What do you suspect would be the LAST number used for a new interstate?

[Quillz]

The only number between 1 and 99 not used for an interstate or US route (I mean, like ever) is 47. So that one.

I'm not a scholar when it comes to US routes, but is there any particular reason why US 47 doesn't exist?

39, 47 and 88 have never been assigned. I've never found any official reasoning, I guess it was just decided that there were enough 2- and 3-digit routes to cover the gaps. Much like interstates, it seems some US route numbers went unused in the original 1926 plan to leave space for expansion. And it's just been the case that those three numbers never found a use.

But given the US route system is still active (however slowly), perhaps one day those numbers will get used.

[national highway 1]

The only number between 1 and 99 not used for an interstate or US route (I mean, like ever) is 47. So that one.

I'm not a scholar when it comes to US routes, but is there any particular reason why US 47 doesn't exist?

39, 47 and 88 have never been assigned.

Also include 86.

[Henry]

If you count 2di's only, these numbers are still available:

1, 3, 6, 7, 9, 13, 14, 18, 21, 23, 28, 31, 32, 33, 34, 36, 38, 42, 46, 47, 48, 50, 51, 52, 53, 54, 56, 58, 60, 61, 62, 63, 67

[hotdogPi]

If you count 2di's only, these numbers are still available:

1, 3, 6, 7, 9, 13, 14, 18, 21, 23, 28, 31, 32, 33, 34, 36, 38, 42, 46, 47, 48, 50, 51, 52, 53, 54, 56, 58, 60, 61, 62, 63, 67

, 92, 98

[rbt48]

I would also guess I-1 from LA to San Francisco, though the terrain would probably preclude upgrade to interstate standards. 

Failing that, an I-42 from Tucumcari to Wichita.

[Henry]

Excluding those that don't have any 3di's, these numbers include:

905, 810, 415, 615, 715, 815, 915, 116, 216, 316, 416, 616, 716, 816, 916, 120, 32, 420, 620, 720, 920, 122, 222, 322, 522, 622, 722, 822, 922, 224, 324, 424, 524, 624, 724, 824, 924, 125, 325, 425, 525, 625, 725, 825, 925, 226, 426, 626, 726, 826, 926, 329, 429, 529, 629, 729, 829, 929, 230, 330, 830, 930, 735, 835, 935, 340, 740, 940, 145, 245, 445, 545, 645, 745, 845, 945, 455, 655, 755, 855, 955, 159, 259, 559, 659, 859, 959, 764, 864, 964, 365, 465, 665, 765, 965, 569, 669, 769, 869, 969, 570, 770, 870, 970, 171, 371, 571, 671, 771, 871, 971, 272, 372, 472, 572, 672, 772, 872, 972, 374, 574, 674, 774, 874, 974, 775, 875, 975, 776, 876, 976, 177, 377, 477, 577, 677, 777, 877, 977, 578, 778, 978, 379, 479, 679, 779, 879, 979, 681, 881, 981, 282, 382, 482, 582, 682, 782, 882, 982, 183, 383, 483, 583, 683, 783, 883, 983, 584, 684, 784, 884, 984, 387, 487, 687, 887, 987, 289, 389, 489, 589, 689, 789, 889, 989, 191, 591, 791, 891, 991, 193, 493, 593, 693, 793, 893, 993, 594, 994, 995, 396, 596, 796, 896, 996

And I apologize for the ommissions of 92 and 98 from the 2di list.

[CNGL-Leudimin]

Excluding those that don't have any 3di's, these numbers include: 684

Is this an illusion, then?

[Henry]

Excluding those that don't have any 3di's, these numbers include:

