.^[59] This section highlights contrasts in the local environment, with areas of urban decay amid abandoned structures and ongoing industrial activity in Gary, before transitioning eastward through suburban Portage and the Indiana Dunes area.^[60] Further east, the toll road passes through the more residential and commercial zones of Chesterton and LaPorte, then reaches South Bend, where Exit 77 provides direct access to the University of Notre Dame via U.S. Route 31 and State Road 933.^[61] Beyond South Bend, I-90 continues past Mishawaka and the recreational areas around the St. Joseph River, entering Elkhart County's Amish-influenced farmlands. In its eastern reaches, the highway shifts to predominantly rural scenery, winding through wooded and agricultural lands in LaGrange and Steuben counties, with interchanges serving smaller communities like Howe and Angola before crossing into Ohio near mile marker 157.^[56] This rural contrast to the urban west underscores the route's diverse passage across Indiana's northern tier.

Ohio

Interstate 90 enters Ohio from Indiana near Toledo, spanning 244.8 miles across the northern part of the state before exiting into Pennsylvania.^[62] For much of its length, I-90 parallels the Ohio Turnpike, a tolled freeway operated by the Ohio Turnpike Commission, which it overlaps from the Indiana state line eastward through cities including Toledo, Elyria, Akron, and Cleveland.^[63] The route provides a major east-west corridor, facilitating travel along the southern shore of Lake Erie and connecting industrial and urban centers in the region.^[64] As I-90 progresses eastward, it skirts the southern edge of Lake Erie, offering scenic views of the lake while navigating dense urban environments, particularly in the Cleveland metropolitan area. In Cleveland, the highway passes near key landmarks such as the Rock and Roll Hall of Fame, accessible via Exit 174B onto Ohio State Route 2 (Cleveland Memorial Shoreway).^[65] The segment through Cleveland features elevated viaducts and interchanges that integrate with the city's downtown infrastructure, handling heavy commuter and tourist traffic along the waterfront.^[66] In the 2020s, the Ohio Department of Transportation (ODOT) has undertaken significant reconstruction efforts on I-90, including a major project adding a third lane in each direction from the SR 2 interchange to SR 611 near Elyria, spanning approximately eight miles from the Ohio Turnpike toll booth.^[67] This work aims to improve capacity and safety on the aging infrastructure, with pavement replacement and bridge upgrades ongoing through 2028.^[68] Additionally, rehabilitation of the Inner Belt Bridge in Cleveland, part of the broader Innerbelt Modernization Plan, continues to address structural deficiencies on the I-90 viaduct over the Cuyahoga River, with phases extending into 2027.^[69] Traffic volumes on I-90 in Ohio vary widely, ranging from about 40,000 vehicles per day in rural segments to over 120,000 in urban areas like Cleveland, reflecting its role as a vital freight and passenger artery.^[70] The Ohio Turnpike features service plazas every 30 to 50 miles, providing 24-hour amenities such as fuel stations, restaurants, restrooms, and pet areas to support long-distance travelers.^[71] These facilities, including locations like the Vermilion Valley and Portage plazas, enhance safety and convenience along the tolled portion of the route.^[63]

Pennsylvania

Interstate 90 traverses 46 miles (74 km) entirely within Erie County in northwestern Pennsylvania, entering from Ohio west of North East and exiting into New York east of Erie. The route begins at the state line near the village of North East, proceeding eastward through predominantly rural landscapes while paralleling the southern shore of Lake Erie for much of its length. It offers scenic views of the lake and provides access to Presque Isle State Park—a 3,112-acre (1,259 ha) peninsula state park—via Exit 18 at Peninsula Drive, allowing travelers to reach beaches, trails, and recreational areas.^[72] As I-90 approaches the city of Erie, it transitions briefly into urban surroundings, serving as a key connector in the region's transportation network. In Erie, the highway intersects Interstate 86 (the southern leg of the New York State Thruway system) at Exit 37 and Interstate 79 at Exits 22A-B, facilitating travel to downtown Erie and surrounding suburbs.^[73] East of the city, the route reenters rural terrain, passing through townships like Harborcreek before reaching the New York border near Ripley. This segment stands out as toll-free, providing relief for eastbound drivers after the tolled Ohio Turnpike to the west.^[74] Daily traffic on I-90 in Pennsylvania remains moderate, with an average annual average daily traffic (AADT) of 27,395 vehicles across the route in 2023, ranging from 20,000 to 40,000 vehicles per day depending on location—lower in rural stretches and higher near Erie.^[75] To maintain the highway's condition, the Pennsylvania Department of Transportation (PennDOT) initiated a multiyear reconstruction program in the late 2010s, targeting approximately 28 miles over a decade through various contracts. A notable component was the $37.6 million project launched in 2019, which included replacing bridges like the Huntley Road overpass to enhance clearance, safety, and pavement smoothness in Erie County.

