AARoads Forum

The Federal-Aid Highway Act of 1956 triggered a veritable avalanche of 90 percent federal funding for new controlled-access highways across the US. Which post-1956 Interstates were built first in your state, which came later, and which came last? What influenced the order in which they were built? Preexisting freeways, turnpikes, and/or four-lane rural highways are the most obvious examples, but there may be others. Were any planned toll roads canceled in favor of free Interstates? Did any routing decision likely affect sequencing as well? What was the urban-rural balance like? Was the sequence seemingly more strategic in nature, with some entire corridors completed before others were started? Or more ad hoc, with shorter segments completed early where the needs were greatest? Were some segments designed and built to barely-adequate pre-1956 standards?

And, does the sequencing make sense to you, or do you think things should've been done differently? Were there any cases in which one state built an Interstate right up to the state line and it wasn't connected to the other state's section for entirely too long? If so, which state should've built theirs earlier or later?

Please discuss.

If this thread is successful, it'll likely veer off topic, but I'm gonna start it off right by posting about my own state of Georgia even though I find most of the neighboring states more interesting.

Georgia

Pre-Interstate factors: Next to none: just two short sections of four-lane near Atlanta plus the early Atlanta expressways. Practically a blank slate, even compared to its neighboring states.

Strategic vs. incremental: Somewhat strategic, with the early start on I-75 in southern Georgia, the expeditious construction of I-85 north of Atlanta due to it not being in an established corridor, and, arguably, the early completion of Atlanta's urban Interstates. The rest was incremental and mostly sensible, though.

Urban vs. rural: Yeah, urban sections definitely had priority. In addition to what I've already mentioned, all the state's urban and suburban Interstates except I-75 in Macon were open by 1970.

Anomalies and WTFs:

In the mid sixties, Georgia built an isolated 25-mile stretch of I-16 (https://www.aaroads.com/forum/index.php?topic=32322.msg2557797;topicseen#msg2557797) for no obvious reason except that it was near where the state highway commissioner at the time lived.

Georgia reached the Alabama state line with I-20 four years after Alabama did, which, rightly or wrongly, I blame on Georgia. I think there were lesser mismatches with I-59 and I-85, but no issues with the other Interstates.

I-95 was built from the middle out, presumably because Georgia wanted to get some of it done while trying to keep as much long-distance traffic as possible on US 301 to avoid dumping too much traffic onto US 17. The alternative would've been to build the whole thing in one throw as was done on a smaller scale with I-85 north of Atlanta.

On I-85 north of Atlanta, yes, the route chosen did affect sequencing

The first stretch of road that would become I-85 was the Lexington Bypass, but the first pieces of interstate built in North Carolina was I-40 in Haywood County and the East-West Expressway in Winston-Salem, so it was definitely incremental.

We did freeways in Kansas (not just Interstates) about ten years ago:

Freeway completion dates in Kansas (https://www.aaroads.com/forum/index.php?topic=10097.0)

In the 1950's and early 1960's the biggest controversy, which resulted in I-35W (now I-135) being built, involved the possible cancellation of what is now free I-35 between Emporia and Ottawa.  In the 1960's, Manhattan also lobbied unsuccessfully to have I-70 follow US 24 rather than US 40 west of Topeka.  In the late 2000's/early 2010's, K-18 was expanded to full freeway, so in combination with K-177 Manhattan now has high-quality divided highway access to I-70 both west and east.

California

Pre-interstate factors: numerous corridors which were already being built that would be incorporated into the system:

Bay Area:
Southern Freeway (originally built as US 101, has been I-280 since 1968)
San Francisco Skyway/Eastshore Freeway (constructed in pieces as US 40, now I-80 - 1956-era designation)
Nimitz Freeway (originally built as Route 17, became I-880 in the 1980s, with a brief segment as I-680 in the early 1960s)
Macarthur Freeway (was this already built as US 50 before the I-5W designation was added in the early 1960s?)
segments of the Junipero Serra Freeway and Doyle Drive in SF that predate the planned I-280 and I-480 designations there
Central Freeway (corridor to post-2005 extent constructed by 1954; was part of the 1956-1965 planned Interstate 80 to Golden Gate Park)

Los Angeles area:
Santa Ana Freeway (planned and originally built entirely as US 101, mostly got incorporated into I-5)
Golden State Freeway (planned and partially built as US 6/99, now all I-5)
San Bernardino Freeway (was already finished by the mid-1950s as US 60/70/99, incorporated into I-10)
San Diego Freeway north of Irvine (partially built as Route 7, now entirely I-405)


Sacramento:
Roseville Freeway and North Sacramento Freeway (built as US 40/99W, incorporated as I-80 in the 1960s, partially still on I-80 corridor post-1982)

San Diego:
Montgomery Freeway (built as US 101, now I-5)
US 80 on what would later become I-8

Strategic vs. incremental: California prioritized having new-terrain routes get funded by the Interstate program ASAP (the saga of US 99 vs. I-5 ca. 1958, or I-15 vs. US 395 ca. 1969-1974).  In the Bay Area this was notable with I-280 being completed south of San Francisco by the early 1970s, today's I-780 (as I-680) already being complete in the 1960s; other examples include I-880 (now I-80) in Sacramento, I-805 in San Diego, I-210 and I-605 near LA, etc.

After the freeway revolts of the 1960s, the system construction became notably much less, particularly after the completion of 105 in 1992.  (This is not the same as a full slowdown of freeway building - but this involved state routes (99, 85, the Orange County toll roads) and portions of US 101 between LA and San Francisco)

Urban vs. rural: IIRC the West Side I-5 routing took about a decade to build out between the 1960s and 1970s, notably with the already-existing Route 99 (former US 50/99) freeway between Lodi and Sacramento as TEMP I-5.  (That freeway was part of the pre-1957 I-5 before the corridor switch). Wasn't I-40 east of Barstow finished by the 1970s?

For comparison with urban interstates:

I-480 between the Presidio and Broadway in SF, the portion of I-80 west of US 101, and the portion of I-280 north of Font Boulevard are all interstates that got halted for good by San Francisco's freeway revolt, with the 80 extension to Golden Gate Park being the most controversial.  In the East Bay, 80, 680, and 580 (former 5W) were all built out, with 880 and the 580 extension and 238 as eventual additions.

