Editing Interstate 90 (section)

===Montana===
{{Main|Interstate 90 in Montana}}
[[File:I-90 eastbound at Lookout Pass on the Idaho-Montana border.jpg|thumb|right|I-90 at [[Lookout Pass]] on the Idaho–Montana border|alt=A simple overpass over a divided highway seen from a grassy area on the side of the road]]

Montana has the longest section of I-90, at almost {{convert|552|mi|km}}, despite the highway only serving a portion of the state's east–west width.<ref name="FHWA-Routes"/><ref name="MT-Map">{{cite map |year=2021 |title=Montana Official Highway Map |url=https://mdt.mt.gov/travinfo/docs/2021-mt-highway-map.pdf |location=Helena |publisher=[[Montana Department of Transportation]] |scale=Scale not given |accessdate=November 29, 2021 |archive-date=December 1, 2021 |archive-url=https://web.archive.org/web/20211201004352/https://mdt.mt.gov/travinfo/docs/2021-mt-highway-map.pdf |url-status=live }}</ref> It descends from Lookout Pass along the [[St. Regis River (Montana)|St. Regis]] and [[Clark Fork River|Clark Fork]] rivers between the foothills of the Bitteroot Range and [[Coeur d'Alene Mountains]]. The freeway travels east through the [[Alberton, Montana|Alberton Gorge]] and crosses the Clark Fork River several times before it reaches the head of the [[Missoula Valley]].<ref>{{cite news |last=Gadbow |first=Daryl |date=July 22, 2004 |title=Gorgeous Gorge |page=C1 |work=[[The Missoulian]] |url=https://www.newspapers.com/clip/89736594/gorgeous-gorge/ |via=Newspapers.com |accessdate=November 29, 2021 |archive-date=November 29, 2021 |archive-url=https://web.archive.org/web/20211129085211/https://www.newspapers.com/clip/89736594/gorgeous-gorge/ |url-status=live }}</ref> After a short concurrency with [[U.S. Route 93|US&nbsp;93]], I-90 runs along the north side of [[Missoula, Montana|Missoula]] and joins [[U.S. Route 12|US&nbsp;12]] to continue southeast along the foothills of the [[Garnet Range]] and [[Sapphire Mountains]].<ref name="MT-Map"/>

After it splits from US&nbsp;12 in [[Garrison, Montana|Garrison]], the freeway turns south to traverse the [[Deer Lodge Valley]]. It then turns east to serve [[Butte, Montana|Butte]], where it overlaps with [[Interstate 15|I-15]] for {{convert|8|mi|km|spell=in}} and intersects [[Interstate 115|I-115]]. I-90 then continues southeast and crosses the [[Rocky Mountains]] and [[Continental Divide of the Americas|Continental Divide]] at [[Homestake Pass]], which is the highest point on the entire Interstate at {{convert|6329|ft|m}}.<ref>{{cite news |last=Smith |first=Mike |date=September 22, 2016 |title=Slower speed limit in works for most of Homestake Pass |page=A1 |work=[[The Montana Standard]] |url=https://www.newspapers.com/clip/89736816/slower-speed-limit-in-works-for-most-of/ |via=Newspapers.com |accessdate=November 29, 2021 |archive-date=November 29, 2021 |archive-url=https://web.archive.org/web/20211129085211/https://www.newspapers.com/clip/89736816/slower-speed-limit-in-works-for-most-of/ |url-status=live }}</ref> The freeway travels east across the [[Jefferson River|Jefferson Valley]] and passes the headwaters of the [[Missouri River]] near [[Three Forks, Montana|Three Forks]]. It then enters the [[Gallatin Valley]].<ref name="MT-Map"/><ref>{{cite news |last=Jokerst |first=Gail |date=June 10, 2001 |title=Headwaters haven: Three Forks a quaint slice of Montana's history |page=H4 |work=The Spokesman-Review |url=https://www.newspapers.com/clip/89737271/headwaters-haven-three-forks-a-quaint/ |via=Newspapers.com |accessdate=November 29, 2021 |archive-date=November 29, 2021 |archive-url=https://web.archive.org/web/20211129091500/https://www.newspapers.com/clip/89737271/headwaters-haven-three-forks-a-quaint/ |url-status=live }}</ref>

