Interstate construction sequencing in your state

[GaryV]

We lived only 6 blocks from the middle section of I-696, and then later 2 miles north. It sure was nice when it finally got completed. No more having to take 12 Mile Road thru Southfield to get out of town to the west.

[RobbieL2415]

The only addition/clarification in CT:  I-691 was not completed until 1988.  The highway existed from current Exit 5 (former Exit 4) until 1985.  It was extended west to CT 10 (current 7/former 3) that year (BGS's were signed TO 10 SOUTH Cheshire), and then to I-84 in 1988.  At that point, the designation was given, CT 66 was truncated to I-91, and CT 322 was extended to the former endpoint of the freeway.

I also thought that I-291 didn't open until 1994.

[SilverMustang2011]

Anomalies and WTFs: The only one I can think of is the several-year period during which the only connection between Florida's Turnpike I-95 and the rest of I-95 was via about 3/4 mile of FL 70. Of course, no connection was ever provided there-- the gap wasn't closed until the full length of I-95 was completed.

Another Florida Anomaly/WTF: I-75 was originally supposed to end at I-4 in Downtown Tampa with I-4 itself ending in South St Pete and no interstate connection through Southwest Florida was planned. While the decision was reversed by the mid-70s, it really puts into perspective how much that area's population boomed between 1960 and now. Only having the Tamiami Trail as the main route from Tampa to Southeast Florida would be brutal.

[HighwayStar]

I'll have a crack at Montana since I've traveled most of those.


Montana

Construction:

This is mostly based on state highway maps, which have some discrepancies and conflicts.

1957: The portions of I-90 and I-15 west of Butte to Rocker are shown on the map as divided highways. The state legend has no corresponding divided highway however.

1959: Divided highways show on the state map legend for the first time. Interstates are signed on the respective US routes, with additional disclaimers indicating "present interstate routing"

1960:
I-90 east of Drummond to Gold Creek is completed.
I-90 west of Springdale has a short section completed
I-90 west of Garryowen to Crow Agency is completed with a short section beyond Crow Agency as well.
I-15 has a section completed north of Cascade to south of Ulm

1961:
Interstate Highways now have their own map section. Confusingly this includes labels for both 2 and 4 lanes with a minor difference between the 2. Proposed roads are also now shown. Some segments are now shown as "2 lane interstates" but I am excluding these from the completion consideration.
I-15 has a section south of JCT I-90 and north of Buxton completed
I-15 from the north end of Great Falls to Vaugh is completed
I-15 in the vicinity of Shelby is completed
I-90 has a short section near Tarkio completed
I-90 from East Laurel to just West of Billings is Completed

1962:
I-90 From east of Livingston to west of JCT US-89 is completed
I-15 is completed between Helena and Montana City

1963:
Numerous additional sections are shown as interstate but not with multilane construction

1964:
I-90 is completed in the vicinity of Alberton
I-90 is completed from Bear Canyon to Bozeman Pass
I-15 is completed from Helena to Sieben

1965:
I-90 is completed in the vicinity of Huson
I-90 is completed from East Missoula to Turah
I-90 is completed in the vicinity of Opportunity
I-90 is completed from Three Forks to Manhattan, bypassing US-10
I-90 is completed from Laurel to the existing Billings portion
I-94 is completed for a short section east of Bighorn
I-15 at Sweetgrass Port is completed

1966:
I-90 is completed from Superior to Lozeau
I-90 is completed from west of Drummond to the existing Drummond-Gold Creek section
I-90 is completed to west of Butte
I-90 is completed from the existing Manhattan section to Bozeman
I-15 is completed from Wolf Creek south to the existing section at Sieben
In Butte, a 2 lane road from north of the junction with I-90 is shown (this would eventually become I-15)

1967:
This map includes inset maps for major cities which help clarify urban freeway expansion
I-90 is completed from Lozeau to Tarkio
I-90 is completed from west of Frenchtown to East Missoula
I-90 is completed from the Opportunity area to the existing section at JCT I-15
I-90 is completed from west of Butte to east of Whitehall over Homestake Pass, bypassing I-10 over Pipestone Pass
I-90 is completed in the vicinity of Reedpoint
I-90 is completed from Park City to Laurel
I-15 is completed through Great Falls south to the Airport

1968:
I-15 from Wolf Creek to north of Craig is completed

1969:
I-90 is completed to Cardwell
I-94 is completed from Billings to Pompeys Pillar
I-15 is completed from Montana City to Clancy
I-15 has a section south of Cascade completed


1970:
I-90 is completed from west of Bearmouth to the existing Drummond Section
I-94 from east of Terry to West of Fallon is completed
I-94 is completed in the vicinity of Glendive
I-15 is completed south to Ulm from the Great Falls section

1971:
I-90 is completed from west of Barmouth to east of Clinton
I-90 is completed from Cardwell to Three Forks
I-90 is completed from Bozeman to Bear Canyon
I-90 is completed from Park City to east of Columbus
I-90 is completed in the Hardin vicinity
I-94 is completed in the Rosebud vicinity
I-15 is completed from Dell to Red Rock
I-15 is completed from Clancy to Jefferson City
I-15 has a gap between Craig and Cascade filled, completing I-15 from Helena to south of Cascade
I-15 is completed from Oilmont to Sunburst