New York

Interstate 90 enters New York from Pennsylvania at the state line near the town of Ripley in Chautauqua County, marking the beginning of its 385.48-mile journey across the state as the tolled New York State Thruway mainline.^[76] The highway proceeds northeast along the southern shore of Lake Erie through rural western New York before reaching the urban core of Buffalo, where it provides access to the nearby Niagara Falls via the connecting I-190 spur.^[77] From Buffalo, I-90 turns eastward, passing through the cities of Rochester, Syracuse, and Albany, while traversing a mix of suburban, urban, and rural landscapes; it ultimately exits the state into Massachusetts near Canaan in Columbia County, after briefly skirting the northern edges of the Hudson Valley region.^[78] Near Albany, I-90 intersects with I-87, the Northway, facilitating connections southward along the Hudson River corridor.^[79] As a toll road managed by the New York State Thruway Authority, I-90 features barrier tolling systems and service areas along its length, with the route roughly paralleling the historic Erie Canal from Buffalo to Albany, reflecting the waterway's influence on the state's east-west transportation axis.^[80][81] The western sections near Ripley and through Chautauqua County remain predominantly rural, characterized by agricultural lands and sparse development, while the corridor becomes increasingly urban around Buffalo, where it navigates dense commercial and residential areas proximate to Niagara Falls.^[82] Further east, the highway alternates between suburban stretches near Rochester and Syracuse and more open countryside, before entering the Capital District around Albany. A key feature is the Castleton-on-Hudson Bridge, a cantilever truss structure that carries I-90 across the Hudson River between Rensselaer and Albany counties, providing a vital link in the route's path.^[83] Traffic volumes on I-90 in New York vary significantly by section, with average annual daily traffic (AADT) ranging from approximately 50,000 vehicles per day in rural western areas to over 150,000 in urban zones near Syracuse and Albany, according to New York State Department of Transportation data.^[84] The highway serves as a critical artery for both passenger and freight movement, supporting regional connectivity amid ongoing infrastructure maintenance, such as recent rehabilitation projects on the Castleton-on-Hudson Bridge.^[85] The communities along I-90's path, particularly in Upstate New York cities like Buffalo, Rochester, and Syracuse, have experienced significant de-industrialization since the mid-20th century, leading to economic challenges including population decline and manufacturing job losses.^[86] Revitalization efforts, such as the state's Upstate Revitalization Initiative launched in 2015, have focused on these corridor areas to foster job creation, infrastructure improvements, and downtown redevelopment, aiming to leverage the highway's role in regional economic recovery.^[87]

Massachusetts

Interstate 90 enters Massachusetts from New York near the town of Canaan, crossing the state line in West Stockbridge and spanning a total of 138 miles eastward to its national eastern terminus at Massachusetts Route 1A (Emerson Street) in East Boston, adjacent to Logan International Airport.^[88] The route traverses diverse terrain, beginning in the Berkshire Mountains, passing through major cities including Springfield, Worcester, and Framingham, before reaching the densely populated Boston metropolitan area.^[88] Throughout its length, I-90 serves as the primary east-west corridor in the state, facilitating travel between western Massachusetts and the Atlantic coast.^[89] Designated as the Massachusetts Turnpike (commonly called the Mass Pike), I-90 is a controlled-access toll road for nearly its entire extent in the state, with tolls collected electronically via E-ZPass or Pay By Plate systems.^[90] The turnpike features multiple lanes and serves high volumes of both local and long-distance traffic, with average annual daily traffic (AADT) ranging from approximately 80,000 vehicles near Springfield to over 130,000 in the Boston metro area east of the Allston interchange.^[91][92] In the urban core, the route incorporates extensions completed as part of the Central Artery/Tunnel Project (Big Dig), routing traffic through the Ted Williams Tunnel beneath Boston Harbor to connect downtown Boston with Logan Airport.^[89] This underwater segment, spanning 1.6 miles, provides a direct link for eastbound I-90 travelers, enhancing access to the airport and reducing surface travel through the city.^[89] A brief overlap with Interstate 95 occurs near Weston, where the two routes share alignment for about 1.5 miles before I-90 continues independently toward Boston.^[88] Ongoing infrastructure enhancements include the Allston Multimodal Project, which aims to reconfigure the I-90 interchange in Boston's Allston neighborhood to improve traffic flow, add multimodal connections, and depress the turnpike viaduct for better urban integration; construction is phased and expected to continue through the late 2020s.^[92] These improvements address congestion at a key bottleneck handling significant commuter and freight traffic.^[92]

