Only in this state....

[KEK Inc.]

California has a pretty large list.

[SSOWorld]

Only in Wisconsin - one piece sine salads and ladder-like signal mast arms.

[NE2]

Only in Wisconsin - one piece sine salads

This and others on http://www.alpsroads.net/roads/ri/us_6/

[jeffandnicole]

Only in Delaware: Blinking green signals.

Where exactly in Delaware have you seen flashing green signals? I've heard of them existing in Massachusetts, but I didn't know anywhere else in the US had them.

I remember seeing one on DE 1 between Dover and Rehoboth.

There was one on DE 7 near Hockessin as well in the 90's...it's now a regular traffic light.  In fact, I think there was 3 in New Castle County; none of which remain.

Most people think jughandles are only in NJ, but they definitely exist elsewhere. Here's one that's pretty uniquely NJ: traffic circles with ambiguous traffic control and at least one leg, if not two or more legs, where the entrance has priority over the circle.

Along with numerous entrances/exits of private businesses directly into and out of the circle via curb cuts.  And in at least one case, a gas station directly in the middle of the circle.

[DaBigE]

Only in Wisconsin - one piece sine salads and ladder-like signal mast arms.

IIRC, I've seen the "ladder-like" (a.k.a. trombone arms) in areas Pennsylvania and Texas. Illinois has a variation on it as well (curved arm).

[StogieGuy7]

Only in Connecticut:  BGS's with reflective button copy and route markers on the signs with green backgrounds.

California was the originator of this concept and you can still see plenty of examples there.  CT - for some reason - resurrected this (at the time) 25 year old concept in the 1980s but discontinued it about 20 years ago.

Only in Vermont: Yellow signs that warn of frost heaves.

No, not only in Vermont.  New Hampshire, Maine and Massachusetts commonly have such signs.

Only in New York: The little green reference markers every 1/5 of a mile

The format may be unique to New York, but the concept is common.  One could say the same of the complex little black on white markers that highways in CA have had for decades. 

Only in Delaware: Blinking green signals.

This is common in many other countries, it usually implies that the green period is about to end - but can also mean "left turn only".   Depends where you are. 

[Henry]

Only in IL: States as control cities (especially around Chicagoland)

[vdeane]

VT has green reference markers as well, but at irregular intervals.

Only in NY: boxed street names on guide signs
Only in ON: using a different font size for every control city on a sign
Only in QC: those yellow trapezoids that replace the exit tab

[Big John]

Only in Wisconsin - one piece sine salads and ladder-like signal mast arms.

IIRC, I've seen the "ladder-like" (a.k.a. trombone arms) in areas Pennsylvania and Texas. Illinois has a variation on it as well (curved arm).

And trombone arms are common in New Jersey and New Mexico.

[Scott5114]

Only in IL: States as control cities (especially around Chicagoland)

There are some instances of MoDOT doing this as well ("Kansas" for I-635, "Illinois" for I-55 NB).

[BamaZeus]

Not sure if it's elsewhere, but when I think of Massachusetts, I immediately think of text signs with arrows through the numbers

http://www.flickr.com/photos/33445721@N04/6454615515/

[jeffandnicole]

Only in Delaware: Blinking green signals.

This is common in many other countries, it usually implies that the green period is about to end - but can also mean "left turn only".   Depends where you are. 

While the flashing green is common in other countries, the use of it in Delaware was vastly different.

In Delaware, the main road would have a flashing green; the side road would have a flashing red.  The concept was that traffic on the side road would be permitted to enter the intersection when safe to do so.  But unlike a flashing yellow/red combo, if traffic remained on the side road too long, the traffic light would quit flashing and would go into normal mode.  After the side road received the green light (then yellow, then red), the main road would get the steady green again.  After a few moments, the light would change back to flashing green/flashing red.

While the thinking behind it was sound - no need to stop the traffic on the main road when a single car on a side road could find a break in traffic - it was a bit confusing because it was too unique, especially to those that never encountered such a signal.  And traffic volumes were rising on these roads, decreasing the significant breaks in traffic that allowed this type of signal to work properly.  Thus, the flashing green/red was eliminated from the Delaware landscape.

[Alex]

Only in Delaware: Blinking green signals.

Where exactly in Delaware have you seen flashing green signals? I've heard of them existing in Massachusetts, but I didn't know anywhere else in the US had them.

I remember seeing one on DE 1 between Dover and Rehoboth.

There was one on DE 7 near Hockessin as well in the 90's...it's now a regular traffic light.  In fact, I think there was 3 in New Castle County; none of which remain.

One was located on Chapman Road at Regal Boulevard. I regularly saw this one as I attended adjacent Christiana High School. Another, as you mentioned, was indeed on DE 7 toward Hockessin. The one on DE 7 was in use before Limestone Road was fully four-laned. It may have been at Valley Road or Brackenville Road, but I cannot remember.

[roadman65]

Only in Virginia is the mileage signs on off freeways posted along with the reassurence shields post intersection.

Only in New Jersey is the jughandle system used statewide.  Although parts of other states use it, but not as regular as New Jersey.

