Routes that parallel state borders

[sandiaman]

NM 9 crawls across  the  Bootheel  of  NM,  much  of  it  close  to  the Mexican  border.  AZ  80  hugs  the  Mexican  border  from Douglas  to Bisbee.  AZ  95  follows  the  California  border  for  most  of  its  route.

[roadman65]

US 5 and I-91 are pretty close to the NH State Line (Connecticut River) from the MA Line to St. Johnsbury, VT. 

US 3 travels about 30 or so miles on the east side of the Connecticut River in NH after US 5 and I-91 part ways on the other side in Vermont.

Does not the I-80/90 Toll Road in Indiana follow close to the MI state line for over 100 miles or more?

[JCinSummerfield]

Yes on I-80/90, being within eyeshot of Michigan.  Also, don't forget about OH-7, running along Ohio's SE & E border.

[hotdogPi]

US 5 and I-91 are pretty close to the NH State Line (Connecticut River) from the MA Line to St. Johnsbury, VT.

That was mentioned in the original post!

[cpzilliacus]

I-68 in West Virginia and Maryland runs close to, but never enters, Pennsylvania.

[agentsteel53]

I-68 in West Virginia and Maryland runs close to, but never enters, Pennsylvania.

similarly, US-18 never enters Nebraska.

US-52, however, does enter Kentucky.

[JMoses24]

HB mentioned KY 8.

US 50 parallels the Kentucky state line for a period from south of the junction with Ohio SR 125, through downtown Cincinnati, out to just south of Ohio SR 128 near Cleves, Ohio. If we ignore that deviation to the north (it only lasts about a mile or so), then US 50 can be said to parallel the KY state line into Indiana to just outside of Aurora, Indiana, where it finally leaves the Ohio River behind for good.

[SD Mapman]

similarly, US-18 never enters Nebraska.

But it gets really close.

[myosh_tino]

CA-161 between US 97 and CA-139

https://www.google.com/maps?ll=41.972764,-121.714783&spn=0.311402,0.449066&t=m&z=11

[hbelkins]

Two that just popped into my mind after reading the links in the WV railroad vs. log truck thead. WV 90 and WV 24. Both parallel the Maryland state line.

[Thing 342]

US 58 never gets more than about 20 miles from the VA-NC-TN border throughout its 508-mile length.

[thenetwork]

SR-184 (Alexis Road) is the last major east-west highway in Toledo before you cross into Michigan.  Most, if not all of SR-184 is less than 3/4-miles from the border.

[TCN7JM]

I-29 in Nebraska, and across the border, US 75

Other way around. I-29 is on the Iowa side, US-75 crosses the border in Sioux City and parallels the river on the Nebraska side from there south.

Apologies if this has already gotten a mention, but Iowa Highway 9 parallels the Minnesota state line.

[NE2]

US 460 between Petersburg and Suffolk parallels the south part of the Nevada-California border.

[cpzilliacus]

Two that just popped into my mind after reading the links in the WV railroad vs. log truck thead. WV 90 and WV 24. Both parallel the Maryland state line.

Especially W.Va. 90 (because it's longer than W.Va. 24, though not especially long).  It runs through mostly wild and undeveloped (but frequently mined-out) lands from U.S. 219 relatively close to the upper reaches of the Potomac River and ends a stone's throw from the Potomac just east of Bayard at U.S. 50.

[Buck87]

US 52 closely hugs the Ohio River from downtown Cincinnati until it finally crosses it into Huntington WV. It covers about 90% of the OH/KY border.

OH 49 follows the Indiana border from Greenville to the Michigan line where it becomes M 49. It covers about 2/3 of the OH/IN border.

The OH/MI border is really all that extensive, but it does have US 20 following it pretty closely most of the way.

The Lake Erie shoreline isn't really a border, but if we want to count routes following a states outline then OH 2 would get the nod here for covering most of that.

And as mentioned previously, OH 7 is the king of border roads in Ohio, covering pretty much the entire WV and PA borders.

[national highway 1]

I-8, CA 94 and CA 98 parallel the California-Mexico Border.

[US81]

What about ON the border, as US 71 thru Texarkana? TX and AR.