History

Pre-interstate highways and planning

The roots of Interstate 90 trace back to the early 20th-century auto trail movement, which sought to establish marked transcontinental routes for automobiles amid the growing popularity of motor travel. The Yellowstone Trail, organized in 1912 as the first coast-to-coast automobile highway, followed a northern path from Plymouth Rock in Massachusetts to Puget Sound in Washington, passing through key cities and natural landmarks that later aligned with I-90's corridor.^[93] Similarly, the Black and Yellow Trail, developed around 1913, connected Chicago to Yellowstone National Park via South Dakota and Wyoming, forming a foundational segment in the Midwest and Great Plains that influenced subsequent highway alignments.^[94] These named trails, often improved through local and state efforts, addressed the lack of standardized long-distance roads and laid the conceptual groundwork for a unified national network. Federal planning for a modern interstate system gained momentum during World War II, with the Federal-Aid Highway Act of 1944 authorizing the designation of a 40,000-mile National System of Interstate Highways to include transcontinental routes, among them a northern east-west corridor from Boston to Seattle.^[95] This legislation built on the 1944 Interregional Highways report, which advocated for limited-access superhighways to link major urban centers and facilitate interstate commerce and defense mobility along such paths.^[96] By 1955, the Bureau of Public Roads released the General Location of National System of Interstate Highways—informally called the Yellow Book—which detailed proposed alignments for this northern route, emphasizing high-capacity freeways to bypass congested areas while connecting population centers from Massachusetts through the Midwest to Washington state. Anticipating federal involvement, several states independently developed toll roads in the early 1950s that would later integrate into I-90. In Ohio, the Ohio Turnpike Commission was established in 1949 to build a 241-mile limited-access highway across the northern part of the state; construction began in 1952, and the full route opened to traffic on October 1, 1955, just before the Interstate system's formal launch.^[97] New York authorized the New York State Thruway in 1950 as a 496-mile toll system spanning the state; initial segments, including those along the future I-90 path, opened in 1954, providing a model for high-speed, divided roadways. Massachusetts formed the Massachusetts Turnpike Authority in 1952 to construct a 123-mile toll road from the New York border to near Boston; ground was broken in January 1955, with western sections completed by 1957 to link into the national framework.^[98] Planning for the northern interstate route faced significant challenges, particularly debates over rural versus urban alignments and local opposition in key cities. Proponents favored rural bypasses to minimize costs and disruption, but urban interests pushed for direct city connections to boost economic access, leading to contentious route selections in the Midwest and Northeast. In Seattle, early proposals for I-90 encountered resistance from residents and officials over extensive right-of-way acquisitions that threatened neighborhoods and parkland, prompting design modifications to reduce urban impacts.^[99] Boston saw similar urban opposition, with concerns about the Massachusetts Turnpike's approach disrupting historic districts and low-income communities, fueling broader discussions on balancing regional connectivity with local preservation.^[99] These debates highlighted tensions between national efficiency goals and community concerns, shaping the final alignments through compromises like elevated sections and interchanges.^[100]

Establishment and early construction

The Interstate Highway System, including Interstate 90 (I-90), was authorized by the Federal-Aid Highway Act of 1956, signed into law by President Dwight D. Eisenhower on June 29, 1956, which established a 41,000-mile network of controlled-access highways to enhance national defense and commerce.^[101] I-90, envisioned as the longest east-west transcontinental route spanning from Seattle, Washington, to Boston, Massachusetts, received its official numbering and route designation in August 1957 by the American Association of State Highway Officials, marking it as the northernmost cross-country Interstate.^[102] This designation built on earlier state highway alignments, such as U.S. Route 10, but prioritized new construction for higher design standards, including divided lanes, full control of access, and grade-separated interchanges. Early construction of I-90 emphasized non-toll rural segments in the western states, where vast open terrain allowed for rapid progress under federal guidelines. In Wisconsin, the first Interstate segment in the state—part of what would become the I-90/I-94 corridor—began construction in 1956 near Milwaukee and opened to traffic in 1958 as a 7.5-mile stretch of I-94 in Waukesha County, representing an early win for the system's rollout.^[103] Further west, Montana initiated I-90 builds in the early 1960s, including a key rural section through the Bitterroot Valley near Missoula, completed around 1960 to connect agricultural heartlands and bypass winding two-lane roads.^[104] In Washington, the Vantage segment across the Columbia River plateau opened in 1958, facilitating freight movement through arid plains with minimal urban disruption.^[105] Wyoming's plains construction followed suit in the early 1960s, with a 50-mile stretch between Buffalo and Gillette opening in 1962 to serve ranching and energy transport routes.^[106] One notable early challenge arose in Idaho's Silver Valley, where I-90 planning in the 1960s required a reroute around the historic mining town of Wallace to avoid demolishing its core; local opposition, led by residents protecting the community's mining heritage, delayed the elevated viaduct bypass for over two decades, with the final 4,400-foot section opening on September 12, 1991, and symbolically removing the last traffic signal on any Interstate. Funding for these initial builds came primarily from the Highway Trust Fund, established by the 1956 Act, which covered 90 percent of costs through federal fuel taxes, leaving states responsible for the remaining 10 percent.^[102] Original projections estimated the full Interstate System at $25 billion over 13 years, but early western rural segments alone highlighted escalating expenses due to terrain and material demands, ultimately pushing total costs to over $114 billion by the system's substantial completion in the 1990s.