In San Mateo County, 380 west of 280 was canceled (though not sure if that was ever part of the interstate routing).  380 itself did not exist until the state applied for interstate funds for the airport spur freeway ca. 1968, which was originally State Route 186 in planning stages.

San Jose area pretty much had full buildout of Interstate miles, the notable change being 680 taking over a Milpitas bypass that was at one point (1963-1965) part of Route 17 in planning.

In LA, the main changes:

- 110/105 as paper designations removed from the San Bernardino and Santa Ana spurs into downtown.  Never signed.
- Creation of 110 (from 1934-1981 Route 11) and 710 (from 1964-1984 Route 7) out of existing freeways
- 1968-present 105 eventually being finished, after delays and lawsuits, in 1992.  I don't think I have actually ever seen a planning map showing 105 ending at 5, only at 605 (even though the proposed 42 freeway that 105 replaced would have incorporated a crossing to follow today's Route 90 in Orange County).
- I-210 being removed (not by FHWA but by CalTrans route numbering) along today's 57 between San Dimas and 10/71

San Diego area:
I-8 extended west of I-5 in the early 70s
Creation of 905 designation (still not interstate after all these years)
Routing of I-15 along 1964-1968 Route 103 to Barrio Logan/City Heights rather than on pre-1969 US 395 (now Route 163) into downtown San Diego.  The portion south of I-8 still not designated as Interstate even though it has been approved as part of the route.

Florida Yes, I'm breaking my own rule. Sorry. Also, I haven't delved into the minutia of the mop-up operations of the seventies because the early years were so fascinating. My observations here come largely from the 1962 and 1964 Rand McNally road atlases that I took delivery of last year.

Pre-Interstate factors: By 1962 and perhaps well before, almost all of US 1 had been four-laned all the way from Miami to the Georgia state line, and the Sunshine State Parkway, now Florida's Turnpike, had been opened from the Golden Glades Interchange to Fort Pierce. This was hugely important since it freed the state of most of the near-term need to build I-95. US 92 had been four-laned from Kissimmee through Orlando to Daytona Beach, as had US 441 most of the way from Orlando to Ocala, but those sections ended up being of little consequence to the matter at hand, as we'lll soon see.

It's not pre-Interstate but... after the Federal Highway Act of 1956 was passed, the planned extension of the Sunshine State Parkway along the Atlantic coast (or maybe inland near the St. Johns River, but still headed to Jacksonville) was canceled, but apparently the political will and organizational infrastructure for further turnpike construction was still very much intact, which likely influenced the events to follow.

Strategic vs. incremental: Florida was very strategic. Freed from the immediate need to build the bulk of I-95, Florida was able to concentrate on three priority corridors plus a few key urban sections. The most important was I-4, which by 1962 was complete west of Orlando and mostly under construction everywhere else. The central portions of I-95 in Jacksonville and I-10 westward of there were complete by 1960 (https://www.historicaerials.com/location/30.324256199611998/-81.68135405100091/1960/13), and I-95 was being extended incrementally in central Miami.

Additionally, in 1959, Governor LeRoy Collins proposed an extension of the turnpike to meet I-75 at Wildwood. Per my 1962 Rand McNally, the route for this extension was fully defined even though no credible route for I-75 was shown as yet. I-75 was under construction from US 41 south of Lake City to Georgia, which had already completed a substantial portion of I-75 itself. Also, I-10 was complete or under construction all the way to I-75.

My first glance at my 1964 Rand McNally map of Florida astonished me. By then, Florida's Turnpike was complete along with all of I-75 north of there-- and none south toward Tampa. Yep, I guess there were signs approaching the FL 44 interchange saying that FL 44 was the last free exit!

By 1964, it was possible to drive continuously on controlled-access highways from Wisconsin Dells to the northeastern end of the Connecticut Turnpike via the Pennsylvania and New Jersey Turnpikes, a distance of 1196 miles. Also, from Cleveland to the near end of Cape Cod, 703 miles, or to Gloucester, MA, at the end of MA 128, 671 miles. At 540 miles, Miami to the temporary end of I-75 at Unadilla was the next-longest such stretch in the country.

Quote from: An aside:I'd long wondered why Georgia had started its rural Interstate construction with an isolated section of I-75 in the far south rather than counting on long-distance traffic to and from Florida filtering through the state on several US highways. After my epiphany on this, it occurred to me that Florida might've communicated to Georgia its intent to develop the US 41 corridor as the main axis of travel between Florida and the Midwest, and that Georgia was thus prepared to accommodate the Floridian onslaught when the 90-10 Interstate money started rolling in. That might be an interesting topic for someone other than me to research if it hasn't been done already.

Despite Georgia's early start, though, I-75 didn't make it to Atlanta until 1970.

Tempering my enthusiasm somewhat, the 1964 Florida state map doesn't show I-75 open between Wildwood and Lake City. Maybe Rand McNally jumped the gun. Their maps have a lot of mistakes. There was no 1965 state map on FDOT's website, and the 1966 map shows I-75 complete north of the northern outskirts of Tampa. Still, a 1962-65 timeframe for this huge expansion would be pretty impressive, too.
https://www.fdot.gov/gis/floridatransportationmaparchive.shtm

Oh: By 1962, there was a bit of construction on I-10 and I-110 at Pensacola, but even in 1967, it still didn't provide a US 90 bypass of the city, and there was no other work on I-10. Instead, both I-75 north of I-4 and I-95 from I-4 to Jacksonville were completed, along with i-95 from Melbourne to Titusville and from Miami to Fort Lauderdale. By 1970, I-10 had had its breakout, being complete from Alabama to FL 285 and from Live Oak to I-75.

I'm not gonna research later than that.  :bigass:

Urban vs. rural: I'd say Florida did well at keeping its cities from becoming bottlenecks. Jacksonville was especially impressive in that regard.

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.

West Virginia

Growing up watching much of the construction of the Interstate system in West Virginia, it seemed like a hodge-podge to me at the time.  Looking back with a long monocular, now it looks like a well-planned major league construction project.  See what you think.