905, 810, 415, 615, 715, 815, 915, 116, 216, 316, 416, 616, 716, 816, 916, 120, 32, 420, 620, 720, 920, 122, 222, 322, 522, 622, 722, 822, 922, 224, 324, 424, 524, 624, 724, 824, 924, 125, 325, 425, 525, 625, 725, 825, 925, 226, 426, 626, 726, 826, 926, 329, 429, 529, 629, 729, 829, 929, 230, 330, 830, 930, 735, 835, 935, 340, 740, 940, 145, 245, 445, 545, 645, 745, 845, 945, 455, 655, 755, 855, 955, 159, 259, 559, 659, 859, 959, 764, 864, 964, 365, 465, 665, 765, 965, 569, 669, 769, 869, 969, 570, 770, 870, 970, 171, 371, 571, 671, 771, 871, 971, 272, 372, 472, 572, 672, 772, 872, 972, 374, 574, 674, 774, 874, 974, 775, 875, 975, 776, 876, 976, 177, 377, 477, 577, 677, 777, 877, 977, 578, 778, 978, 379, 479, 679, 779, 879, 979, 681, 881, 981, 282, 382, 482, 582, 682, 782, 882, 982, 183, 383, 483, 583, 683, 783, 883, 983, 584, 784, 884, 984, 387, 487, 687, 887, 987, 289, 389, 489, 589, 689, 789, 889, 989, 191, 591, 791, 891, 991, 193, 493, 593, 693, 793, 893, 993, 594, 994, 995, 396, 596, 796, 896, 996

And I apologize for the ommissions of 92 and 98 from the 2di list.

FTFM

[Highway63]

I would rule out any of the even numbers between 28 and 48, simply because that is NC's location on the grid...

I would not rule out any of the even numbers between 28 and 48 exactly because that is NC's location on the grid, and NC has shown it doesn't care about number rules at all.

[achilles765]

Excluding those that don't have any 3di's, these numbers include:

905, 810, 415, 615, 715, 815, 915, 116, 216, 316, 416, 616, 716, 816, 916, 120, 32, 420, 620, 720, 920, 122, 222, 322, 522, 622, 722, 822, 922, 224, 324, 424, 524, 624, 724, 824, 924, 125, 325, 425, 525, 625, 725, 825, 925, 226, 426, 626, 726, 826, 926, 329, 429, 529, 629, 729, 829, 929, 230, 330, 830, 930, 735, 835, 935, 340, 740, 940, 145, 245, 445, 545, 645, 745, 845, 945, 455, 655, 755, 855, 955, 159, 259, 559, 659, 859, 959, 764, 864, 964, 365, 465, 665, 765, 965, 569, 669, 769, 869, 969, 570, 770, 870, 970, 171, 371, 571, 671, 771, 871, 971, 272, 372, 472, 572, 672, 772, 872, 972, 374, 574, 674, 774, 874, 974, 775, 875, 975, 776, 876, 976, 177, 377, 477, 577, 677, 777, 877, 977, 578, 778, 978, 379, 479, 679, 779, 879, 979, 681, 881, 981, 282, 382, 482, 582, 682, 782, 882, 982, 183, 383, 483, 583, 683, 783, 883, 983, 584, 684, 784, 884, 984, 387, 487, 687, 887, 987, 289, 389, 489, 589, 689, 789, 889, 989, 191, 591, 791, 891, 991, 193, 493, 593, 693, 793, 893, 993, 594, 994, 995, 396, 596, 796, 896, 996

And I apologize for the ommissions of 92 and 98 from the 2di list.

I know this is old and I apologize for bumping but you left out
102, 202, 302, 402, 502, 602, 702, 802, 902, all the x27s and x 37s. Haha

[hotdogPi]

Excluding those that don't have any 3di's, these numbers include:

905, 810, 415, 615, 715, 815, 915, 116, 216, 316, 416, 616, 716, 816, 916, 120, 32, 420, 620, 720, 920, 122, 222, 322, 522, 622, 722, 822, 922, 224, 324, 424, 524, 624, 724, 824, 924, 125, 325, 425, 525, 625, 725, 825, 925, 226, 426, 626, 726, 826, 926, 329, 429, 529, 629, 729, 829, 929, 230, 330, 830, 930, 735, 835, 935, 340, 740, 940, 145, 245, 445, 545, 645, 745, 845, 945, 455, 655, 755, 855, 955, 159, 259, 559, 659, 859, 959, 764, 864, 964, 365, 465, 665, 765, 965, 569, 669, 769, 869, 969, 570, 770, 870, 970, 171, 371, 571, 671, 771, 871, 971, 272, 372, 472, 572, 672, 772, 872, 972, 374, 574, 674, 774, 874, 974, 775, 875, 975, 776, 876, 976, 177, 377, 477, 577, 677, 777, 877, 977, 578, 778, 978, 379, 479, 679, 779, 879, 979, 681, 881, 981, 282, 382, 482, 582, 682, 782, 882, 982, 183, 383, 483, 583, 683, 783, 883, 983, 584, 684, 784, 884, 984, 387, 487, 687, 887, 987, 289, 389, 489, 589, 689, 789, 889, 989, 191, 591, 791, 891, 991, 193, 493, 593, 693, 793, 893, 993, 594, 994, 995, 396, 596, 796, 896, 996

And I apologize for the ommissions of 92 and 98 from the 2di list.