Integration of toll roads

The integration of existing and newly constructed toll roads into Interstate 90 (I-90) was a key aspect of the highway's development in the 1950s and early 1960s, facilitated by the Federal-Aid Highway Act of 1956, which permitted the inclusion of qualifying toll facilities to enhance system connectivity without federal funding for their construction. On August 21, 1957, the Bureau of Public Roads (BPR) announced the addition of approximately 2,100 miles of toll roads across 15 states to the Interstate System, including significant portions that formed the backbone of I-90 in the eastern United States. These integrations required toll authorities to meet Interstate design standards, such as full control of access and minimum lane widths, while allowing states to retain toll revenues for maintenance and operations.^[107] In Ohio, the 241-mile Ohio Turnpike, completed in 1955 at a cost of $236 million, was fully integrated into the Interstate System in 1957, with its northeastern segment designated as I-90 from the Pennsylvania state line to near Cleveland. This incorporation spanned 173 miles, connecting directly to the Pennsylvania Turnpike and enabling seamless transcontinental travel without parallel free routes. Similarly, in Indiana, the 156-mile Indiana Toll Road, opened on October 31, 1956, after 20 months of construction costing $300 million, was aligned entirely with I-90 from the Illinois state line to the Ohio border, covering 151 miles and serving as a critical link in the Midwest corridor. The New York State Thruway, constructed in phases during the early 1950s, became the core of I-90 in New York, with the portion from the Pennsylvania state line near Ripley to Albany, designated as I-90 in 1957, spanning 385.48 miles and handling over 100,000 vehicles daily by the late 1950s. In Massachusetts, the Massachusetts Turnpike (Mass Pike), initially opened in segments starting in 1957, extended westward to the New York state line near West Stockbridge by May 1957, covering 123 miles from near Boston to the New York state line near West Stockbridge and integrating as I-90 to complete the northeastern alignment.^[107][97] Urban upgrades further incorporated toll elements into I-90. The Chicago Skyway, a 7.8-mile elevated toll bridge built by the City of Chicago and opened on October 24, 1958, at a cost of $31.5 million, connected the Indiana Toll Road to downtown Chicago and was designated as part of I-90 in the mid-1960s following route number swaps in the area. In Pennsylvania, a brief non-toll link was constructed in the late 1950s to bridge the Ohio and New York toll facilities, with the 66-mile I-90 segment from the Ohio border to the New York line built as a free highway under state funding to avoid duplicating the proposed Northwestern Extension of the Pennsylvania Turnpike. These integrations addressed urban bottlenecks while maintaining toll-free access in Pennsylvania.^[52][72] Challenges in these integrations stemmed from negotiations between federal authorities, state governments, and toll commissions to ensure compliance with Interstate standards without federal reimbursement for existing facilities. States like Ohio and Indiana entered agreements allowing BPR oversight of design modifications, such as adding interchanges, in exchange for designating the roads as Interstates, which boosted prestige and traffic volumes. Toll revenues, projected to cover maintenance indefinitely—such as the Ohio Turnpike's $10 million annual collections by 1957—provided financial independence but required ongoing investments to meet evolving safety and capacity requirements. These agreements resolved earlier debates over tolling's compatibility with the free-road vision of the Interstate System, ultimately incorporating over 1,000 miles of I-90's eastern route as toll facilities.^[102][97]