Pre-Interstate Factors

• Two-lane West Virginia Turnpike (about 88 miles of Super Two, completed in 1954)
• Fort Henry Bridge from Wheeling Island over the East Channel of the Ohio River (less than 1 mile, completed in 1955)
• Kanawha Boulevard East just west of the north end of the West Virginia Turnpike (about 1.25 miles of fourlane expressway completed about 1941)

Strategic Approach (Easy Pieces, if there really is such a thing in West Virginia)

• Construct the easiest city bypasses first: Huntington (1965); Parkersburg (1966); St. Albans (1966); Fairmont (1968); Morgantown (1973); Clarksburg (1974)
• Stretch out the network towards Charleston:  I-64 from Kentucky (1960-66); I-77 from Ohio (1961-73); I-79 from Pennsylvania (1967-1977); I-64 from Virginia (1971-73)
• Those other little guys:  I-81 across the Eastern Panhandle (1963-66); I-70 across the Northern Panhandle (1967-71); I-470 bypassing Wheeling (1981-83)

Strategic Approach (The Really, Truly Hard Pieces)

• Connect the puzzle together in Charleston: I-64 (1974-75); I-77 (1975); I-79 (1979)
• Rebuild the West Virginia Turnpike (1979-1986) and construct the Memorial Tunnel/Old Bender Bridge Bypass (1987)
• Build the I-64 East shortcut to the West Virginia Turnpike (1988)

Anomalies and Challenges

• The State Road Commission completed the first five miles of I-81 by 1963; it sat vacant until Virginia Department of Highways completed their section in 1965.
• Against the wishes of the FHWA, the State Road Commission decided to take the shortest route across the Northern Panhandle and squeezed the Wheeling Tunnel into I-70.  Nowadays, it's a literal squeeze.
• West Virginia opened up a few Super Two highways for a short time: I-79 from Star City -to- Pennsylvania (1974) and I-70 bypassing Elm City a tad more than a mile (1971).
• The WVDOH constructed the I-470 Vietnam Veterans Memorial Bridge just in time (the adjacent interchange with WV-2/US-250 is the largest interchange in the state).  But ODOT hadn't completed the interchange with OH-7 yet.
• The preferred routing of I-64/I-77 through Kanawha City was deemed too expensive; routing it through Charleston resulted in the need to construct an exit with another twin span across the Kanawha River to connect Kanawha City to [downtown].
• The western end of Corridor E was completed before the I-79 bridge across the Monongahela River; so for a short time in 1973 all I-79 traffic exited onto an incomplete US-48.  Which is now I-68.
• There was a nationwide uproar about the routing of I-64/I-77 through the impoverished Triangle Warehouse District in Charleston, going all the way to the United States Supreme Court.
• The only tunnel on the West Virginia Turnpike got bypassed. It is still used by FEMA as an underground training center for subway safety guys like me.
• The I-64 East Shortcut from Sam Black Church over to the Turnpike resulted in long stretch that was under construction for nearly 10 years that couldn't open until fully completed...
• ...and it came with a low level crossing of the New River and a high level crossing of the Glade Creek Gorge (the tallest bridge on the entire Interstate system).

Urban versus Rural

• Didn't really apply in West Virginia.  We tried to plow through Wheeling and Charleston about the same time that we were plowing through the Mountains.

Oregon was the first state in the west to complete I-5.  The freeway was done in 1965.  It was a real point of pride back then! 

Rick

Utah was highly incremental in its interstate construction, with different pieces opening up all over the place at seemingly random times.

The very first piece of interstate to open up was I-15 from Salt Lake City north through Bountiful in 1960. The Salt Lake segment was born out of an existing proposal for a US 91 downtown bypass that hadn't quite gotten off the ground before interstate funding came along. The north end of that segment tied into an existing US 89/91 expressway that had been built maybe a decade before. At the time, Salt Lake north to Ogden was the most important corridor in Utah (the southern SLC suburbs and Provo hadn't grown much then), so that first interstate segment was exactly where it was needed.

Over the next 15 or so years, various segments of interstate were completed at about the same rate in both urban and rural areas (with exception for I-70 - more below). I-84, then still numbered 80N, was done by 1975. Exceptions to the general pattern existed, though:

I-15 did not get a bypass of Nephi until the mid-1980s, and when it did, it followed a different route than what had been proposed earlier. This meant that the actual mileage was off from what had been used to number the exits north of there, and so all the exits on I-15 through the Wasatch Front up to Idaho wound up with numbers 3-4 higher than the centerline route mileage. Those exits were not renumbered until 2004 or 2005.

The last section of I-80 to be completed was actually an urban section - between roughly the Salt Lake airport and Redwood Rd. Incidentally, this was the last segment of any part of I-80 across the country to be finished, and marked the completion of the first transcontinental interstate.

Two segments of I-215 in Salt Lake amounting to about half the mileage were not built until the late 1980s. The few miles on either side of the western I-80 interchange opened a couple years after I-80 itself did, as part of the same big construction project. The southeast quadrant wasn't finished until 1989, but it likely would have been completed much sooner had it not been tied up in litigation and reroutings for several years.

The part of I-15 between the I-84 split at Tremonton and the Idaho line did not open until 1990. This is why even today, the northbound control city on a significant portion of signs towards the north end of that concurrency remains only "Snowville" - a little town on 84 almost 40 miles past where 15 splits off.

I-70 west of Green River was really in a class all its own, because it was not useful to the vast majority of Utah's population and followed an alignment the state hadn't wanted to begin with. Plus there was no preexisting corridor at all over the San Rafael Swell between Fremont Jct (SR 10) and Green River (US 6). A two-lane highway was open across the Swell by 1970 and soon became a realigned US 50, but interstate construction west of Green River really didn't get going for several more years. Green River and the Sevier Valley weren't bypassed until the late 1980s, and the Swell four-lane was finished in 1990 as the last interstate mileage in Utah.

Interesting that the last segment of I-80 was reconstructed as part of the I-80/I-215 interchange upgrade in the late 1980s/early 1990s.

Washington began upgrading US 99 a few years before the Act, so I-5 already had a few bypasses and expressway sections by the time it was designated. These weren't signed for a few more years, but in the meantime most of the rural sections were finished. Seattle's sections gradually opened between 1962 and 1967, while the last gap (between Everett and Marysville) was filled in 1969.

