Only in these two states...

[hotdogPi]

Florida and Indiana: A strict grid numbering system
Georgia and Ontario (yes, I know that's not a state): 400-series freeways
Michigan and Kansas: State route abbreviations are M- and K- instead of MI and KS
Illinois and New York: Have an intrastate I-88
Minnesota and Texas: Have suffixed Interstate routes
Missouri and Wisconsin: Have lettered routes
California and Iowa: Have letter-number county routes
Alaska and South Dakota: Capital has no freeway
Illinois and Ohio: Have an Interstate "bump" (as far as I'm aware)
Arkansas and Indiana: Allow duplicating state route numbers with no restrictions
Alaska and Hawaii: Have no US routes
Texas and Kentucky: Have enough routes that their statewide route system has to go to 4 digits
New Jersey and Indiana: 1xx must be related to xx (and the same for all 3-digit routes)
Massachusetts and Maine: Use a thin-bordered blank square as a shield
Connecticut and West Virginia: Use a thick-bordered blank square as a shield
Idaho and Louisiana: State route shield colors can be either normal or inverted with no difference
California and Vermont: Green state route shields (if we're considering states only)
Wyoming and Illinois: Have a pointless I-180
New York and New Hampshire: Regularly have alternate routes that go through the alphabet, such as NY 17K and NH 11D

(This thread is also open to traffic signals, traffic laws, DOTs, etc., as well as historical road-related comparisons.)

[ilpt4u]

Illinois has 2 of those Interstate Bumps...

Are 76/80, 74/80, and 64/70 really the only 3 that exist?

[roadman65]

Then PA and La both use  local destinations as control cities for interstates.

[Mapmikey]

Georgia and Ontario (yes, I know that's not a state): 400-series freeways

Tennessee at least had 400-series designations on its interstates but I have to contact TDOT to see if that is still true

[froggie]

California and Iowa: Have letter-number county routes

Disqualified, as some exist in Illinois as well.

[webny99]

Is I-271/I-480 the only multiplex of 3dis? If there's one I'm forgetting then that state could be paired with Ohio.

[JayhawkCO]

Louisiana has plenty of 4 digit state routes.

Chris

[jmacswimmer]

Is I-271/I-480 the only multiplex of 3dis? If there's one I'm forgetting then that state could be paired with Ohio.

I-785/I-840 in NC (although I-840 is currently unsigned along the concurrency until its entire length is complete).

[JayhawkCO]

Colorado & Hawai'i: The only two states with paved roads above 11,000'

Chris

[hotdogPi]

Louisiana has plenty of 4 digit state routes.

Chris

Did they run out of 3-digit numbers, though?

[JayhawkCO]

California and Iowa: Have letter-number county routes

Disqualified, as some exist in Illinois as well.

New Mexico as well.

Chris

[WillWeaverRVA]

Georgia and Ontario (yes, I know that's not a state): 400-series freeways

Tennessee at least had 400-series designations on its interstates but I have to contact TDOT to see if that is still true

Weren't there also 4xx designations for various interstates in Virginia at one point? I know I-495 was internally designated VA 413 through at least the early 2000s.

[Mapmikey]

Georgia and Ontario (yes, I know that's not a state): 400-series freeways

Tennessee at least had 400-series designations on its interstates but I have to contact TDOT to see if that is still true

Weren't there also 4xx designations for various interstates in Virginia at one point? I know I-495 was internally designated VA 413 through at least the early 2000s.

Yes.  These internal designations went away in the late 1950s/early 60s and project numbers after that used the interstate numbers once coincident state route designations were changed.  The appearance of 413 on more recent documents is a legacy error - a fully posted VA 413 has been around since since 1981.

[kphoger]

California and Iowa: Have letter-number county routes

Disqualified, as some exist in Illinois as well.

New Mexico as well.

↓  New Mexico  ↓  01-OCT-2020  ↓

[kphoger]

Arkansas and Indiana: Allow duplicating state route numbers with no restrictions

Do you mean they have multiple state routes with the same number, or do you mean their state route numbers duplicate US- or I- route numbers?

[hotdogPi]

Arkansas and Indiana: Allow duplicating state route numbers with no restrictions

Do you mean they have multiple state routes with the same number, or do you mean their state route numbers duplicate US- or I- route numbers?

Multiple state routes with the same number.

[JayhawkCO]

Louisiana has plenty of 4 digit state routes.

Chris

Did they run out of 3-digit numbers, though?

They don't use 200-300, but there are far more than 100 4-digit routes.  Including business, unconnected, and hyphenated routes, there are 1234 state highways in Louisiana.  If you eliminate those multiples (quick count), there are 1124.  So four digits would indeed be required.

Arkansas and Indiana: Allow duplicating state route numbers with no restrictions

Do you mean they have multiple state routes with the same number, or do you mean their state route numbers duplicate US- or I- route numbers?

Multiple state routes with the same number.

So on that note, I think you can add Louisiana to this list too, eliminating that one.

Chris

[TheHighwayMan3561]

Dodge County, MN has some lettered county highways; I imagine other isolated places probably do as well.

[kphoger]

I will say this about the alphanumeric county route thing, though...  California and Iowa have a statewide (except Lake County, CA) system for numbering (or at least lettering) them.  New Mexico and other isolated areas don't have that.

[SkyPesos]

Illinois and Ohio: Have an Interstate "bump" (as far as I'm aware)

Kind of wondering, which other states have freeway bumps (doesn't have to be interstate). Off the top of my head, although not a state, there's one between ON 403 and ON 407

Also is there a state that uses APL signage as extensively as BC? That would be another pair.

[NWI_Irish96]

Illinois and Ohio: Have an Interstate "bump" (as far as I'm aware)

Kind of wondering, which other states have freeway bumps (doesn't have to be interstate). Off the top of my head, although not a state, there's one between ON 403 and ON 407

Also is there a state that uses APL signage as extensively as BC? That would be another pair.

IN 2 and US 20 aren't freeways, but they do bump at an interchange.

[KCRoadFan]

California and Iowa: Have letter-number county routes

Disqualified, as some exist in Illinois as well.

New Mexico as well.

Chris

Michigan as well

[KCRoadFan]

New Jersey and Oregon: no self-service gas.

[TheHighwayMan3561]

New Jersey and Oregon: no self-service gas.

Oregon relaxed that law somewhat, but functionally you can only self serve if no one lives there.

[Life in Paradise]

Arkansas and Indiana: Allow duplicating state route numbers with no restrictions

Do you mean they have multiple state routes with the same number, or do you mean their state route numbers duplicate US- or I- route numbers?

Multiple state routes with the same number.

In Indiana it is more that IDOT has dropped roads in cities off their rolls, making roads non-congruent on each side of the city, or have neglected to either co-sign a connecting road or have dropped a highway (such as the upcoming IN-37 exit of the I-69 corridor south of Indy) leaving remaining segments on each side.