Only in these two states...

[hobsini2]

California and Iowa: Have letter-number county routes

Illinois has some Letter-Number county highways especially in Lake and Cook County.
https://www.google.com/maps/@42.4297562,-88.1179384,3a,51.6y,42.2h,87.09t/data=!3m6!1e1!3m4!1sVStk888TwG5fNwow8w3VEA!2e0!7i16384!8i8192?hl=en

As for Interstate bumps,

[hobsini2]

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)

Wisconsin did the horizontal signals only up until a few years ago.

[hobsini2]

ARGUMENT TIME

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

There are 3 legit state panhandles. Oklahoma, Texas and West Virginia. HOWEVER, Texas should be disqualified because it does not look like a panhandle. Connecticut looks more like a pot handle in the SW.

[hobsini2]

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?

Had been Massachusetts but now I would say Wisconsin. Every single new interchange redesign has them.

[roadfro]

Returning to a bit more of a roadgeek focus...

CA & NV: Only two states with a county-based mileage reference system to use white postmile/milepost paddles.

I might be wrong on this but here goes.

CA and WA: only two states that use Freeway Entrance signage at every interchange.

Not sure if it's every interchange, but I found some Nevada examples

I knew Nevada used them quite a bit, but I wasn't sure if it was at every ramp. California and Washington seem to

MT has been putting these up throughout the state. Not sure if on every entrance, but I have seen them on pretty much every one I can think of.

Add West Virginia to that list.

There's a "Freeway Entrance" signage on the Traffic Control board that notes many states using such signage. However, California & Nevada appear to be the only two that post these consistently at every* freeway on-ramp with the entire "freeway entrance sign package"–the MUTCD-standard sign, route shield, cardinal direction, and downward arrow.

(* Exception is Summerlin Parkway in Las Vegas, which until recently was not state-maintained.)

[kurumi]

OH and PA: each have four consecutive 2di's (74-77 and 78-81). I'm not really worried about I-73 ruining this one

[JayhawkCO]

OH and PA: each have four consecutive 2di's (74-77 and 78-81). I'm not really worried about I-73 ruining this one

Technically, Alaska?

Chris

[wriddle082]

(There may be others that I'm not aware of, but this gets the conversation going)

Alabama and Colorado:  when they close a lane for construction, they always set the flashing arrow signs to three chevrons mode instead of just a flashing arrow.  The chevrons flash in a sequence similar to current model Ford Mustang rear turn indicators.

[US 89]

(There may be others that I'm not aware of, but this gets the conversation going)

Alabama and Colorado:  when they close a lane for construction, they always set the flashing arrow signs to three chevrons mode instead of just a flashing arrow.  The chevrons flash in a sequence similar to current model Ford Mustang rear turn indicators.

This is extremely common in Utah and probably a lot of other states. I'm pretty sure I've seen it in Georgia, too.

[X99]

(There may be others that I'm not aware of, but this gets the conversation going)

Alabama and Colorado:  when they close a lane for construction, they always set the flashing arrow signs to three chevrons mode instead of just a flashing arrow.  The chevrons flash in a sequence similar to current model Ford Mustang rear turn indicators.

This is extremely common in Utah and probably a lot of other states. I'm pretty sure I've seen it in Georgia, too.

South Dakota does three chevrons as well. I don't think I've ever seen a regular arrow on one of those signs here.

[Scott5114]

Meanwhile, the arrow boards commonly used in Oklahoma don't even have the capability to display chevrons. The lights are arranged in just the pattern of a double-headed arrow.

Kansas arrow boards can display chevrons but I've never seen them do so. I think I've seen them display an animated arrow that "grows" across the face of the sign.

I've always wondered if there was any intended semantic difference between the chevrons and the arrow. The Oklahoma driver's manual shows both and, by using different wording under each of them, implies there is, but doesn't make it entirely clear what the difference is (I think one is "lane closed" and one is "move left/move right" or something like that).

[OCGuy81]

ND and VT: only states in the lower 48 that don't have an x0 or x5.

[RobbieL2415]

CT and WV: only two states to share the bold-border square SR shield design. MA, RI and ME are square but their borders are thinner.

[ethanhopkin14]

CT and WV: only two states to share the bold-border square SR shield design. MA, RI and ME are square but their borders are thinner.

Texas would like to have a word.

[Scott5114]

CT and WV: only two states to share the bold-border square SR shield design. MA, RI and ME are square but their borders are thinner.

Texas would like to have a word.

The word it would like to have is "TEXAS", which isn't included in CT and WV's shields. (Note that IL, IN, and MT weren't listed alongside MA, RI, and ME.)

[Big John]

^^ Rhode Island has R.I. on the state highway shield.

[Gnutella]

Pennsylvania and Delaware are the only states with a round land border.

[dvferyance]

GA and TN only states with 3 x5 interstates.
GA 75,85,95
TN 55,65,75

[US 89]

Do any states besides Nevada and Colorado use these black-and-blue paddles to mark emergency vehicle median crossings on interstates? Both states use a pattern where there'll be one paddle upstream of the crossing as an warning that it's coming, and then one on either side of the crossing.

I could be wrong but I don't think I've ever seen them anywhere else.

[kphoger]

Do any states besides Nevada and Colorado use these black-and-blue paddles to mark emergency vehicle median crossings on interstates? Both states use a pattern where there'll be one paddle upstream of the crossing as an warning that it's coming, and then one on either side of the crossing.

I could be wrong but I don't think I've ever seen them anywhere else.

I've seen blue reflectors used in some places where white or yellow might otherwise be used, although I can't remember where at the moment.  But not the paddles.

[CtrlAltDel]

I was bored, so here you go:

Alabama and Alaska are the only two states to start with the letters A L A and to also end in A.

California (CA) and Colorado (CO) are the only two states with names that start with C and postal abbreviations with a second letter that could be either the second or last letter of the state's name.

Louisiana/Alabama (LA/AL) and Minnesota/New Mexico (MN/NM) are the only two pairs of states with postal abbreviations composed of the same letters.

Connecticut and Mississippi are the only states with names that are eleven letters long.

North Dakota and South Dakota are the only two states admitted on the same day.

Tennessee and Missouri are the only two states to border eight other states.

Colorado and Kentucky are the only two states to border seven other states.

Also, there are six states with postal abbreviations one letter apart, three increasing (Delaware (DE), Hawaii (HI), and Minnesota(MN)) and three decreasing (New Mexico (NM), Utah (UT), and West Virginia (WV)).

The biggest increasing gap between the letters of the postal abbreviations is found, of course, with Arizona (AZ), while the biggest decreasing gap is Washington (WA).

[Scott5114]

California (CA) and Colorado (CO) are the only two states with postal abbreviations with a second letter that could be either the second or last letter of the state's name.

DElawarE

[OCGuy81]

Oregon and Maine.

Only two states with Portland being the largest city.

[CtrlAltDel]

California (CA) and Colorado (CO) are the only two states with postal abbreviations with a second letter that could be either the second or last letter of the state's name.

DElawarE

Dammit.

[ran4sh]

California (CA) and Colorado (CO) are the only two states with postal abbreviations with a second letter that could be either the second or last letter of the state's name.

DElawarE

Dammit.

Well, some say that they "could be" either the second or last letter, but the 2 letter abbreviations generally were derived from the traditional abbreviations which are used by, e.g. the Associated Press. CA comes from Calif., CO comes from Colo., DE comes from Del. - so in all three of those states it's the 2nd letter and not the last that is used for the abbreviation.