I-90 took much longer, with only the early Snoqualmie Pass, Moses Lake, and Spokane Valley sections done in the 1950s. Spokane's downtown viaduct was finished in 1969, and most of the Eastern Washington sections wrapped up around 1973. The Eastside sections between Bellevue and North Bend were opened between 1970 and 1978, and the final few miles to reach Seattle weren't fully complete until 1993.

I-82 started with the Yakima bypass in 1963 and was followed by the Manatash Ridge crossing in 1971. It was extended through the Yakima Valley by 1982 and the remaining section in and around the Tri-Cities (and into Oregon) took until 1988 due to squabbling over the routing.

Illinois All our map are online . WIU has most of the annual reports of IDOT  and separate reports on just the Interstate system . Those have not been digitized unfortunately because they included every detail fora roadvgeek. The first state maps showed up In The late 1940s.

Alabama, breaking my own rule again. Sorry, but it's too interesting to let it not get done.

Pre-Interstate factors: US 31 was four lanes from about twenty miles south of Birmingham to the Tennessee line except for a twenty-mile gap through the mountains north of Birmingham, and there were four-lane stretches on US 11 southward from Birmingham to the AL 5 split and on US 78 eastward to Leeds. There were also short sections of US 90 near Mobile, including the causeway across Mobile Bay, and the US 31-82 concurrency north of Montgomery. However, there were substantial four-lane stretches outside the Interstate corridors, and work continued on them and others even while Interstate construction was in full swing. In fact, today I learned that the 1958 state map (https://digital.archives.alabama.gov/digital/collection/maps/id/180/rec/24) showed five (!) new two-lane highways under construction north of I-20, including AL 53 connecting Huntsville to future I-65.

Urban vs. rural: Rural, with a caveat: While Alabama is known for the tardiness of its urban Interstate construction, great effort was put into connecting Birmingham and Montgomery to the north and northeast.

Strategic vs. incremental: A bit of both, actually. To me, it appears that the initial goal of the Interstate program was to provide four-lane corridors from Montgomery toward Nashville, Tuscaloosa toward Chattanooga, and Montgomery toward Atlanta, with Interstate construction deferred where four lanes already existed. By 1962, due to about 82 miles of new Interstate, the US 31-I-65 corridor had already been completed thusly except for that pesky ten miles north of Prattville, which IMO was pretty impressive. Also impressive was I-59 being under construction from Argo, 25 miles north of Birmingham, to the Georgia state line by 1964. However, the full network I described wasn't open until the 1967-68 map, by which time a few segments of I-10 west of Mobile, I-20 east of Birmingham, and I-65 on both sides of the Mobile River were open. 

I-65 Mobile-Montgomery was a tougher nut to crack, but its initial 56-mile segment, also completed in 1963, rounds out my personal trifecta of noteworthy early accomplishments. That segment, from AL 21 near Atmore to AL 106 at Georgiana, bypassed the most indirect sections of US 31, making it possible to build the rest incrementally. My 1964 Rand McNally looks rather bizarre there, with that lengthy section of I-65 complete and nothing else under construction in that corridor.

I'm not going into detail, but the rest of the original (pre-I-565) rural Interstates were open on the 1977-78 map except for the costly Dolly Parton Bridges on I-65, the George Wallace Tunnel and the new Mobile Bay causeway on I-10, and a random 16 miles of I-59-20. The core of Birmingham's freeway system was completed by the early seventies, but the extremities and all of I-459 were still not underway as of 1977-78. Oh: In Montgomery, I-85 and I-65 south of the river were open by 1973, but the closing link across the river toward Birmingham wasn't done until 1975.

Anomalies and WTFs: Of course, the greatest of these is the tardiness of urban freeway construction, which was very much at odds with practice in most other states. Beyond that, those initial segments of I-65, I-59, and I-85 reached the state lines significantly before the neighboring states' construction did. The worst was I-59, which Alabama completed by 1964 but Georgia didn't connect to until 1971. At least the amount of useless pavement there was small, unlike the four-year mismatch on I-20, which involved ten miles of highway.

Here's Connecticut. I included only openings of new freeway that successfully became sections of signed interstate, and designations of signed interstate. (this omits widening, reconstruction, cancellations, etc.)

1943: Gold Star Bridge opens, New London-Groton. This became part of I-95.

1945: Riverfront Boulevard opens in Hartford; this became part of the Conland-Whitehead Highway and is now part of I-91.

1948: Wilbur Cross Highway opens from US 5 to US 6/44 in Manchester. Now part of I-84.

1950: North Meadows Highway opens from Morgan Street, Hartford, to US 5A (now 159), Windsor. Now part of I-91.

1953: Darien Bypass (US 1) opens; now part of I-95.

1957: Bissell Bridge opens. Now part of I-291.

1958: Connecticut Turnpike opens. Now part of I-95 and I-395. I-95 starts appearing on maps.

1950s: Waterbury Expressway opens, from Union Street to Hamilton Avenue. Now part of I-84.

1961: first I-91 signs are posted north of Hartford. First new sections of I-84 open, in Danbury and Waterbury.

1962: Route 52 extended to Route 101. Now part of I-395.

1963: I-84 opens between Housatonic River and Waterbury.

1964: I-95 opens from East Lyme to RI state line. I-95 is complete.

1965: I-84 opens in West Hartford; I-91 opens from Meriden to Hartford.

1966: I-91 opens from New Haven to Meriden. I-91 is complete.

1967: I-84 through the Route 8 interchange is open.

1968: Route 52 is completed to the MA state line. I-87 opens in Greenwich. (yes, I-87 (https://www.kurumi.com/roads/ct/i87.html))

1969: I-84 opens from Plainville to Farmington. I-84 is complete.

1970: I-87 becomes I-684.

1971: I-84 (now I-384) opens in Manchester and Bolton. Route 66 (now I-691) opens in Meriden. I-84 opens in Willimantic.

1983: I-395 designated.

1984: I-384 designated. I-84 in Willimantic is demoted.

1992: I-291 is complete.

The sequencing seemed primarily as-needed, though there was a strategy in place since the 1940s for the three primary interstates to be eventually completed. The CT Turnpike was a toll road until 1985.

