Interstate 90 (I-90) is an east–west transcontinental

Interstate Highway The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, or the Eisenhower Interstate System, is a network of controlled-access highways that forms part of the National Hi ...

across the northern

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

, linking

Seattle Seattle ( ) is the most populous city in the U.S. state of Washington and in the Pacific Northwest region of North America. With a population of 780,995 in 2024, it is the 18th-most populous city in the United States. The city is the cou ...

Boston Boston is the capital and most populous city in the Commonwealth (U.S. state), Commonwealth of Massachusetts in the United States. The city serves as the cultural and Financial centre, financial center of New England, a region of the Northeas ...

. The portion in the state of

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

is in length, passing through 14 counties in central and southern Montana. It is the longest segment of I-90 within a single state.

Route description

Mineral County

I-90 enters Montana and Mineral County from Shoshone County, Idaho over the high Lookout Pass, which traverses the

Coeur d'Alene Mountains The Coeur d'Alene Mountains are the northwesternmost portion of the Bitterroot Range, part of the Rocky Mountains, located in northern Idaho Idaho ( ) is a landlocked U.S. state, state in the Pacific Northwest and Mountain states, Mount ...

of the

Bitterroot Range The Bitterroot Range is a mountain range and a subrange of the Rocky Mountains that runs along the border of Montana and Idaho in the northwestern United States. The range spans an area of and is named after the bitterroot (''Lewisia rediviva ...

, and immediately has its first

interchange Interchange may refer to: Transport * Interchange (road), a collection of ramps, exits, and entrances between two or more highways * Interchange (freight rail), the transfer of freight cars between railroad companies * Interchange station, a rai ...

, a

partial cloverleaf interchange A partial cloverleaf interchange or parclo is a modification of a cloverleaf interchange. The design has been well received, and has since become one of the most popular freeway-to-arterial interchange designs in North America. It has also bee ...

serving extreme northwest Mineral County and access to

Lookout Pass Ski and Recreation Area Lookout Pass Ski and Recreation Area is a ski area in the western United States. It is at Lookout Pass on Interstate 90, on the border of Idaho and Montana, east of Mullan, Idaho. It has a summit elevation of on Eagle Peak and on Runt Mount ...

. The highway continues southeasterly through woodlands, paralleling the

St. Regis River The St. Regis River (or rivière Saint-Régis in Quebec) is an river in northern New York (state), New York in the United States. It flows into the Saint Lawrence River at the hamlet of Saint Regis, New York, Saint Regis in the St. Regis Moha ...

, before meeting the Dena Mora (Lookout Pass)

rest area A rest area is a public facility located next to a large thoroughfare such as a motorway, Limited-access road, expressway, or highway, at which drivers and passengers can rest, eat, or refuel without exiting onto secondary roads. Other names ...

east of the Idaho–Montana border. About from the rest stop is a

diamond interchange A diamond interchange is a common type of road junction, used where a controlled-access highway crosses a minor road. Design The freeway itself is grade separation, grade-separated from the minor road, one crossing the other over a bridge. ...

, serving a small minor road into the St. Joe National Forest in Idaho. The highway continues, winding through the woodlands until another diamond interchange, serving the small

unincorporated community An unincorporated area is a parcel of land that is not governed by a local general-purpose municipal corporation. (At p. 178.) They may be governed or serviced by an encompassing unit (such as a county) or another branch of the state (such as th ...

of Saltese. Continuing east for about , each direction diverges for a small distance before returning side to side for a diamond interchange serving the unincorporated community of Haugan. after Haugan, I-90 intersects the

census-designated place A census-designated place (CDP) is a Place (United States Census Bureau), concentration of population defined by the United States Census Bureau for statistical purposes only. CDPs have been used in each decennial census since 1980 as the counte ...

(CDP) of De Borgia, continuing southeasterly, intersecting several minor roads, before reaching the CDP of St. Regis and Montana Highway 135 (MT 135). The highway stops paralleling the St. Regis River, and begins to parallel, and cross over several times, the

Clark Fork River The Clark Fork, or the Clark Fork of the Columbia River, is a river in the U.S. states of Montana and Idaho, approximately long. It is named after William Clark of the 1806 Lewis and Clark Expedition. The largest river by volume in Montana, it ...

Superior Superior may refer to: *Superior (hierarchy), something which is higher in a hierarchical structure of any kind Places * Superior (proposed U.S. state), an unsuccessful proposal for the Upper Peninsula of Michigan to form a separate state *Lak ...

, the

county seat A county seat is an administrative center, seat of government, or capital city of a county or parish (administrative division), civil parish. The term is in use in five countries: Canada, China, Hungary, Romania, and the United States. An equiva ...