Completion and post-1990s projects

The final segments of Interstate 90 were completed in the early 1990s and early 2000s, marking the full realization of the route across the United States. In Washington, the last 7-mile section near Seattle opened to traffic on September 12, 1993, with the rebuilt Lacey V. Murrow Memorial Bridge over Lake Washington, which had been replaced after the original structure sank during seismic retrofitting in 1990; this segment cost $1.56 billion, reflecting extensive engineering for the floating bridge design.^[108] In Massachusetts, the eastern extension of I-90 into downtown Boston via the Ted Williams Tunnel was finished in 2003 as part of the Central Artery/Tunnel Project (Big Dig), connecting the Massachusetts Turnpike directly to Logan International Airport and alleviating surface congestion.^[89] These completions established I-90's total length at 3,021 miles across 13 states, from Seattle, Washington, to Boston, Massachusetts.^[109] Post-1990s projects have focused on rehabilitation, safety enhancements, and capacity improvements to address aging infrastructure and growing traffic demands. In Ohio, the Cleveland Inner Belt modernization, spanning the 2010s, rebuilt key sections of I-90 through downtown Cleveland, including the replacement of the structurally deficient Innerbelt Bridge over the Cuyahoga River; the new eastbound George V. Voinovich Bridge opened in September 2016, with overall construction from 2011 to 2015 improving seismic resilience and reducing congestion.^[69] In Idaho, rehabilitation efforts in the Kellogg area during the 2000s addressed environmental impacts from historical mining, including treatment of acid mine drainage from the Kellogg Tunnel that affects nearby waterways along I-90, as part of broader Superfund remediation to restore water quality in the Coeur d'Alene River basin.^[110] More recent initiatives from 2020 to 2025 have emphasized bridge reconstructions and interchange upgrades. In Illinois, the $169 million Kennedy Expressway Bridge Rehabilitation Project rehabilitated 36 structures along I-90/94 from the Edens Expressway junction to Irving Park Road, addressing 50-year-old deterioration; the work, which included deck replacements and seismic upgrades, was completed in October 2025, one month ahead of schedule.^[50] In Ohio, the I-90 Major Reconstruction from State Route 2 to SR 611 added a third lane in each direction, replaced pavement, and upgraded bridges to enhance safety and reduce maintenance; this $173 million effort began in August 2025 and is scheduled for completion in October 2028.^[67] In Pennsylvania, a $37.6 million reconstruction of I-90 in Erie County from 2019 to 2021 replaced the Huntley Road overpass with a higher-clearance structure and resurfaced 6.85 miles of roadway to improve ride quality and emergency vehicle access near the Ohio border.^[72] Ongoing safety and connectivity projects continue to modernize the corridor. In Washington, the I-90 Guardrail Basic Safety Rehabilitation replaced and upgraded guardrails along 80 miles from milepost 192 in Adams County to milepost 272.60 in Spokane County, enhancing crash protection; work was substantially completed in 2024.^[111] In Idaho, the I-90/SH-41 interchange in Post Falls was redesigned as a single-point urban interchange to reduce weaving and improve traffic flow, with partial openings in September 2025 and full completion expected in 2026.^[112] In South Dakota, bridge work at the I-90/US 52 area near the Minnesota border included reconstructing overpasses and ramps as part of the I-90/Hwy 52 interchange project, with major beam-setting and paving phases in 2025 to accommodate higher vertical clearances. As of November 14, 2025, the new eastbound I-90 bridge and Hwy 52 flyover bridge were completed and opened to traffic, advancing the project toward full completion in 2026.^[113][114]

Designations and names

Official designations

Interstate 90 is a key component of the National Highway System (NHS), a network of approximately 160,000 miles of roads designated by Congress in 1995 as critical to the nation's economy, defense, and mobility, with the entire Interstate System, including I-90, integrated into this framework. It also forms part of the National Network (NN), established under the Surface Transportation Assistance Act of 1982, which permits commercial trucks up to federal size and weight limits—such as 80,000 pounds gross vehicle weight—without further state-imposed restrictions beyond standard regulations.^[115] The route measures 3,020.54 miles (4,861.57 km) in total length, extending from its western terminus at State Route 519 in Seattle, Washington, to its eastern end near Logan International Airport in Boston, Massachusetts, making it the longest Interstate Highway in the United States.^[1] Approximately 25% of I-90 consists of tolled segments, primarily comprising the portion of the Ohio Turnpike cosigned with I-90 (about 143 miles), the Indiana Toll Road (157 miles), the New York State Thruway (296 miles along I-90), and the Massachusetts Turnpike (138 miles), while the remaining portions are toll-free.^[116] Electronic toll collection via E-ZPass has been interoperable across these facilities since the mid-1990s, following the formation of the E-ZPass Interagency Group in 1990 and initial implementations on the New York State Thruway in 1993, enabling seamless transponder use for drivers traveling multiple states.^[117] Traffic volumes on I-90 vary significantly, with the highest average annual daily traffic (AADT) recorded in the Chicago metropolitan area during the 2010s, exceeding 300,000 vehicles per day on segments through the city, underscoring its role as a major freight and commuter corridor.^[118] Maintenance responsibilities for I-90 lie with individual state departments of transportation (DOTs), which handle day-to-day operations, resurfacing, and rehabilitation, supported by federal funding from the Federal Highway Administration's Interstate Maintenance (IM) program at a 90-10 federal-state matching ratio to ensure long-term preservation.^[119] Although certain segments, such as the Mountains to Sound Greenway in Washington, hold National Scenic Byway status, I-90 as a whole lacks an overarching federal scenic byway designation.^[120]