Also in New Jersey exclusively are mast arms used more than the amount of directions in places.  Sometimes you can find up to eight individual mast arms at one intersection with only four ways of movement/ direction.
In the Garden State you will find one signal head placed to the left of the center line unless there is a left turn signal.  In addition the Emergency Signals are usually out completely instead of the typical flashing yellow.  In many areas here, the light goes on during an emergency and then turns back off once the response vehicle leaves the intersection.
http://maps.google.com/maps?q=Colonia,+Woodbridge+Township,+NJ&hl=en&ll=40.600016,-74.313583&spn=0.004122,0.009345&sll=27.698638,-83.804601&sspn=9.834914,19.138184&oq=colonia,+n&t=h&hnear=Colonia,+Woodbridge+Township,+Middlesex,+New+Jersey&z=17&layer=c&cbll=40.600005,-74.313716&panoid=dAcqh6BZzTnkGpy3a4ewNQ&cbp=12,95.14,,0,0

[roadman]

Only in IL: States as control cities (especially around Chicagoland)

Until the early 1990s, it was common for BGS (and some LGS) panels on some routes in Massachusetts to use "NH-Maine" as the northbound control destination.  AFAIK, the only such signs remaining are on ramps exiting the Mass. Pike for I-95 (128) north in Weston and I-495 north in Marlborough.

Once could also argue that the "New York" destination that appears almost everywhere on I-95 south in Rhode Island refers to the state, as it doesn't include the word "City".

[The High Plains Traveler]

Only in Wisconsin - one piece sine salads and ladder-like signal mast arms.

IIRC, I've seen the "ladder-like" (a.k.a. trombone arms) in areas Pennsylvania and Texas. Illinois has a variation on it as well (curved arm).

And trombone arms are common in New Jersey and New Mexico.

The ones in New Mexico are pretty much confined to Albuquerque. Otherwise the mast arms are monotube.

[Doctor Whom]

Only in South Carolina, AFAIK:  Secondary road markers that give the county number as well as the route number (e.g., S-30-301, which is in Laurens County (#30)).

[bassoon1986]

Only in IL: States as control cities (especially around Chicagoland)

There are some instances of MoDOT doing this as well ("Kansas" for I-635, "Illinois" for I-55 NB).

and now Alabama at I-65's southern terminus.  Florida and Mississippi instead of Pensacola and Pascagoula

[bassoon1986]

Only in Louisiana (maybe not totally): Are 3di's squished into 2di shields. I know other states do this, but we seem to have it across the board. I-220 and US 171 come to mind

[thenetwork]

Only in Colorado...State Route markers that:

1) Use Five different colors in the same state route shield (the most of any numbered route shield in the US)

2) Incorporate their state flag in their state route shields.

Only in IL: States as control cities (especially around Chicagoland)

There are some instances of MoDOT doing this as well ("Kansas" for I-635, "Illinois" for I-55 NB).

and now Alabama at I-65's southern terminus.  Florida and Mississippi instead of Pensacola and Pascagoula

I-70 West in Colorado, beginning in Grand Junction, uses Utah as the Control city.

[EchoCharlieHotel]

Only in California: Arrows that point down and to the left (right) to the start of the entrance ramp on FREEWAY ENTRANCE sign assemblies. At least, CA's the only place I've seen those. Any other places have them?

Google Maps Example

[Mapmikey]

Only in South Carolina, AFAIK:  Secondary road markers that give the county number as well as the route number (e.g., S-30-301, which is in Laurens County (#30)).

Nebraska does this with their link/spur routes but I don't know if they're considered primary or secondary.

North Carolina used to do this with their 1001-series signs but I believe they've stopped doing that.

I would also argue that SC incorporates their state flag into their state highway signs.

Virginia might be the only state that doesn't allow duplication of state route numbers and secondary numbers where it would be possible to do so (e.g. North Carolina and Pennsylvania don't have 4-digit state routes; Missouri secondary routes aren't integers, etc).

Mapmikey

[theline]

Only in IL: States as control cities (especially around Chicagoland)

On most of the Indiana Toll Road the control "cities" are Chicago and Ohio.

[CentralCAroadgeek]

Only in California:
- Plentiful amounts of button-copy signage
- Internal exit tabs (though Penna has some as well)
- The FasTrak electronic tolling
- Lane markings such as the one explained on this post by myosh_tino on the "California Questions" thread:

Native California-roadgeek here.

The type of shoulder striping realjd is referring to, where the right shoulder line ends and a new one forms to the right and arcs out to form a new right shoulder line, is to indicate an upcoming freeway exit when there is poor visibility like dense fog.  According to the California MUTCD, this angled line is supposed to begin 350 feet prior to the exit.  I know this is standard in California but I am not sure if this is a national standard (my guess is probably not).

Here is an illustration of the standard California freeway shoulder striping I clipped from the California MUTCD...

All I could think of right now...

[akotchi]

I have seen isolated examples of some of the things mentioned above in other states.

New Jersey used Pennsylvania as the control city for I-95 south from U.S. 1 to the Scudders Falls Bridge, though some now say Philadelphia.

If memory serves, I have seen Freeway Entrance signs in Arizona, but I don't think the route assembly is underneath it.

I see locations in many states where 3di route numbers are in 2di shields.  Same with the U.S. route markers.

I recall in Niagara Falls seeing flashing green to mean a lead left turn phase at a signalized intersection.  This was back in 2000 when I saw it.

New Jersey, however, is the only state (DOT, anyway) whose practice is to use shields with black backgrounds (expect interstates) on their guide signs.

Pennsylvania is the only state I have seen to use a weaving area sign.  It is a warning sign (diamond), used largely in advance of auxiliary lanes with cloverleafs, with a symbol of two crossing arrows for a weaving movement.  I will see if I can get a picture, unless other Pa. participants here already have one.