The original Interstate system plan

[michiganguy123]

What made them create all interstates as 4+ lanes instead of 2?

[mgk920]

What made them create all interstates as 4+ lanes instead of 2?

Likely Eisenhower's experiences as a commanding general during WWII.

Mike

[vdeane]

What made them create all interstates as 4+ lanes instead of 2?

Likely Eisenhower's experiences as a commanding general during WWII.

Mike

Actually, a few actually did get built as 2 lanes initially, like I-95 north of Bangor.  Safety proved to be an issue, however.

[mgk920]

What made them create all interstates as 4+ lanes instead of 2?

Likely Eisenhower's experiences as a commanding general during WWII.

Mike

Actually, a few actually did get built as 2 lanes initially, like I-95 north of Bangor.  Safety proved to be an issue, however.

I-15 at the Idaho-Montana state line was also built as two lanes due to light traffic (that section was even in the Guinness book for many years as having the lowest AADT of any mainline interstate), but it has long since been upgraded to a conventional four lanes divided.

Mike

[SEWIGuy]

But now it seems as if not only is the interstate system not living up to the pedestal I put it on, but that it never did.

To further respond to this thought:

If the US route system's most egregious grid divegence is US 11...


IMO having I-43 and I-57 share the same direct north south trajectory but as two separate numbers (when IIRC 57 was once proposed to continue up 43) messed up the number assignments west of Chicago. This is how I-49 is entirely west of I-39!

(Not to mention the issues of using major numbers for intrastate 45 and short 30, especially when California had suggested using 30 instead of the eventual I-40 for the US 66 corridor)

I-45 being west of the northern half of I-35 was inevitably going to cause problems with the grid. There was no reason for the northern states to skip numbers under 45, since it's far enough away and Texas wasn't going to use them all. Make that I-39 from the start and the grid probably ends up much neater.

That and there should have been a Milwaukee-Green Bay interstate earlier on like Wisconsin wanted. If that highway opened earlier Illinois wouldn't have as much grounds to complain about extending 55 or 57 north to the border. (Hell, if 55 got extended there's a case for making I-41 a very long 3di.)

Good thing the grid is irrelevant and I-43 works just fine.

[Flint1979]

What I think is funny is how like I-43 is only about 200 miles or so west of I-75, even further I-75 is within 300 miles of I-39.

[pderocco]

What I think is funny is how like I-43 is only about 200 miles or so west of I-75, even further I-75 is within 300 miles of I-39.

Well, I-75 is pretty diagonal. US-6 should have ended up somewhere around Seattle by the numbers, but it originally ended up a hundred miles or so from US-80. But imagine what it would be like if we didn't have any major diagonal routes.

[TheStranger]

But imagine what it would be like if we didn't have any major diagonal routes.

The more subtle question from this:

I often bring up the concept of routing logic, but I think it does makes sense to think about this for a second: which diagonal routes do feel like one coheisve corridor vs. cobbled together without any real practical trajectory?

Example from the US route system: US 62 going from El Paso to Niagara Falls for something that is very much not a unified routing.

Example from the Interstate system that is super logical: I-71 (which to some degree parallels US 42), connecting Louisville and the three most important cities in Ohio on a cohesive pathway.  In fact, my friends and I took all of 71 as part of a 2006 trip to the Clevleand Grand Prix.

Another one that works really well for both the US and Interstate system is the parallel set of I-85 and US 29.

[Quillz]

What I think is funny is how like I-43 is only about 200 miles or so west of I-75, even further I-75 is within 300 miles of I-39.

Well, I-75 is pretty diagonal. US-6 should have ended up somewhere around Seattle by the numbers, but it originally ended up a hundred miles or so from US-80. But imagine what it would be like if we didn't have any major diagonal routes.

US-6 originally did not leave the Northeast. Its original extent was roughly Pennsylvania to Cape Cod. It was gradually extended in a diagonal pattern, and eventually it reached Long Beach. I'm not sure if this was just a series of happy accidents, or if at some point it was decided to make US-6 become the longest numbered route in the country (since taken over by US-20). 

It makes a little more sense when comparing it to some other US routes that are mainly diagonal, like US-52 and US-54. I believe US-62 is the super oddball that touches both Mexico and Canada despite being a west-east route.

I think a poster here mentioned once that what probably would have helped is if a range of numbers was specifically set aside for diagonal routes. It also would have helped is having a consistent logic for numbers: i.e. is a route's number determined by its terminus, or its rough location within the country? US-11's numbering makes sense if you consider its northern terminus, but its southern terminus is well out of alignment. Then you have something like US-30 which makes sense for most of its length, but it's effectively flipped in Oregon, being north of US-20 instead of south. (Although this is due to US-20 originally ending near Yellowstone).

[Flint1979]

What I think is funny is how like I-43 is only about 200 miles or so west of I-75, even further I-75 is within 300 miles of I-39.

Well, I-75 is pretty diagonal. US-6 should have ended up somewhere around Seattle by the numbers, but it originally ended up a hundred miles or so from US-80. But imagine what it would be like if we didn't have any major diagonal routes.

How do you figure that I-75 is diagonal? It pretty much goes north and south wherever it's at. US-6 is out of the grid just about everywhere.

[Flint1979]

But imagine what it would be like if we didn't have any major diagonal routes.