Memorial and honorary names

Several segments of Interstate 90 have been designated with memorial or honorary names to honor military veterans, particularly those who have served in combat or sustained injuries. One prominent example is the Purple Heart Trail, which recognizes recipients of the Purple Heart medal awarded to U.S. service members wounded or killed in action. This designation applies to the entirety of I-90 in Idaho, Montana, South Dakota, and Wyoming, forming a continuous honorary route across these states as part of the national network established by the Military Order of the Purple Heart.^[121][122] In Idaho, the full length of I-90 was officially named the Purple Heart Trail through state legislation, with the Idaho Transportation Department authorized to erect appropriate signage.^[121] Montana similarly designates its I-90 corridor as the Purple Heart Trail under Montana Code Annotated § 60-1-210, emphasizing tribute to wounded veterans traveling the route. South Dakota's portion of I-90, spanning from the Wyoming border to the Minnesota border, received this designation to commemorate the Purple Heart's legacy, with a formal dedication ceremony held in 2012 to highlight its significance for veterans.^[123] In Wyoming, I-90 is included in the Purple Heart Trail network, with markers such as the one in Laramie serving as visual tributes to combat veterans along the highway.^[124] These designations collectively underscore I-90's role in honoring Purple Heart recipients since the trail's national inception in 1992.^[125] The western segments of I-90 in Washington and Minnesota are named the American Veterans Memorial Highway, paying homage to American veterans from World War II onward. In Washington, State Route 90—concurrent with I-90—is explicitly designated as the American Veterans Memorial Highway under Revised Code of Washington § 47.17.140, recognizing the sacrifices of veterans across conflicts.^[126] Minnesota's legislature similarly named its I-90 trunk highway the American Veterans Memorial Highway via Minnesota Statutes § 161.14, with signage to commemorate veterans' service.^[127] This honorary name highlights the route's importance as a corridor for reflection on military contributions. Further east, I-90 receives the AMVETS Memorial Highway designation in Ohio, Pennsylvania, and New York, honoring members of the American Veterans organization (AMVETS), which supports post-World War II veterans and their families. In Ohio, the non-tolled section of I-90 from the Pennsylvania border in Ashtabula County to its junction with the Ohio Turnpike in Lorain County is known as the AMVETS Highway per Ohio Revised Code § 5533.35.^[128] Pennsylvania designates its entire I-90 route as the AMVETS Memorial Highway through Act 110 of 1990, with signs at state lines to mark the tribute.^[129] In New York, the designation extends along I-90, including the tolled New York State Thruway, as a memorial to AMVETS and broader veteran service.^[72] These names reflect coordinated efforts across states to memorialize veterans' enduring legacy along I-90.

