Only in these two states...

[kphoger]

Also in looking up Illinois's internal tabbed signs, some of them are centered:
https://www.google.com/maps/@41.8025706,-87.6309606,3a,75y,15.94h,88.17t/data=!3m7!1e1!3m5!1sIhUdv3pvOOxjoNkaiMpTZw!2e0!6s%2F%2Fgeo1.ggpht.com%2Fcbk%3Fpanoid%3DIhUdv3pvOOxjoNkaiMpTZw%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D52.43767%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192
https://www.google.com/maps/@41.8233501,-87.6300093,3a,75y,2.38h,108.18t/data=!3m7!1e1!3m5!1sYDzUJKLfhWbGPMULkpDLjA!2e0!6s%2F%2Fgeo1.ggpht.com%2Fcbk%3Fpanoid%3DYDzUJKLfhWbGPMULkpDLjA%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D78.743866%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192

full width  =  centered  ?

[Big John]

^^ Was the pictorial stop ahead sign adopted in 1971?

Washington and Oregon: centered exit tabs.

I'm not aware of other states that center their exit tabs. WA uses full-width internal exit tabs*, whereas Oregon uses actual tabs mounted above the sign, but both centrally-mount the legend and, in the case of Oregon, the actual tab itself.

* exception being SW WA, which does things weirdly and likes to use actual tabs mounted on the right edge of a sign as is normal elsewhere.

The 1971 Los Angeles exit numbering experiment had centered tabs as well:
https://www.aaroads.com/forum/index.php?topic=3442.0 (thread I began on that topic in 2010)


Also in looking up Illinois's internal tabbed signs, some of them are centered:
https://www.google.com/maps/@41.8025706,-87.6309606,3a,75y,15.94h,88.17t/data=!3m7!1e1!3m5!1sIhUdv3pvOOxjoNkaiMpTZw!2e0!6s%2F%2Fgeo1.ggpht.com%2Fcbk%3Fpanoid%3DIhUdv3pvOOxjoNkaiMpTZw%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D52.43767%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192
https://www.google.com/maps/@41.8233501,-87.6300093,3a,75y,2.38h,108.18t/data=!3m7!1e1!3m5!1sYDzUJKLfhWbGPMULkpDLjA!2e0!6s%2F%2Fgeo1.ggpht.com%2Fcbk%3Fpanoid%3DYDzUJKLfhWbGPMULkpDLjA%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D78.743866%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192

Was the pictorial stop ahead sign adopted in 1971?

[CoreySamson]

Here's two I have concerning Texas:

Texas and New Mexico: only states that use horizontal traffic signals consistently throughout the entire state (barring a few exceptions)
Texas and Oklahoma: only states that seem to sign clearance on every freakin bridge

[JayhawkCO]

Here's a good one, and near and dear to my heart being born in Minnesota and living in Colorado:

Minnesota & Colorado - Have two or more non-neutral colors on the state route shield.

Chris

[Terry Shea]

California and Iowa: Have letter-number county routes

Disqualified, as some exist in Illinois as well.

New Mexico as well.

Chris

That makes it a double secret disqualification!

[NWI_Irish96]

Florida and Indiana: A strict grid numbering system

New Jersey and Indiana: 1xx must be related to xx (and the same for all 3-digit routes)

Because Indiana mimics the US highway system in both of these ways, I was about 12 years old before I realized that not every state does the same thing.

[kphoger]

Because Indiana mimics the US highway system in both of these ways, I was about 12 years old before I realized that not every state does the same thing.

How long before you realized that a state doesn't have to have any pattern at all, and people still don't get lost or wonder what part of the state they're in?

I tell you, I wish all route numbers were just randomly assigned.  I hate clusters of similarly-numbered routes.

[Flint1979]

Florida and Indiana: A strict grid numbering system

New Jersey and Indiana: 1xx must be related to xx (and the same for all 3-digit routes)

Because Indiana mimics the US highway system in both of these ways, I was about 12 years old before I realized that not every state does the same thing.

I don't know why but I realized that pretty quick about Indiana. I was traveling down I-69 one day and noticed that the state highways were going in order and after looking at a map of Indiana I thought this looks exactly like the US highway system on a state highway system.

[kphoger]

I don't even remember anymore:  where is I-366 supposed to have an 85-mph speed limit?  We can add that to Texas.

[kphoger]

ARGUMENT TIME

Which two states' panhandles actually deserve to be called panhandles?

[ozarkman417]

Oklahoma, because you could argue that the state itself looks like a pan, though a disfigured one.

The other one was a bit more difficult to decide on. I eliminated NE and TX because I think they are too thick, while AK's is more so a series of islands. There remain a few, like Idaho and West Virginia, but, in my opinion, the one that looks the panhandleist of the remaining ones is Florida's.