Anomalies: many. I-87/684. I-86/84/384. The fact that I-284/484 really existed (in part) for a while, but unsigned. I-395 was originally to be I-290. I-84 was in 3 disconnected segments into the 1980s. Just Connecticut stuff :-)

I mentioned the staging in Illinois
Pre Interstate. A lot of planning . Illinois has its Interstate map invite annual highway report in 1947. 55 the Route 66 is under construction for 4 lanes .Some had to be reconstructed. Illinois has always tried to get the most federal funds.
All the Interstate were built with the exception of the 494 crosstown expressway. 155 miles were built as tollways in 1959 The Tri State and Northwest.
Illinois built almost 500 miles more over its original sytem. Some was chargeable.
Urban Rural. While Urban started first there is no doubt downstate did very well. Almost all the additional roads in metro Chicago are toll . Most of downstate is freeway.

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. 

Pre-Interstate factors: Baltimore-Washington Parkway, Washington National Pike (US 240) Frederick Freeway, and the planning and design stages of the Harbor Tunnel Thruway.

Strategic vs. incremental: Incremental, with the possible exception of I-95 north of Baltimore. I-70N and S and I-81 were the first to get underway in the state before 1960, when the Frederick Freeway was converted from US 40 and the Hagerstown Bypass was built to replace US 11. The conversion of US 240 to I-70S (now I-270) came shortly afterward. Next came the upgrade of US 111 to I-83 north of Baltimore. I-95 opened north of Baltimore in 1963, tying in with the north end of the Harbor Tunnel Thruway in east Baltimore, and from the Capital Beltway to southwest Baltimore sometime around 1970; it was of course cancelled through and just north of DC. The HBT became I-895 around 1980. I-95 was finally completed within Baltimore in 1985, when the Fort McHenry Tunnel opened.

The Baltimore Beltway (I-695) also began construction before 1960 and was eventually completed when the Key Bridge opened in 1977. I-795 was built by 1983 parallel to MD 140 northwest of Baltimore; I-370 came in the late-1980s, around the same time MD 46 between UMBC and the BWI airport was expanded and re-designated as I-195.

There were then additions to Maryland's original system plans: I-68 at the turn of the 1990s, when the National Freeway was built in replacement of the original path of US 40 through western Maryland, and I-97 as an upgrade of part of MD 3 between Annapolis and the Harbor Tunnel at the same time, followed by the upgrade of US 50 from just east of DC (at the Capital Beltway) to Annapolis to the hidden I-595 (which was originally the corridor with the I-68 designation).

Urban vs. rural: Rural by a wide margin. Again, tons of freeway opposition in DC and Baltimore.

Anomalies and WTFs: Despite tolls being removed on most of I-95 north of Baltimore, its two median service plazas remain. I-70 ends in a parking lot and I-83 at a traffic light in Baltimore due to the freeway revolts. Both the Woodrow Wilson Bridge on the Capital Beltway and the Curtis Creek bridge on 695 near the Key Bridge are drawbridges. I-97 is contained within a single county.

South Carolina , breaking my own rule again and more or less daring/inviting Mapmikey to correct me. :) I really wish I'd started this thread before bridgereports.com went down, especially since I can't find archived SC official state maps online. I'm doing this mainly from memory plus my 1962 and 64 Rand McNallys.

Pre-Interstate factors: The biggest was the early-fifties construction of a relocated two-lane US 29 incorporating SC 129 at Lyman, what's now Business 85 through Spartanburg, and running I guess to the NC state line (it's visible on the 1955 historicaerial (Twitter link) (https://www.historicaerials.com/location/35.097186994774475/-81.62713682628548/1955/14) as far as Gaffney and doesn't end there). There must've been a great effort to upgrade most of this highway to Interstate standards before ROW became prohibitively expensive. Beyond that, US 29 was four lanes from what's now the US 29 Anderson split to Spartanburg. While the southernmost portion of this highway was an expressway that was incorporated into I-85 and I-185, the rest was bypassed by new 85 by 1962, and the metamorphosis of new US 29 into I-85 to the NC line was complete by 1962 as well.

Also, US 76 had been four-laned from Columbia to Sumter by 1957 per historicaerials, including Sumter's impressive freeway bypass. This enabled SC to defer construction of I-20 east of Columbia while maintaining a decent connection from that city to the I-95 corridor.

Urban vs. rural: SC doesn't really have urban Interstates, though the spurs into the various cities were built early on.

Strategic vs. incremental: Very strategic. In addition to the I-85 corridor described above, the first phase of Interstate construction consisted of the triangle connecting Greenville, Spartanburg, and Columbia, comprising much of I-26 and the portion of US 276 that eventually became I-385. Due to their very conservative design, I suspect these highways were under development before the Interstate era. These sections of I-26 plus extensions northward almost to the NC state line and eastward to Orangeburg were open by 1962. By 1964, I-26 had made it almost to Charleston, the initial I-385 was open, and the tie to I-85 in Georgia was under construction. The initial US 1 bypass section of I-20 at Columbia had started construction, too, which...

One other strategic factor had to do with the macro-level routing of I-20. Before I-20 was built, the best route between Columbia and Atlanta was via US 378 and  US 78, completely outside the US 1-I-20 corridor. Also, US 301, not US 1, had long since become the major Florida-New York corridor. This enabled most of I-20 to be deferred until Georgia had completed enough of I-20 to make Atl-Augusta-Cola an attractive option.

Speaking of US 301, sometime after 1964, SC four-laned its section from the Georgia state line to I-95. As I mention in my Georgia post, there was an understandable desire not to dump I-95-level traffic onto inadequate two-lane US 17 and US 15 until I-95 was largely open. SC put their money where their desires were much more convincingly than Georgia did.

While we're talking strategy, I'll mention that I-77 wasn't even on the menu until the rest of the Interstates had been completed. I wonder if it would've taken any sort of priority had it been in the interstate system from day one.