Connections and routes

Major junctions and interchanges

Interstate 90, the longest Interstate Highway in the United States at 3,020 miles, intersects numerous other major Interstate and U.S. highways, facilitating transcontinental travel and freight movement. In its western segment, I-90 connects with I-5 at its terminus in Seattle, Washington, providing access to the Pacific Northwest's urban corridor, and with I-405 near Bellevue, Washington, serving the Seattle metropolitan area.^[130] Further east, central portions feature critical links such as I-94 in Montana, South Dakota, and Minnesota for regional connectivity; I-25 in Wyoming near Buffalo for access to the Rockies; I-29 in South Dakota at Sioux Falls for ties to the Midwest; and overlaps with I-80 and I-94 in Illinois and Indiana, integrating it into the Chicago hub. It intersects I-35 in Minnesota near Albert Lea. In the eastern half, I-90 joins I-71 in Ohio near Cleveland, enhancing Great Lakes commerce, and connects to I-86 in Pennsylvania and New York for efficient routing through the Appalachians without overlap. Additional key connections include I-87 near Albany, New York, linking to the Northeast, and I-95 in Massachusetts near Boston, completing the coast-to-coast chain. These junctions underscore I-90's role as a backbone for national logistics, with many designed as high-capacity systems interchanges to handle heavy traffic volumes.^[130] Notable complex interchanges highlight engineering feats along the route. The Jane Byrne Interchange (formerly Circle Interchange) in Chicago, Illinois, at the convergence of I-90, I-94, and I-290, manages over 400,000 vehicles daily through a multi-level design reconstructed in 2013 for improved flow, with further phases ongoing as of 2025. In Boston, Massachusetts, the Prudential Center interchange connects I-90 to local arterials and the Tip O'Neill Tunnel, integrating with the city's dense urban grid near Logan International Airport. The following table summarizes over 20 significant junctions, focusing on system interchanges with other Interstates and major U.S. highways, listed by approximate milepost from the western terminus (sources include state DOT interchange guides and FHWA corridor studies for verification). Mileposts corrected to cumulative based on official lengths.

Auxiliary and business routes

Interstate 90 has several auxiliary routes that branch off the mainline to provide urban relief, airport access, and connections to key destinations, primarily concentrated in New York and Illinois, totaling approximately 200 miles in length. These routes follow the numbering convention for auxiliary interstates, incorporating "90" as the parent route identifier to indicate their relationship. Business routes, designated as I-90 Business, exist in several smaller towns across South Dakota and Montana to serve central business districts while the mainline bypasses them. In New York, where the majority of auxiliary mileage is located, I-190 serves as a 28.34-mile spur from I-90 near Buffalo northward to the Lewiston–Queenston Bridge at the Canadian border, providing essential access to Buffalo Niagara International Airport and Niagara Falls. I-290, a 17.03-mile route in the Buffalo area, functions as a northern beltway connecting I-90 to I-190 and local highways, alleviating congestion in the urban core. Further east, I-390 in Rochester spans 41.72 miles as a southern connector from I-90 to I-86, supporting regional travel to the Finger Lakes and beyond. I-490 in Syracuse covers 27.80 miles as an inner loop around the city, linking I-90 with I-81 and I-690 for downtown access. I-690, a 14.49-mile auxiliary in Syracuse, branches from I-90 to connect with I-81, serving as a key urban distributor. Shorter routes include I-790 (0.75 miles in Utica, connecting I-90 to downtown), I-890 (9.14 miles near Schenectady as a Thruway bypass), and I-990 (6.29 miles in Amherst near Buffalo, linking I-90 to I-290).^[134] In Illinois, I-290 extends 29.84 miles from I-90 near Chicago to O'Hare International Airport and points west, acting as a vital urban relief route integrated into the Eisenhower Expressway system. A separate I-290 in New York is noted above. Business routes of I-90 are shorter loops designed for local traffic in rural and small urban areas. Examples include the 7.5-mile I-90 Business in Billings, Montana, which connects the mainline to downtown via US 87, and the 8.2-mile loop in Rapid City, South Dakota, providing access to business districts off the main bypass. Similar business alignments exist in towns like Spearfish, South Dakota (3.4 miles), and several Montana communities such as Livingston and Bozeman, totaling under 50 miles combined and emphasizing economic connectivity without the full freeway standards of auxiliaries. These routes ensure continued access to historic commercial areas as I-90's construction rerouted through-traffic.