[cl94]

New York and New Hampshire: Regularly have alternate routes that go through the alphabet, such as NY 17K and NH 11D

Not true–this is a distinct feature of the Oklahoma route numbering system as well (reaching all the way up to SH-74F on the most-suffixed route, with one-offs for mnemonic reasons for 77H, 77S, and 412P).

Vermont has a handful as well.

If we want to count internal suffixes, throw CO and MD onto the list, because they get quite high.

[Ned Weasel]

Also before I officially say that it's only in these 2 states...
Do any other states besides Indiana and Ohio posts these blue signs at exit and entrance ramps?

Kansas does this, but it might just be a Wichita thing.  Not sure about the rest of the state.
example
example
example
example

I was pretty sure I saw them somewhere that wasn't Wichita, Indiana, or Ohio: https://goo.gl/maps/6xgYeKg172krJEcK6

How about this one?  Michigan and New Jersey:  The only two states to popularize a unique style of left turn substitution.  Unless you count Texas Turnarounds or roundabouts.

[kphoger]

How about this one?  Michigan and New Jersey:  The only two states to popularize a unique style of left turn substitution.  Unless you count Texas Turnarounds or roundabouts.

OK, what state are you saying has uniquely popularized the roundabout?

[hotdogPi]

How about this one?  Michigan and New Jersey:  The only two states to popularize a unique style of left turn substitution.  Unless you count Texas Turnarounds or roundabouts.

OK, what state are you saying has uniquely popularized the roundabout?

Outside the US. They're everywhere in Europe.

[Ned Weasel]

OK, what state are you saying has uniquely popularized the roundabout?

I wasn't exactly saying that, although I would have guessed Massachusetts, but I also wouldn't have been entirely correct, as Wikipedia says the first modern roundabout in the U.S. was built in Nevada in 1990 (https://en.wikipedia.org/wiki/Roundabout#Development_of_modern_roundabouts).

[OCGuy81]

Michigan and North Carolina: only two states with diamond shaped highway markers?

[tdindy88]

Michigan and North Carolina: only two states with diamond shaped highway markers?

Aren't they also the only states that sign their central business districts "DOWNTOWN" on their highway signs? Or does another state do that as well?

[OCGuy81]

Michigan and North Carolina: only two states with diamond shaped highway markers?

Aren't they also the only states that sign their central business districts "DOWNTOWN" on their highway signs? Or does another state do that as well?

I recall seeing that along I-10 and I-45 in the Houston area

[Revive 755]

Here's two I have concerning Texas:

Texas and New Mexico: only states that use horizontal traffic signals consistently throughout the entire state (barring a few exceptions)

Nebraska at least used to mostly use horizontal signals except for the Omaha area and span wire installations.  The Lincoln area has since switched to vertical.

[Elm]

Michigan and North Carolina: only two states with diamond shaped highway markers?

Aren't they also the only states that sign their central business districts "DOWNTOWN" on their highway signs? Or does another state do that as well?

I recall seeing that along I-10 and I-45 in the Houston area

Colorado has some of those, too. On I-25, exit 142 is Bijou St/Downtown for Colorado Springs, and southbound exit 213 is 38th Ave/Park Ave/Downtown for Denver. Some express lane signs reference "Downtown"  further out, like here on US 36.

[TheStranger]

Michigan and North Carolina: only two states with diamond shaped highway markers?

Aren't they also the only states that sign their central business districts "DOWNTOWN" on their highway signs? Or does another state do that as well?

I recall seeing that along I-10 and I-45 in the Houston area

Colorado has some of those, too. On I-25, exit 142 is Bijou St/Downtown for Colorado Springs, and southbound exit 213 is 38th Ave/Park Ave/Downtown for Denver. Some express lane signs reference "Downtown"  further out, like here on US 36.

Downtown signage off of 110/Harbor Freeway northbound past I-10 in Los Angeles:
https://www.google.com/maps/@34.0402227,-118.2735916,3a,75y,39.3h,97.26t/data=!3m6!1e1!3m4!1skAda1l92hX2u-ASVNj1dug!2e0!7i16384!8i8192

[dkblake]

OK, what state are you saying has uniquely popularized the roundabout?

I wasn't exactly saying that, although I would have guessed Massachusetts, but I also wouldn't have been entirely correct, as Wikipedia says the first modern roundabout in the U.S. was built in Nevada in 1990 (https://en.wikipedia.org/wiki/Roundabout#Development_of_modern_roundabouts).

Is roundabout some strange non-Massachusetts term for rotary?

[ran4sh]

New York and South Carolina: Exit number tab on freeway signs is right-aligned not to the right edge of the sign, but at the point where the border's corner transitions from straight to curve. Although new NY signs don't do this anymore.

NY example: https://goo.gl/maps/pM8qrmS5SdQ1jMzu5

SC example: https://goo.gl/maps/QgpG5B48YsQzn6Zf8

This looks better on the NY signs because the corner is actually rounded, compared to the SC signs.

[Roadgeekteen]

Arizona and New Mexico:

No 3DIs