Bearing all this in mind, the next obvious priority was I-95 working southward from the NC line to the four-laned US 301 at Santee and slightly further to I-26 for the connection to Charleston. I'm hazy on exactly what happened next, but it was basically incremental work on the remaining sections of I-20 and I-95. They finished the closing link of I-20 between Columbia and Augusta before Georgia had finished Atl-Augusta. I also recall that I-20 east of Columbia stopped at Camden for several years, making it essentially an augmentation of US 1 rather than an attractive route to I-95 at Florence. I-20 east of Camden might've been the last section of original Interstate completed in SC. Pathetically, I had to consult the 1972 official Georgia map (https://www.dot.ga.gov/DriveSmart/MapsData/Documents/HwyAndTransportationMaps/1972.pdf), which shows huge sections of I-95 under construction in both states, with only the bridge over the Savannah River not yet underway. It wasn't feasible to build the entire thing at once, but they came pretty close. I'm impressed.

Anomalies and WTFs: Not much. The only thing I found that was slightly questionable was the completion of I-26 west of I-85 so early. 

^^^
Might be a bit fuzzy on this one, but I vaguely remember when I-77 ended at Mitford (Old Exit 32, now Exit 48 Winnsboro/Great Falls) and SCDOT recommended using SC-200 and US-321 to get to Columbia (rather than a shorter route through Mitford to US-21, which didn't have much leftover traffic after the northern portion of I-77 was complete).  Although there was some backtracking to get over to US-21, it didn't make any sense to get slogged down through Winnsboro when US-21 was so much faster (long before Blythewood got built up).

North Carolina

It's hard to get my hands around the development of the Interstate System here in North Carolina, even though I grew up travelling alongside many of these routes as they were constructed.  My first notion is that North Carolina was so long to traverse east-to-west that any logical construction pattern would have been considered unfair to some.  But I-40 ended in Greensboro, just a hair beyond the halfway point of today's 424-mile route; and I-85 cuts a diagonal through the midsection that is mere 235 miles long.

It's taken nearly 6 weeks to parse through the hoards of data and I'm still not sure that I can make sense of all of it.  See what you think:

Pre-Existing Factors, Part One

North Carolina was a relatively poor Southern state at the beginning of the development of the Interstate system, and as such didn't have much in the way of fourlane highways prior to the arrival of these modern freeways.  Only one of these sections actually preceded the construction of the Interstate Highway System, but they factored into the puzzle.

• US-29/US-70:  A new fourlane highway between the Yadkin River —and- Greensboro was completed by 1957.  Almost all of this was converted to a freeway during the 1960s and early 1970s.  Several smaller sections became part of I-85, but the bulk of this became TEMP I-85.
  
  
• US-158/US-421:  The eastern section of what is now know as the Salem Parkway was completed in 1958.
  
  
• US-70:  The famed ascent up the Blue Ridge front up to Black Mountain was fully converted to a freeway in 1960.  About the same time, a new Super Two was completed between Greensboro —and- (then) Hillsboro (this piece appears to have been constructed under the auspices of I-85, but I can't find evidence thereof).
  
  
• US-301:  A new short section of fourlane highway was completed between Kenly —and- Wilson in 1958.  A little further up, a fourlane bypass was completed around Elm City in 1961.  These get connected along with a new fourlane bypass of Rocky Mount in 1967.  This is connected to the new section of I-95 north of there with a fourlane connector that eventually becomes part of NC-4.  Eventually, this all becomes Green I-95 Business (now decommissioned).

Logical Construction

• I-85 bypassing Charlotte (1957-1960)
• I-40 and I-85 bypassing Greensboro (1959)
• I-40 Winston-Salem —to— Greensboro (1959-60; 1963)
• I-85 Charlotte —to— Spencer (1959-1960; 1970-1971)
• I-85 Greensboro —to— (then) Hillsboro (1959)
• I-40 bypassing Winston-Salem (1960)
• I-85  South Carolina —to— Charlotte (1960-1964)
• I-85 (then) Hillsboro —to— Durham (1960)
• I-40 Tennessee Line —to— Asheville (1963; 1967; 1970; 1973)
• I-40 bypassing Asheville (1966-1968; 1971-1973)
• I-95 South Carolina —to- Fayetteville (1959-1962; 1972)
• I-95 Rocky Mount —to- Virginia (1963; 1967)
• I-26 leading up into Asheville (1969)
• I-77 South Carolina —to- Charlotte (1970)
• I-77 bypassing Charlotte (1970)

Disorganized (Hit-or-Miss) Construction

• I-95 Fayetteville —to- Rocky Mount (1958-1959; 1978)
• I-40 Asheville  —to— Statesville (1959-61; 1971-1973; 1979)
• I-40 Statesville  —to— Winston-Salem (1959-1960; 1969-1970)
• I-85 Durham —to— Virginia (1960; 1965; 1970-1971)
• I-77 Charlotte —to- Statesville (1967; 1971; 1976-1977)
• I-77 Statesville —to- Virginia (1967; 1976-1977)
• I-26 South Carolina —to- Asheville (1966-1969; 1973-1976)

Leftovers

• I-95 bypassing Wilson and Rocky Mount (1978)
• I-95 bypassing Fayetteville (1980)
• I-85 Spencer —to— Greensboro (1985)

Pre-Existing Factors, Part Deux

The (then) North Carolina Highway Commission (NCHC) constructed a new freeway between Raleigh —and- Durham.  The earliest sections became the unnumbered Wade Avenue Freeway in Raleigh and the (then) unnumbered Durham Freeway were completed in 1971.  The remainder connecting those pieces was completed in 1974, which by then had been approved as part of the extended I-40 corridor.  A portion of the Durham Freeway eventually became I-885.

Anomalies and Challenges

• I-77 was planned to cross into Virginia much further west than the current route north of Elkin, roughly parallel to US-21.  But Virginia wanted the route to parallel US-52, which comprised of an easier route across the interior Blue Ridge range.  VDOT ended up with a difficult route down from Fancy Gap, leaving NCHC with the easy part south of there.
  
  
• The freeway ascending the Blue Ridge front to Black Mountain remained posted as US-70 until finally redesignated as I-40 in 1981.  As best as I can tell, it never was fully compliant with Interstate standards and just simply got absorbed into the System.
  
  
• TEMP I-85 eventually got upgraded to a full freeway south of High Point by 1984, only one year prior to getting permanently bypassed by the "real"  I-85.  But alas, much of this route eventually became I-285.
  