Significance and impacts

Economic importance

Interstate 90 serves as a critical artery for freight transportation across its 3,021-mile span, facilitating the movement of goods essential to regional economies. In New York State alone, I-90 supports through-truck flows valued at $311.3 billion annually as of 2021, representing a substantial portion of the state's $981.8 billion total truck freight value and underscoring its role in connecting the Northeast to broader markets.^[135] This corridor is particularly vital for Midwest manufacturing, enabling the transport of steel products from facilities in the Chicago metropolitan area and automotive components from Ohio's industrial hubs, while also supporting energy shipments, including coal from Wyoming's Powder River Basin via parallel trucking routes.^[64] In the Minnesota-Wisconsin segment, I-90 qualifies as a Tier 2 nationally significant freight corridor, handling high volumes of agricultural and manufactured goods that bolster the region's economic output.^[64] The highway also connects major corporate centers, enhancing business accessibility and growth. Near Chicago, I-90's Jane Addams Memorial Tollway provides direct access to 15 Fortune 500 headquarters in the metropolitan area as of 2025, including giants like McDonald's and United Airlines, which rely on the route for logistics and employee commuting.^[136] At its eastern terminus in Boston, I-90 links to financial and tech firms such as State Street Corporation, a Fortune 500 entity, facilitating efficient distribution and regional operations. In upstate New York, the corridor supports small business expansion through the 2024 NY SMART I-Corridor Tech Hub designation, which spans Buffalo to Syracuse and has secured $40 million in federal funding to foster semiconductor and microelectronics industries, addressing gaps in lending and entrepreneurial support for local firms.^[137][138] Tourism along I-90 generates significant economic activity by providing access to iconic natural sites, particularly in the western states. The route's passage through South Dakota offers gateways to Badlands National Park, contributing to the state's national park sites' $524 million in visitor spending and over 5,200 jobs in 2024.^[139] Similarly, I-90's proximity to Yellowstone National Park in Montana and Wyoming drives $828 million in local economic benefits from 4.5 million visitors in 2023, supporting sectors like lodging and recreation while aiding recovery in rural communities.^[140] In the I-90 corridor of upstate New York, these tourism inflows complement efforts to revive areas hit by de-industrialization, where manufacturing employment declined sharply over decades, by promoting service-based growth and value-added facilities like distribution centers.^[141][138] Overall, I-90 contributes to the broader interstate system's multiplier effect, generating over $283 billion in additional U.S. economic output through enhanced connectivity and efficiency since its inception.^[142] By linking manufacturing hubs, corporate centers, and tourist destinations, the highway sustains jobs and GDP growth across diverse regions, from industrial Midwest transport to tech-driven revitalization in the Northeast. As of 2025, ongoing Bipartisan Infrastructure Law-funded projects continue to enhance freight efficiency along I-90.

Environmental and safety considerations

Interstate 90 traverses diverse ecosystems, contributing to habitat fragmentation and wildlife-vehicle collisions, particularly in western states. In Montana, where the highway cuts through bison migration routes and forested areas, the installation of wildlife crossings, including overpasses and underpasses, has significantly reduced roadkill. For instance, bison overpasses along I-90 segments near Bozeman have decreased wildlife collisions by up to 90%, allowing safer passage for large mammals and minimizing ecological disruptions. In Washington, environmental impact statements (EIS) for I-90 expansion projects, such as the Snoqualmie Pass corridor, highlight substantial carbon emissions from heavy traffic volumes and ongoing habitat fragmentation affecting local forests and wetlands. These assessments note contributions to regional air quality issues from vehicle emissions. Climate change poses increasing vulnerabilities to I-90 infrastructure, with rising incidences of extreme weather events. In New York, intensified flooding in the Hudson Valley has repeatedly closed sections of I-90, as seen in 2023 storms that caused washouts and required multimillion-dollar repairs due to heavier precipitation patterns. Similarly, the Massachusetts Turnpike portion of I-90 experiences frequent flooding from nor'easters and meltwater, leading to structural erosion along culverts and bridges. In the northern Rockies, harsher winters in Montana and Wyoming have escalated maintenance costs for I-90, with wetter snowfalls increasing avalanche risks and de-icing chemical use. Federal Highway Administration reports indicate expected increases in extreme weather disruptions on major interstates like I-90 in coming decades, potentially adding billions in nationwide repair expenses. Safety concerns along I-90 are pronounced due to high traffic densities and environmental hazards. In the Chicago metropolitan area, where average annual daily traffic (AADT) exceeds 300,000 vehicles on segments like the Dan Ryan Expressway, accident rates are among the highest nationally, with over 15,000 crashes reported annually, often involving multi-vehicle pileups. In Montana, truck-related incidents on I-90 raise ongoing safety concerns, as steep grades and high winds contribute to rollover risks for commercial carriers hauling freight across the state. Winter conditions amplify dangers, with black ice on mountain passes like Snoqualmie in Washington and Lookout in Wyoming causing numerous skids and fatalities each season. The overall U.S. motor vehicle fatality rate was 1.26 deaths per 100 million vehicle miles traveled (VMT) in 2023, with rates on rural interstate stretches often higher due to lower visibility, wildlife intrusions, and delayed emergency response.^[143] Efforts to mitigate these environmental and safety issues include targeted federal and state initiatives. The 2022 Bipartisan Infrastructure Law allocated $350 million for wildlife crossing projects nationwide, funding enhancements along I-90 in Montana to further integrate eco-passages and fencing. In Washington, the planned 2026 expansion of light rail across I-90 via the East Link extension is projected to reduce emissions by shifting commuters from vehicles, while also easing traffic congestion and collision risks.