I-90 travels around [[Bozeman, Montana|Bozeman]], where it is joined by [[U.S. Route 191|US&nbsp;191]], and crosses [[Bozeman Pass]] between the [[Bridger Mountains (Montana)|Bridger]] and [[Gallatin Range|Gallatin]] mountains. At the east end of the mountains, the freeway begins to follow the [[Yellowstone River]] and is briefly concurrent with [[U.S. Route 89|US&nbsp;89]], which serves [[Yellowstone National Park]], and splits from US&nbsp;191 at [[Big Timber, Montana|Big Timber]]. I-90 continues along the Yellowstone River through [[Billings, Montana|Billings]], overlapping with [[U.S. Route 87|US&nbsp;87]] and [[U.S. Route 212|US&nbsp;212]], until it reaches [[Lockwood, Montana|Lockwood]], the western terminus of [[Interstate 94|I-94]]. The freeways split and I-90 continues east across the [[Bighorn Basin]] before it turns south near [[Hardin, Montana|Hardin]] to follow the [[Little Bighorn River]] into the [[Crow Indian Reservation]]. The highway passes [[Little Bighorn Battlefield National Monument|the site]] of the [[Battle of the Little Bighorn]] near [[Crow Agency, Montana|Crow Agency]] and continues south along the river and the [[Wolf Mountains]] into Wyoming.<ref name="MT-Map"/><ref>{{cite news |last=Pyle |first=Richard |date=August 17, 2003 |title=The victors at Little Bighorn |page=N5 |work=[[The Philadelphia Inquirer]] |url=https://www.newspapers.com/clip/89737083/the-victors-at-little-bighorn/ |via=Newspapers.com |accessdate=November 29, 2021 |archive-date=November 29, 2021 |archive-url=https://web.archive.org/web/20211129085212/https://www.newspapers.com/clip/89737083/the-victors-at-little-bighorn/ |url-status=live }}</ref>

From 1995 to 1999, there was no numbered daytime [[Speed limits in the United States|speed limit]] on rural highways in Montana, including I-90.<ref>{{cite news |last=Whitely |first=Peyton |date=December 10, 1995 |title=With a roar, Montana drops day speed limit |page=A1 |url=https://archive.seattletimes.com/archive/?date=19951210&slug=2157057 |work=The Seattle Times |accessdate=November 29, 2021 |archive-date=November 29, 2021 |archive-url=https://web.archive.org/web/20211129090327/https://archive.seattletimes.com/archive/?date=19951210&slug=2157057 |url-status=live }}</ref> The speed limit was simply defined as "reasonable and proper" as determined on a case-by-case basis by the [[Montana Highway Patrol]] until the [[Montana Supreme Court]] ruled it was unconstitutional.<ref>{{cite news |last=Robbins |first=Jim |date=December 25, 1998 |title=Montana's Speed Limit of ?? M.P.H. Is Overturned as Too Vague |page=A20 |url=https://www.nytimes.com/1998/12/25/us/montana-s-speed-limit-of-mph-is-overturned-as-too-vague.html |work=[[The New York Times]] |accessdate=November 29, 2021 |archive-date=November 29, 2021 |archive-url=https://web.archive.org/web/20211129090327/https://www.nytimes.com/1998/12/25/us/montana-s-speed-limit-of-mph-is-overturned-as-too-vague.html |url-status=live }}</ref> The maximum daytime speed limit in Montana was initially set at {{convert|75|mph|km/h|abbr=on|round=5}} in 1999 and was later raised to {{convert|80|mph|km/h|abbr=on|round=5}} in 2015.<ref>{{cite news |last=Carter |first=Troy |date=October 1, 1995 |title=Montana interstate speed limit raised to 80 mph—mostly |url=https://www.bozemandailychronicle.com/news/montana-interstate-speed-limit-raised-to-80-mph-mostly/article_7dee866c-c7ca-5002-aee3-72c6335fd1be.html |work=[[Bozeman Daily Chronicle]] |url-status=dead |archive-url=https://web.archive.org/web/20211129090331/https://www.bozemandailychronicle.com/news/montana-interstate-speed-limit-raised-to-80-mph-mostly/article_7dee866c-c7ca-5002-aee3-72c6335fd1be.html |archive-date=November 29, 2021 |accessdate=November 29, 2021}}</ref>