  
• Through Winston-Salem, the original section of the old I-40 (now) Salem Parkway was suitable for expansion but the later section through downtown was simply too tight.  A complete bypass to the south was completed in late 1992, one of the few sections of the original Interstate system to become truly obsolete. 
  
  
• Talking about obsolete, the original section of I-85 in Greensboro got bypassed in 2005 and the original section of I-40 in Greensboro also got bypassed in 2008.  But due to public demand (actually political, but I digress), I-40 got pushed back onto Death Valley a mere seven months later.  The southern portion of the Greensboro Urban Loop that wasn't part of I-85 became I-73.  I-73 and I-85 overlap for about 1 mile, but they function as parallel freeways in the same corridor.  Coincidentally, it seems.
  
  
• Not only is North Carolina a fairly large state geographically, but the Aughts brought huge population growth and accordingly, huge expansion to the freeway network.  Since then, NCDOT has received a number of new Interstate highways:  I-74 (2000); I-840 (2002); I-295 (2005); I-140 (2008); I-795 (2009); I-495 (2014, decommissioned 2017); I-87 (2017, replacing I-495); I-785 (2017); I-840 (2018); I-285 (2018); I-885 (2022); I-587 (2002); I-42 (future); and I-685 (future).  Care to guess what the other one was?  Perhaps the most hated route on AARoads is I-73, which actually was posted before what some might call the Aught Naughts (in 1998).  Which leads us to the weirdest of all:
  
  
• The portion of the original I-73 posted north of the Greensboro Urban Loop was decommissioned in 2009 after I-73 was rerouted around Greensboro on the western portion of the loop.  As far as I can tell, this is the only section of freeway constructed during the Interstate era that (but not as part of the Interstate system) that has been decommisioned.

Urban versus Rural

• Charlotte, Greensboro, Durham and Winston-Salem certainly got favored over the rural sections, which was probably a necessity given the lack of fourlane highways in the Old North State.  Amazingly, Raleigh was left out of the original Interstate System.
  
  
• Smaller cities ended up waiting for near the end of the construction phasing:  Asheville (1973), Rocky Mount (1978), Fayetteville (1980) and High Point (1985).  But those areas were pushed along with fourlane highways that were constructed during the same time as rural portions of the Interstate were getting connected together.  Asheville ended up with I-240; the others ended up with the Green shields.

MN:

The first segment of Interstate to open was I-35 between Medford and Owatonna circa 1958. A section of I-35W between the Minnesota River and the Richfield/Minneapolis city line by 1960 came next.

By 1965:
A section of I-35 from Rush City to Sandstone was complete.
Virtually none of I-94 other than the Fergus Falls bypass had been built.
Two sections of I-494, one from TH 7 to the TH 5 airport split, and from the Wakota Bridge back to I-94 in Oakdale were open.
A section of I-694 between I-35W and I-35E was open.
A section of I-90 from the South Dakota border to east of Luverne was open, as was a section from east of Albert Lea to US 63.
A section of I-35E between I-694 and Maryland Avenue in St. Paul was open.
The plan was still for I-35 to follow US 69 rather than US 65 south of Albert Lea at this date.

By 1970:
-I-94 is still wholly unbuilt between Albany and MSP.except for the I-694 duplex. The section through the downtowns is largely finished as is a separate section between White Bear Avenue and I-494/694 on St. Paul's east side.
-I-694 is open from I-494 in Maple Grove to I-35E
-I-35W is largely complete except for its section through northeast Minneapolis.
-I-35E is largely unchanged from 1965 except for a section between then-TH 110 and TH 13 near St. Paul.
-I-494 is now open completely on the west side of MSP.
-I-35 is complete between the 35W/35E Forest Lake split and Cloquet to the north of MSP, and complete south of MSP between Burnsville and TH 251 north of Albert Lea. The plans to shift I-35 to follow US 65 south of Albert Lea are under construction. North of MSP, a section of I-35 in Duluth from Boundary Ave to Cody St is open. The section from 40th Ave West to 27th Ave West in Duluth is also done but unsure if traffic was allowed to use it at this time.
-A few more incremental sections of I-90 have opened, including from the Wisconsin border to the US 14/61 split west of La Crescent, a westward extension of the piece that terminated west of Austin in 1965 to TH 13 at Albert Lea, and the South Dakota-Luverne piece has been extended eastward to TH 60 at Worthington.
-I-535 is designated on the Blatnik Bridge in 1971, but the freeway between the bridge proper and I-35 is not complete.

By 1975:
-I-694 is complete.
-I-94 northwest of MSP is built to St. Augusta, where the gap runs from St. Augusta to Albany.
-I-35 north of MSP has a gap outside Duluth between today's Carlton CSAH 61 interchange at Exit 245 and Boundary Ave (Exit 249). This is where I-35 was largely built on top of the existing US 61 expressway rather than bypassing it like it does for the Esko-Cloquet section. I-35 is finished from Boundary Avenue to Mesaba Avenue in Duluth. South of MSP it is complete to the Iowa border.
-I-90's gap has shrunk to existing between TH 4 at Sherburn and TH 109 in Alden.
-I-35W still has a gap in northeast Minneapolis near the planned I-335 interchange. The ill-fated Mississippi River bridge has been open since the late 1960s by this time.
-I-35E is complete north of I-94. South of St. Paul, the section from TH 13 to TH 5/West 7th across the Mississippi is open. Still unbuilt in rural Dakota County at this time.
-I-535 is complete.

By 1980:
Not a lot has changed since 1975.
-I-94 is now finished through the tunnel between US 12 in Minneapolis and 494/694 in Oakdale, as well as fully open northwest of MSP with the St. Cloud-area gap now filled.
-I-90 is complete (there's a "golden spike" marker near Blue Earth)
-I-35's gaps in the Duluth area are filled.
-I-35E in Dakota County is still not open.
-I-335 is officially scrapped and I-35W is complete.

By 1985:
-I-35E between the I-35 Burnsville split and TH 77/Cedar Avenue is open.
-I-94 is complete through north Minneapolis, leaving just the route east of 494/694 to Wisconsin unfinished.
-I-494 is complete.

Between 1985 and 1987 (because of course 1985-1986 is the one fucking map the digital archives don't have):
-I-94 complete.
-I-35E is now complete from I-35W to Grand Avenue in St. Paul.