The more subtle question from this:

I often bring up the concept of routing logic, but I think it does makes sense to think about this for a second: which diagonal routes do feel like one coheisve corridor vs. cobbled together without any real practical trajectory?

Example from the US route system: US 62 going from El Paso to Niagara Falls for something that is very much not a unified routing.

Example from the Interstate system that is super logical: I-71 (which to some degree parallels US 42), connecting Louisville and the three most important cities in Ohio on a cohesive pathway.  In fact, my friends and I took all of 71 as part of a 2006 trip to the Clevleand Grand Prix.

Another one that works really well for both the US and Interstate system is the parallel set of I-85 and US 29.

The only thing that I-71 does that US-42 doesn't is I-71 goes through Columbus while US-42 bypasses it.

[vdeane]

or if at some point it was decided to make US-6 become the longest numbered route in the country (since taken over by US-20). 

Isn't that debatable based on whether or not US 20 is discontinuous through Yellowstone?

[PNWRoadgeek]

The question that I have is: Why are some US highways diagonal, while most interstates are mostly due north-south/east-west? The only really majorly diagonal Interstates are I-24, I-85, and I guess I-69 is kinda diagonal as well. Those are the ones I think of, unless I'm forgetting one. I assume it's because a straight pathway is better to intersect with major cities. Also, lots of the X0 and X1/5 US routes follow straight pathways.

[Life in Paradise]

What made them create all interstates as 4+ lanes instead of 2?

Likely Eisenhower's experiences as a commanding general during WWII.

Mike

Actually, a few actually did get built as 2 lanes initially, like I-95 north of Bangor.  Safety proved to be an issue, however.

I-15 at the Idaho-Montana state line was also built as two lanes due to light traffic (that section was even in the Guinness book for many years as having the lowest AADT of any mainline interstate), but it has long since been upgraded to a conventional four lanes divided.

Mike

A long stretch of I-70 in Utah was originally 2 lanes.  I remember taking a family trip out west and going through that area not too long after it was constructed in the early 70s.

[hotdogPi]

The question that I have is: Why are some US highways diagonal, while most interstates are mostly due north-south/east-west? The only really majorly diagonal Interstates are I-24, I-85, and I guess I-69 is kinda diagonal as well. Those are the ones I think of, unless I'm forgetting one. I assume it's because a straight pathway is better to intersect with major cities. Also, lots of the X0 and X1/5 US routes follow straight pathways.

4, 22, 30, 37, 44, 71, 81, western 84, 89

It's not just the three you mentioned.

[PNWRoadgeek]

The question that I have is: Why are some US highways diagonal, while most interstates are mostly due north-south/east-west? The only really majorly diagonal Interstates are I-24, I-85, and I guess I-69 is kinda diagonal as well. Those are the ones I think of, unless I'm forgetting one. I assume it's because a straight pathway is better to intersect with major cities. Also, lots of the X0 and X1/5 US routes follow straight pathways.

4, 22, 30, 37, 44, 71, 81, western 84, 89

It's not just the three you mentioned.

I forget lol. Must just be really tired today. To me though, 89, 30, and 4 aren't so northwest-southeast/southewest-northeast that they could be considered diagonal IMO. The rest I get.

[hotdogPi]

What do you mean I-4 isn't diagonal? It's about as close to 45° as you can get.

[JayhawkCO]

I-59 also pretty darn diagonal.

[PNWRoadgeek]

What do you mean I-4 isn't diagonal? It's about as close to 45° as you can get.

I'd say it's straight up east west from Tampa to Orlando, and north-south from Orlando to Daytona Beach.

[PNWRoadgeek]

I-59 also pretty darn diagonal.

Indeed it is, the long I-20 concurrency definitely helps out by being so long.

[TheStranger]

Of note: 

I brought it up earlier with I-71 and US 42, but it's notable that a lot of the diagonal interstates parallel diagonal US routes themselves:

I-59 and I-81 - US 11
I-30 - US 67 middle segment
I-4 - US 92
I-44 - old US 66 going northeast of OKC, US 62 southwest of OKC
original I-74 - US 150 and US 421

[Henry]

I-26, the western I-76, I-82, and the eastern I-88 are diagonal as well.

[SEWIGuy]

I think a poster here mentioned once that what probably would have helped is if a range of numbers was specifically set aside for diagonal routes. It also would have helped is having a consistent logic for numbers: i.e. is a route's number determined by its terminus, or its rough location within the country? US-11's numbering makes sense if you consider its northern terminus, but its southern terminus is well out of alignment. Then you have something like US-30 which makes sense for most of its length, but it's effectively flipped in Oregon, being north of US-20 instead of south. (Although this is due to US-20 originally ending near Yellowstone).

Why do we need a range of numbers for diagonal routes? The vast majority of travellers for the vast majority of trips don't take the entire route. Even if routes are simply patched together, unless the numbering is confusing for navigation, I'm not seeing why its a problem if a specific highway is out of place in the grid, OR a diagonal route switches number a dozen times as it traverses the country.

[PColumbus73]

I feel like adding more rules to the Interstate / US system eventually becomes pointless. The base even/odd rules make it flexible enough to accommodate terrain and travel patterns. If we had a rigid hexagonal numbering system, then there'd be debates on whether I-95 runs from New Brunswick to Boston, or from Cleveland to Miami.

[Rothman]

Yo momma's diagonal.