Numbered routes that follow state or county lines

[KCRoadFan]

In Kansas, part of US 40 between Topeka and Lawrence goes along the Shawnee/Douglas County line.

[zachary_amaryllis]

Local example: The Weld/Larimer County line has a road along most of it.

What I always wondered, is who maintains it, and who decides what it's called. The road I speak of is generally referred to as Weld CR 13, but it's in the spot where Larimer CR 1 would go, and I've seen it occasionally referred to as Larimer CR 1 (or just County Line Road).

It doesn't look like two different counties are maintaining the road, it 'feels and drives' like a Weld County road. Is the actual county line the centerline of the road, or ... ?

[roadman65]

US 5 in VT closely follows the Connecticut River that forms the boundary with NH.

[tigerwings]

US 23 in Ohio on the Wood/Sandusky county line

[dgolub]

* King Street (NY 120A) along the border between New York and Connecticut.  In fact, despite being a New York state route, it crosses into Connecticut for a short distance at one point!
* County Line Road (Suffolk CR 1) along the border between Nassau and Suffolk counties in New York.
* Jericho Turnpike (NY 25) along the border between New York City and Nassau county for half a mile or so.

[dantheman]

It's only a town line, but an interesting example is the CT 20 freeway following the town line between Windsor and Windsor Locks, CT. The history on this one is backwards from most: the freeway was originally built kinda-sorta near the town line, but crossed it a number of times. This led to some "islands" of each town that were stranded on the wrong side of the freeway. Windsor and Windsor Locks later agreed to re-align their town line to the median of CT 20 (and a short stretch of I-91) so that both towns' land was all on the "correct" side of the freeway.

The best view of this I can find is to compare the 1966 and 1973 topo maps in this area on historicaerials.com.

[Bitmapped]

A short section of WV/VA 127 runs along the border of those two states.

Roads along the WV/VA state line are pretty common since the line is mostly a ridge. In some cases, the road may not be entirely on the state line but will bounce back and forth across it depending on terrain obstacles. WVDOH and VDOT have worked out agreements for who handles these roads, sometimes leading to one agency maintaining parts of road in the other state.

Some examples, in addition to WV/VA 127 and WV/VA 83 that were previously mentioned:
- West Virginia maintains a portion of WV/VA 259 that straddles the state line between Hardy and Frederick Counties
- A 3-mile section of Virginia SR 691 (former VA 59) bounces back and forth across the WV/VA line.
- FR 85, maintained by George Washington National Forest, closely parallels the WV/VA line. Parts of it near Reddish Knob are directly on top of the ridge, on the state line. In one part, the road is 1-lane wide with guard rails on each side: https://goo.gl/maps/a7jwnoVaqo9H4mRh7
- FR 55 has the same setup towards Pocahontas and Bath counties, bouncing back and forth along the ridge line
- Virginia SR 601 in Highland County rides the state line in some areas and actually crosses over entirely into WV in a couple spots.
- Virginia SR 616 follows the state line with McDowell County, WV for about 16 miles starting at WV/VA 83
- McDowell CR 83/9 and CR 83/10 follow the VA/WV state line for a couple miles north of WV/VA 83

[jay8g]

ID/WA 41 in Newport, WA/Oldtown, ID is an interesting case, where the Washington state route only exists to cover the Washington side of the road (which technically means it's a southbound-only highway for its entire 0.4-mile length). Supposedly, each half of the road is maintained by the respective state, but in practice it seems Idaho has been maintaining the entire thing (including a bridge replacement a few years back, which included street lighting installed on the Idaho side only).

[NWI_Irish96]

The entire length of IN 110 is on the Marshall/Fulton county border.
US 31 spends a few miles on the Fulton/Miami county border.
The entire length of the eastern IN 4 is on the Steuben/DeKalb county border.
IN 114 spends a few miles on the Wabash/Whitley county border.

[MATraveler128]

US 209 runs along the border of New Jersey from Bushkill to Matamoras.

NJ 29 follows the Pennsylvania border for its entire length.

[pderocco]

CA-161 runs along the Oregon border for almost 10 miles. Oddly, none of the side roads on the Oregon side have any "state line" signage. And there is a Welcome to California sign on OR-39 about 0.1 mile inside Oregon.

Also, UT-7 in St George dips down and runs along the Arizona border for about a mile.