, is intersected before the highway turns south through the Quartz Flats rest area, located from the Idaho border. After leaving the rest area, the highway straightens out, heading easterly. The highway continues east before exiting the county, just south of Alberton.

Missoula, Granite, and Powell counties

Entering Missoula County, the highway intersects Alberton, before continuing easterly through Huson and Secondary Highway 263 (S-263). The highway continues southeast before intersecting the concurrent highways US Highway 93 (US 93) and MT 200, which join I-90 from the west. The three highways continue into the county seat of

Missoula Missoula ( ) is a city in and the county seat of Missoula County, Montana, Missoula County, Montana, United States. It is located along the Clark Fork River near its confluence with the Bitterroot River, Bitterroot and Blackfoot River (Montana), ...

, where, at the first exit, US 93 leaves on the western border of Missoula and travels through Orchard Homes. The next two exits travel into Downtown Missoula, while the last exit serves East Missoula. US 12 joins I-90 and MT 200 exits to the north of the highway outside of Missoula, paralleling the Blackfoot River as I-90 continues east, following and then intersecting S-210 in Clinton. The Bearmouth rest area, from the Idaho border, is intersected before crossing the Missoula–

Granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

county border. After entering Granite County, I-90 has an interchange with an access road to the Garnet Back Country Byway, providing access to the Garnet Range on the west slope of the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in great-circle distance, straight-line distance from the northernmost part of Western Can ...

. The highway passes north of

Lolo National Forest __NOTOC__ Lolo National Forest is a national forest located in western Montana, United States with the western boundary being the state of Idaho. The forest spans 2 million acres (8,000 km2) and includes four wilderness areas; the Scapegoat ...

while headed easterly. The highway continues through northern Granite county, intersecting MT 1 before exiting the county entering Powell County. I-90 intersects S-272 after entering the county, which clips the eastern segment of Lolo National Forest, before the seasonal Gold Creek rest area is intersected.

Garrison A garrison is any body of troops stationed in a particular location, originally to guard it. The term now often applies to certain facilities that constitute a military base or fortified military headquarters. A garrison is usually in a city ...

is northeast of the highway as US 12 ends its concurrency, traveling north from I-90 toward the

state capital Below is an index of pages containing lists of capital city, capital cities. National capitals *List of national capitals *List of national capitals by latitude *List of national capitals by population *List of national capitals by area *List of ...

Helena Helena may refer to: People *Helena (given name), a given name (including a list of people and characters with the name) *Katri Helena (born 1945), Finnish singer * Saint Helena (disambiguation), this includes places Places Greece * Helena ...

. I-90 turns south, paralleling former

Northern Pacific Railway The Northern Pacific Railway was an important American transcontinental railroad that operated across the northern tier of the Western United States, from Minnesota to the Pacific Northwest between 1864 and 1970. It was approved and chartered b ...

trackage, before intersecting S-275 and the county seat, Deer Lodge. Continuing south, I-90 exits Powell County at

Racetrack A race track (racetrack, racing track or racing circuit) is a facility built for racing of vehicles, athletes, or animals (e.g. horse racing or greyhound racing). A race track also may feature grandstands or concourses. Race tracks are also us ...

Deer Lodge, Silver Bow, and Jefferson counties

I-90 bisects the northern tip of Deer Lodge County, in a southwesterly direction.

Galen Aelius Galenus or Claudius Galenus (; September 129 – AD), often Anglicization, anglicized as Galen () or Galen of Pergamon, was a Ancient Rome, Roman and Greeks, Greek physician, surgeon, and Philosophy, philosopher. Considered to be one o ...

and S-273 are intersected, before the highway passes west of the Warm Springs State Wildlife Management Area. After passing the wildlife management area, the highway passes by Warm Springs and MT 48. Just northwest of the Deer Lodge– Silver Bow county border, I-90 intersects MT 1. Fairmont Hot Springs Resort, accessible via S-441, is the first exit in Silver Bow County on I-90, as the highway starts to turn back toward the east.

Ramsay Ramsay may refer to: People * Ramsay (surname), people named Ramsay * Clan Ramsay, a Scottish clan * Ramsay brothers, Indian film makers * Richard Sorge (1895–1944), Soviet spy codenamed "Ramsay" Places Australia * Ramsay, Queensland, a lo ...

is located in the southwest corner of the interchange where

I-15 I15 may refer to: * Interstate 15, a north–south Interstate Highway in the United States of America * Polikarpov I-15, a Soviet fighter aircraft * I15 (band), a band * , of the Imperial Japanese Navy * Älvsborg Regiment The Älvsborg Regiment ...

becomes concurrent with I-90 through

Butte In geomorphology, a butte ( ) is an isolated hill with steep, often vertical sides and a small, relatively flat top; buttes are smaller landforms than mesas, plateaus, and table (landform), tablelands. The word ''butte'' comes from the French l ...