1988:
-Work begins on the I-35 tunnels in Duluth.

1991:
-I-394 designated.
-I-35E complete.

1992:
-I-35 Duluth extension to 26th Avenue East completed; I-35 complete.

Virginia

Pre-Interstate Factors

Prior to the development of the Interstate system, Virginia had an extension network of fourlane highways and fourlane roads, plus a few freeways.  Here are some that got incorporated into the Interstate system:

• Richmond-Petersburg Turnpike (1958)
• VA-350 Shirley Highway (1941-1952)
• US-60 Bypass Low Moor —to— Clifton Forge (1954)
• VA-168 Virginia Beach (1958)
• US-11/US-52 Wytheville —to— Fort Chiswell (fourlaned in 1958)

Strategic

• I-81 Staunton —to— West Virginia (1960, 1965-1969)
• I-81  Roanoke —to— Lexington (1960, 1964-1965)
• I-81  Tennessee —to— Wytheville (1962-1965)
• I-95  Richmond —to— Fredericksburg (1963-1964)
• I-85  North Carolina —to— Petersburg (1965, 1969-1970)
• I-95/I-64 through Richmond (1967)
• I-81/I-64  Lexington —to— Staunton (1967-1970)
• I-64  Charlottesville —to— Richmond (1967- 1970)
• I-64  Staunton —to— Charlottesville (1970-1971)
• I-77  Wytheville —to— East River Mountain Tunnel (1972-1975)
• I-81  Wytheville —to— Fort Chiswell (1985)

Disorganized

• I-95  North Carolina —to— Petersburg (1959-1963, 1980-1982)
• I-64  Hampton Roads —to— Bower Hill (1959, 1968-1969, 1973-1976)
• I-64  Richmond —to— Hampton Roads (1960, 1965-1967, 1972-1974, 1978)
• I-81  Fort Chiswell —to— Roanoke (1961, 1965, 1971, 1977)
• I-66  Strasburg —to— Fairfax (1962, 1964, 1971, 1977-1980)
• I-95  Fredericksburg —to— District of Columbia (1964, 1981-1982)
• I-64  West Virginia —to— Lexington (1964-1966, 1971, 1976-1979)
• I-77  North Carolina —to— Fort Chiswell (1977-1978, 1985)

Strategic but Politically Altered

• I-66  Fairfax —to— District of Columbia (1964, 1982)

Anomalies and Oddities

The route of the Shirley Highway (VA-350) constructed between 1941 and 1952 was approved as part of the original corridor for I-95.  However, the entirety of the Shirley Highway could not be renumbered as I-95 because of the existence of a railroad crossing at grade.  Beginning in 1965, the Virginia Department of Highways began the upgrade of the corridor to Interstate standards.  Upon the abandonment of the Washington and Old Dominion Railway in 1968, the Shirley Highway was renumbered as I-95.  Upgrades continued until 1975, which included the first reversible bus-only expressway (later becoming HOV lanes).

US-301 was upgraded to a fourlane highway between Emporia and VA-35 near Templeton in 1956 and 1957.  This section was parallel to the final portion of I-95 to be constructed in the Old Dominion.  The construction of I-95 was phased such that most of the northbound lanes of US-301 between Jarratt and VA-35 were upgraded to become the southbound lanes of I-95.

The East River Mountain Tunnel on I-77 connects Bland County, Virginia to Mercer County, West Virginia.  When it was completed in 1974, it was the sixth longest tunnel in the United States at 5,412 feet in length.  It is also the only mountain tunnel on the Interstate system that is truly interstate (connecting two different states).  It is one of only two mountain tunnels that carry roads across state lines, and of course that other one (Cumberland Gap Tunnel) is also in Virginia.  Virginia is also home to the two railroad tunnels that crossed state lines:  another one at Cumberland Gap and the C&O Alleghany Summit tunnels that roughly parallel I-64.

During the planning of I-66 between the Capital Beltway and Arlington, VDH (and later VDOT) ran into stiff political opposition.  When the Washington and Old Dominion Railroad called it quits in 1968, VDH mistakenly thought it would get a clear path to constructing the freeway inside the Beltway.  In perhaps the most famous of all of the worldwide Highway Revolts, opponents were able to get decisions by the Federal District Court and oddly, the Secretary of Transportation that eliminated the proposed eightlane I-66 freeway.  Eventually, the newly-renamed VDOT would settle for a fourlane freeway with provisions for the Metrorail Orange Line extension in the median of the portion of I-66 west of Ballston.

A portion of I-66 inside the Beltway was constructed on a converted railroad right-of-way.  Of course, there is also another section of the Interstate system in Virginia (I-195 Acca Freeway in Richmond) that was constructed on railroad right-of-way, but the railroad mainline remains in the median and is part of CSX busy north-south corridor (former Atlantic Coast Line).  I highly suspect that there are other Interstate highways built along railroad right-of-ways, but I couldn't find any.  Sounds like a topic for a new thread.

Urban versus Rural

Virginia seems to have a pretty good balance between development of urban and rural stretches of Interstate in the early days, with the urban stretches getting completed quicker simply because of the shorter lengths.

The first Interstate in Michigan was I-75 near the Ohio state line in 1957. The last to be completed was I-69 southwest of Lansing in 1992.

I-75 near OH might have been the first highway in MI built as an Interstate, but many portions of I-94 were built prior to that. As far back as WWII and even earlier.

It is interesting to note that portions of I-696 were both near the beginning of Interstate building in MI and the end of it. It took 26 years to complete.

Quote from: GaryV on July 06, 2023, 07:39:01 AM
I-75 near OH might have been the first highway in MI built as an Interstate, but many portions of I-94 were built prior to that. As far back as WWII and even earlier.

It is interesting to note that portions of I-696 were both near the beginning of Interstate building in MI and the end of it. It took 26 years to complete.

At that time I-94 was still US-12. It was the middle section of I-696 that made it take so long to complete. I remember the middle section not being there.

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.

Quote from: jp the roadgeek on June 11, 2023, 06:06:11 PM
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.

Quote from: Tom958 on May 21, 2023, 07:38:02 AM

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.

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.