1972:
Map Unavailable

1973:
I-90 is completed from Lookout pass to Salteese
I-90 is completed from Huson to the Missoula section
I-90 is completed from Clinton to Bearmouth
I-90 is completed from Greycliff to Reed Point
I-90 is completed from Hardin to Billings
I-94 is completed from Hathaway to Horton
I-94 is completed west from the existing Terry-Fallon section to 20 miles west of Terry
I-15 a section from Dell south to north of Lima is completed
I-15 is completed from Vaughn to south of Dutton
I-15 is completed from Conrad to south of Shelby

1974:
I-90 is completed in the vicinity of Deer Lodge
I-90 is completed from Columbus to east of Reed Point
I-94 is completed near Custer
I-94 is completed for another segment between Fallon and Glendive
I-15 is completed from Dillon to Melrose
I-15 is completed from Jefferson City to Bolder
US-91 is resigned to the future I-15 alignment on the Butte inset map

1975:
I-90 is completed further south of Deer Lodge, about 5 miles
I-94 is completed from Horton to the far side of Miles City

1976:
I-90 is completed from Haugan to De Borgia
I-94 is completed from Pompeys Pillar to the existing section west of Custer
I-94 is completed from Wibaux to the North Dakota state line
I-15 is completed from north of Melrose to Buxton over the Continental Divide

1977:
I-90 a gap between Reed Point and Columbus is Closed
I-94 the gap between the Bighorn and west of Forsyth sections is completed
I-94 the gap between the Rosebud and Miles City section near Hathaway is completed
I-94 a gap between Glendive and the section west of Glendive is completed
I-15 the section in Elk Park is completed
I-15 the section between Dutton and Conrad is completed

1978:
I-94 the gap between sections from west of Forsyth to Rosebud is completed
I-94 a gap between the Terry and Glendive sections is completed
I-15 a gap south of Shelby is completed to the Conrad section

1979-1980:
I-90 the gap from Deer Lodge to Opportunity is completed
I-94 a short gap near Custer is completed

1981-1982:
I-90 the section from DeBorgia to West of St. Regis is completed
I-90 the section west of St. Regis is completed
I-90 the section over Bozeman Pass is completed closing the gap between the Boseman and Livingston segments
I-90 the section from Greycliff to De Hart is completed
I-90 the section from Garryowen to Lodge Grass is completed
I-15 the section from Monita to north of Lima is completed
I-15 the section from Clark Canyon to Red Rock is completed
I-15 the section from Shelby to Oilmont is completed
I-15 the section from Sunburst to Sweetgrass is completed
I-94 the section from Glendive to Wixbaux is completed

1983-1984:
I-90 the section between Springdale and De Hart is completed

1985-1986:
I-90 the gap at St. Regis is completed
I-90 the gap between St. Regis and Superior is completed
I-90 the gap between tarkio and Alberton is completed
I-90 the gap between Alberton and Huson is completed
I-94 the gap between miles City and Terry is completed (this completes I-94 in Montana)
I-15 is completed from Dillon south to Barrets
I-15 is completed south of Boulder to exit 160

1987-1988:
I-90 a gap near Springdale is completed (this completes I-90 in Montana)
I-90 is completed from Lodge Grass to the Wyoming State Line
I-15 the gap between Clark Canyon and Baretts is completed
I-15 the gap between North Elk Park and Basin is completed (this completes I-15 in Montana)

Pre-Interstate factors:
None

Sequencing Strategy:
Montana was fairly strategic in the sense that construction mostly focused on the more populated western half of the state with I-90 and I-15 versus the relatively sparsely populated eastern half with I-94. Higher traffic areas generally seem to have interstates built out first. However some segments were not completed until the 80's which would have carried far more traffic than some which were completed a decade earlier. Later construction seemed to favor longer segments being completed at once and building off existing segments.

Urban vs Rural:
In Montana this is a relative distinction, but there does seem to be some priority given to urban areas. Butte, the largest and most important city in the state when the interstate system was created, received some of the first interstate construction on the west side which connected to the Anaconda area 25 miles distant.
By 1965 Butte, Great Falls, Billings, and Missoula all had some interstate connections on at least one side of the city. And by 1967 Butte, Helena, Great Falls, Billings, and Missoula all had their urban interstates completed.

Oddities:
The state highway maps designated both 2 and 4 lane roads as interstate highways from 1961 on. So a single corridor could have sections of 2 lane which were designated by the US route, other sections of 2 lane designated as interstate, and 4 lane sections designated as interstate. In some cases these 2 lane routes were on the alignment of the final interstate and may have been one of the eventual set of lanes.

One peculiar exception to the urban areas being connected by interstate was Butte which did not have a 4 lane I-15 north to Helena until very late in the game. A 2 lane I-15 was constructed earlier on and was eventually converted to a full 4 lanes. This I-15 segment was constructed on a significantly different alignment from US-91 to avoid interfering with the expansion of the Berkeley Pit mine. The long delay in upgrading I-15 was likely influenced by uncertainty in the final alignment as a result of the mining in the vicinity. It's also very possible that ACM discouraged the state from building the full I-15 at the time I-90 was completed over Homestake for this reason.