. On the western edge of Butte, I-115 continues east into town, as I-15/I-90 turns southeast, bypassing most of downtown Butte. An interchange with MT 2 serves Bert Mooney Airport before I-15/I-90 split just east of Butte, with I-15 continuing north over the

Continental Divide A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not ...

over the high Elk Park Pass, which straddles the Silver Bow– Jefferson county border. I-90 heads south then east, also entering Jefferson County, passing over the divide at

Homestake Pass Homestake Pass is a mountain pass in the Rocky Mountains of Montana in the United States. It sits on the Continental Divide on the border between Jefferson County and Silver Bow County, six miles south-southeast of Butte in Beaverhead-Deerlod ...

which is high. After traveling the pass, an emergency escape ramp can be found on the highway's eastbound lanes. Jefferson County has interchanges with S-399 east of Pipestone, Montana and S-359 east of Cardwell before meeting the Jefferson– Broadwater county border.

Broadwater, Gallatin, and Park counties

There is only one exit along I-90 in Broadwater County, linking MT 2 in the south and US 287 north of the highway before crossing the Broadwater– Gallatin county border at the

Missouri River The Missouri River is a river in the Central United States, Central and Mountain states, Mountain West regions of the United States. The nation's longest, it rises in the eastern Centennial Mountains of the Bitterroot Range of the Rocky Moun ...

. I-90 parallels S-205, bypassing the towns of

Trident A trident (), () is a three- pronged spear. It is used for spear fishing and historically as a polearm. As compared to an ordinary spear, the three tines increase the chance that a fish will be struck and decrease the chance that a fish will b ...

, Logan,

Manhattan Manhattan ( ) is the most densely populated and geographically smallest of the Boroughs of New York City, five boroughs of New York City. Coextensive with New York County, Manhattan is the County statistics of the United States#Smallest, larg ...

, and

Belgrade Belgrade is the Capital city, capital and List of cities in Serbia, largest city of Serbia. It is located at the confluence of the Sava and Danube rivers and at the crossroads of the Pannonian Basin, Pannonian Plain and the Balkan Peninsula. T ...

on the north of the highway. A new interchange was constructed just east of Belgrade (exit 299) that services Bozeman Yellowstone International Airport to the north and the western area of the city of Bozeman. MT 85 travels south from I-90 in Belgrade, providing access to Bozeman Hot Springs. The highway then enters the city of

Bozeman Bozeman ( ) is a city in and the county seat of Gallatin County, Montana, United States. The 2020 United States census put Bozeman's population at 53,293, making it Montana's fourth-largest city. It is the principal city of the Bozeman, Montan ...

, the county seat, and intersects and becomes concurrent with US 191. I-90 exits the county at the Gallatin–

Park A park is an area of natural, semi-natural or planted space set aside for human enjoyment and recreation or for the protection of wildlife or natural habitats. Urban parks are urban green space, green spaces set aside for recreation inside t ...

county border at high Bozeman Pass. US 89 intersects I-90 in the county seat of Livingston and passes over the

Yellowstone River The Yellowstone River is a tributary of the Missouri River, approximately long, in the Western United States. Considered the principal tributary of the upper Missouri, via its own tributaries it drains an area with headwaters across the mountain ...

. The highway continues northeasterly, paralleling the river, intersecting S-295 before crossing the Park– Sweet Grass county border.

Sweet Grass and Stillwater counties

Still paralleling the Yellowstone River, I-90 travels northwest intersecting S-298 and US 191 in the county seat of Big Timber. The highway turns back southeast, passing south of Greycliff and the Greycliff rest area, located from the Idaho border. The highway passes through the Sweet Grass– Stillwater county border just west of Reed Point. After passing into Stillwater County, I-90 crosses over the river, and enters the county seat of Columbus, intersecting MT 78 south of the highway and S-306 on the north side of the highway. The highway is titled the Robert E. Ewing Jr. Memorial Highway between mileposts 410 and 424. I-90 intersects the Columbus rest area, from the Idaho border, followed by Park City before exiting Stillwater County.

Yellowstone and Big Horn counties

US 212 becomes concurrent with I-90 just east of

Laurel Laurel may refer to: Plants * Lauraceae, the laurel family * Laurel (plant), including a list of trees and plants known as laurel People * Laurel (given name), people with the given name * Laurel (surname), people with the surname * Laurel (mus ...

before entering the county seat of

Billings Billings is the most populous city in the U.S. state of Montana, with a population of 117,116 as of the 2020 census. Located in the south-central portion of the state, it is the seat of Yellowstone County and the principal city of the Billin ...