I know this is old and I apologize for bumping but you left out
102, 202, 302, 402, 502, 602, 702, 802, 902, all the x27s and x 37s. Haha

You can't even bump correctly.

[SkyPesos]

1) Pick an unused 2di. I highly doubt I-1 would get used because of CA 1 and that I-3 can be used on US 101.
2) Add a 9 in front of that 2di number to make a 9xx 3di, so in this case, I-901.

There you go, an interstate number that will never be used.

[Terry Shea]

Interstate 1

I mean, where would you put it?

Right next to I-99.

[OCGuy81]

I-98 comes to mind, as there's room on the grid, but no real reason to have it.  You could route it largely along the western US-2, but there's really not any population centers to warrant it.

[kphoger]

I-98 comes to mind, as there's room on the grid, but no real reason to have it.  You could route it largely along the western US-2, but there's really not any population centers to warrant it.

Then an even better answer would probably be something like I-898.

[SkyPesos]

I-98 comes to mind, as there's room on the grid, but no real reason to have it.  You could route it largely along the western US-2, but there's really not any population centers to warrant it.

WI 29 is a possibility for I-98. Probably won't be an interstate in our lifetimes, but there are other numbers that are less likely.

[jmacswimmer]

I-98 comes to mind, as there's room on the grid, but no real reason to have it.  You could route it largely along the western US-2, but there's really not any population centers to warrant it.

WI 29 is a possibility for I-98. Probably won't be an interstate in our lifetimes, but there are other numbers that are less likely.

I think I-98 has also been linked to the "Rooftop Highway" (US 11 corridor between I-81 & I-87 in far Upstate NY) at one point or another, though I don't know whether this proposal has any serious traction behind it.

[kphoger]

What is the closest-together pair of spread-numbered Interstates with the least amount of development in between, that would still have room in the numbering for one more?

For example, there's not much between 25 and 27, but there's no odd number to use.

I see there are no even numbers between 30 and 40.  However, if there's ever a Fort Worth—Amarillo Interstate, then maybe it might get such a number.

What are the chances of an odd 2di between 49 and 55?

Et cetera.

[JoePCool14]

I-98 comes to mind, as there's room on the grid, but no real reason to have it.  You could route it largely along the western US-2, but there's really not any population centers to warrant it.

WI 29 is a possibility for I-98. Probably won't be an interstate in our lifetimes, but there are other numbers that are less likely.

I think I-98 has also been linked to the "Rooftop Highway" (US 11 corridor between I-81 & I-87 in far Upstate NY) at one point or another, though I don't know whether this proposal has any serious traction behind it.

Super fictional idea, but it would be interesting to see I-96 come over from Michigan on some ferry and have it continue on west instead of making a new Interstate.

[OCGuy81]

What is the closest-together pair of spread-numbered Interstates with the least amount of development in between, that would still have room in the numbering for one more?

For example, there's not much between 25 and 27, but there's no odd number to use.

I see there are no even numbers between 30 and 40.  However, if there's ever a Fort Worth—Amarillo Interstate, then maybe it might get such a number.

What are the chances of an odd 2di between 49 and 55?

Et cetera.

Maybe there's hope that someday I-238 meets its parent route. :-)

[hotdogPi]

Based on this thread that I created, I said that I-13 is going to require future growth on the west side of Salt Lake City, while everything else has a current corridor that could be used, and look at reply #10 in that thread.

[vdeane]

Interstate 1

I mean, where would you put it?

Right next to I-99.

US 219 corridor?

[jmacswimmer]

Interstate 1

I mean, where would you put it?

Right next to I-99.

US 219 corridor?

Perfect - then I-70/76 can go from intersecting I-1 to intersecting I-99 at the very next exit! 

[SkyPesos]

Based on this thread that I created, I said that I-13 is going to require future growth on the west side of Salt Lake City, while everything else has a current corridor that could be used, and look at reply #10 in that thread.

Definitely not needed now, but how about Winnemucca to Boise for I-13?

[Roadgeekteen]

For 3dis, I-997 probably.