Highways that are isolated from the state they are located in

[Quillz]

You got it right.  Georgia mile markers, would-be Tennessee exit numbers.  

I know I'm straying waaaaay off topic, but does this situation exist anywhere else on interstate system, i.e. mile markers reflect "home" state mileage, but exit numbers correspond to neighboring state's "would-be" mileage?

NY-17 (future I-86) briefly passes into Pennsylvania but is still maintained by NYDOT. No idea if it actually has any exits on the very brief alignment, though.

Also, CA-161 (really getting off-topic here, sorry) is very close to the Oregon border, but I'm not sure if it actually touches it or not.

[mightyace]

Exit 60 for US 220 is entirely in Pennsylvania.
Exit 61 for NY 34/PA 199 has most of the eastbound ramps in PA.

http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Waverly,+NY&sll=37.0625,-95.677068&sspn=50.244827,51.591797&ie=UTF8&hq=&hnear=Waverly,+Tioga,+New+York&ll=41.999655,-76.537113&spn=0.023218,0.025191&t=h&z=15

I have no idea whose mileposts are used.

[SidS1045]

NY 120A, which runs along the NY/CT border, veers completely into CT for a bit...but is still maintained by NYSDOT.

[vdeane]

Exit 60 for US 220 is entirely in Pennsylvania.
Exit 61 for NY 34/PA 199 has most of the eastbound ramps in PA.

http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Waverly,+NY&sll=37.0625,-95.677068&sspn=50.244827,51.591797&ie=UTF8&hq=&hnear=Waverly,+Tioga,+New+York&ll=41.999655,-76.537113&spn=0.023218,0.025191&t=h&z=15

I have no idea whose mileposts are used.

I would assume NY's, given that it's maintained by NYSDOT.

[mightyace]

^^^

I would think so, too.  But, it's been over 25 years since I've been on that stretch of highway and I don't care to take the time to slug through Google streetview.

These exits may be the last exits in PA with sequential numbering.

[Duke87]

NY 120A, which runs along the NY/CT border, veers completely into CT for a bit...but is still maintained by NYSDOT.

It makes no less than four crossings of the state line (six southbound, if Google Maps is accurate), one of which involves a significant length straddling it. It intersects with CT 15 while straddling, so the southern of its two ventures into Connecticut isn't isolated. But the northern one is.

[Michael in Philly]

Re. the purported Md. 896:  I once drove 896 between Newark and some place in Pennsylvania to see if it was marked in Maryland.  It was not.  This was probably over 15 years ago, so if someone knows it's changed, please feel free to say so.
And I think I-684 in Connecticut is a special degree of isolation in that you can't get off (or on to) it in Connecticut.  Which takes it beyond roads like, um, not(?)-Md.-896 in not having any intersections with even unnumbered roads in the state.  If you know what I mean.
(The 2009-2010 Maryland official road map shows Del. and Pa. 896, but not Md. 896.  By which I mean they have oval 896 markers in Delaware and Pennsylvania but no rectangle-with-a-top-part 896 marker in Maryland.)

[Alps]

Re. the purported Md. 896:  I once drove 896 between Newark and some place in Pennsylvania to see if it was marked in Maryland.  It was not.  This was probably over 15 years ago, so if someone knows it's changed, please feel free to say so.
(The 2009-2010 Maryland official road map shows Del. and Pa. 896, but not Md. 896.  By which I mean they have oval 896 markers in Delaware and Pennsylvania but no rectangle-with-a-top-part 896 marker in Maryland.)

I want to say that they did have a Maryland reassurance when I crossed the border, but it may have just been Welcome to Maryland.  Either way, it's definitely MD 896.

I take that back.  No trace of welcome or reassurance signage according to Google.

[Crazy Volvo Guy]

I-684 in CT cannot be accessed from within CT, you have to go into NY to get on it.

[J N Winkler]

Also, CA-161 (really getting off-topic here, sorry) is very close to the Oregon border, but I'm not sure if it actually touches it or not.

I believe it straddles the actual border, but I was not able to find monumentation to prove it when I travelled its entire length in 2003.  (I don't consider pavement joints or the location of welcome signage to be reliable evidence.  At the US 50 crossing of the Kansas-Colorado border, for example, Colorado has made a naked land grab and put the Prower County line sign, done to CDOT standards for the signface design and on a typical CDOT slip base, on the Kansas side.)

[yakra]

ME 113 enters New Hampshire twice and both are maintained by NHDOT. NHDOT even signs ME 113 with Maine's square. There is even a spur off of it, NH 113B, in Chatham.

Damn you, you beat me to it!

So how about NB774? There are ferries, but no roads to the rest of New Brunswick without taking the bridge into the United States.

[jwolfer]

Not sure if there is a shorter name for this phenomenon-but these are highways that run through a portion of a state that is completely isolated from the rest of the state-i.e. you must go through an adjoining state to reach the rest of the state by road. The longest example of this would probably be I-15 in Arizona. Another would be I-684 which goes through a small portion of Connecticut. US 212 does this twice-in the northeast corner of Wyoming and again in Montana just NE of Yellowstone NP. Another one I know of is IA 165 in Carter Lake, IA-which is part of the road between downtown Omaha and Eppley Airfield. Other examples?

Not sure if there is a shorter name for this phenomenon-but these are highways that run through a portion of a state that is completely isolated from the rest of the state-i.e. you must go through an adjoining state to reach the rest of the state by road. The longest example of this would probably be I-15 in Arizona. Another would be I-684 which goes through a small portion of Connecticut. US 212 does this twice-in the northeast corner of Wyoming and again in Montana just NE of Yellowstone NP. Another one I know of is IA 165 in Carter Lake, IA-which is part of the road between downtown Omaha and Eppley Airfield. Other examples?

SR2 in Baker and Coumbia County FL you have to enter GA or use county roads to reach another state highway... not quite haveing to enter another state

[hbelkins]

The route leading into Kentucky Bend in far western Kentucky (an extension of TN 22) once upon a time carried a state route number, KY 313. It is shown on the 1973 and 1976 official state highway maps (which are available online). By 1983, it was no longer a state highway (and had been paved). It had been decommissioned by 1981, when the official orders were posted.

[Andrew T.]

West Virginia state highway 102 in Mercer County touches no other state highways, and begins and ends at the Virginia state line.

[hbelkins]

West Virginia state highway 102 in Mercer County touches no other state highways, and begins and ends at the Virginia state line.

If I'm not mistaken there is at least one "county" highway -- actually maintained by the state -- that connects WV 102 to US 52.

[Quillz]

I feel like CA-186 is eligible. About a mile long or so, only touches I-8 and it's entire purpose is to serve a little-used border crossing near Winterhaven.