. I-90 Business (I-90 Bus.) passes into town as the main freeway travels south of Billings and bisects Billings Heights and Lockwood intersecting MT 3 and US 87, which joins the I-90/US 212 concurrency. On the extreme eastern end of Billings, the three highways intersect the western terminus of I-94, which heads northeast toward

North Dakota North Dakota ( ) is a U.S. state in the Upper Midwest, named after the indigenous Dakota people, Dakota and Sioux peoples. It is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minneso ...

, while I-90 turns southeast into Big Horn County. Immediately after entering Big Horn County, the three highways pass the seasonal Hardin rest area. Entering Hardin, the county seat, the three highways intersect S-313 and MT 47. S-313 provides access to Yellowtail Dam, while MT 47 connects back to I-94. After exiting Hardin, I-90 turns south, entering the

Crow Indian Reservation The Crow Indian Reservation is the homeland of the Crow Tribe. Established 1868, the reservation is located in parts of Big Horn, Yellowstone, and Treasure counties in southern Montana in the United States. The Crow Tribe has an enrolled membe ...

and intersects S-384, before reaching

Crow Agency Crow Agency () is a census-designated place (CDP) in Big Horn County, Montana, United States and is near the actual location for the Little Bighorn National Monument and re-enactment produced by the Real Bird family known as Battle of the Lit ...

. Crow Agency is home to

Little Bighorn Battlefield National Monument Little Bighorn Battlefield National Monument preserves the site of the June 25 and 26, 1876, Battle of the Little Bighorn, near Crow Agency, Montana, in the United States. It also serves as a memorial to those who fought in the battle: George A ...

and Reno–Benteen Battlefield Memorial, which are passed after US 212 departs to the east. Continuing south, I-90/US 87 parallels S-451 and the

Little Bighorn River The Little Bighorn River is a tributary of the Bighorn River in the United States in the states of Montana and Wyoming. The Battle of the Little Bighorn, also known as the Battle of the Greasy Grass, was fought on its banks on June 25–26, 187 ...

, passing by Garryowen, Benteen, Lodge Grass, and Wyola before exiting the state of Montana and entering Sheridan County, Wyoming.

History

I-90 replaced US 10 between Livingston and the Idaho border, and, before that, the

Yellowstone Trail The Yellowstone Trail was the first transcontinental automobile highway through the upper tier of states in the United States, established on May 23, 1912. It was an Auto trail, Auto Trail that ran from the Atlantic Ocean in Plymouth, Massachus ...

. Some sections of the highway follow the historic

Mullan Road Mullan Road was the first covered wagon, wagon road to cross the Rocky Mountains to the Inland Empire (Pacific Northwest), Inland of the Pacific Northwest. It was built by United States Army, U.S. Army troops under the command of Lt. John Mullan ( ...

, a military road constructed from 1859 to 1862 between

Fort Walla Walla Fort Walla Walla is a United States Army fort located in Walla Walla, Washington. The first Fort Walla Walla was established July 1856, by Lieutenant Colonel Edward Steptoe, 9th Infantry Regiment. A second Fort Walla Walla was occupied Septe ...

in modern-day Washington and Fort Benton in Montana. The section over

cost $18.5 million (equivalent to $ in ) to construct and was completed on October 30, 1966. The final two-lane section of the highway, near Springdale, was expanded to four lanes in May 1987. Until 1995 in

near the Idaho border, I-90 was not a divided highway for a few stretches, having only a narrow paved

median The median of a set of numbers is the value separating the higher half from the lower half of a Sample (statistics), data sample, a statistical population, population, or a probability distribution. For a data set, it may be thought of as the “ ...

. From 1995 until 1999, the daytime maximum speed limit in Montana was "reasonable and prudent". , the daytime and nighttime speed limits on Interstate Highways are for cars and light trucks and for heavy trucks, except within urban areas, where the maximum speed limit is for all vehicles, day or night. The western have a lower speed limit, as well as the Missoula and Butte urban areas. In 1996, a section of I-90 was closed for 19 days due to a train derailment and

chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

spill near Alberton.

Expansion of the Billings area corridor

The 2012 Billings area I-90 corridor planning study recommends many improvements to the corridor from Laurel through Lockwood, including construction of new east and westbound bridges over the Yellowstone River, with each bridge having three to four traffic lanes. Also recommended are construction of additional eastbound and westbound traffic lanes from Shiloh to Johnson Lane and reconstruction and widening of many of the bridges, interchanges and on/offramps along the corridor at an estimated cost of $114 million.

Exit list

References

External links

{{state detail page browse, type=I, route=90, state=Montana, stateafter=Wyoming, statebefore=Idaho