Routes or roads you used to cross state lines.

[Flint1979]

Michigan to Ohio and back to Michigan using the same highways.

M-52 to OH-109 to OH-120 to turn around back to OH-109 back to M-52, then clinched all of M-52 to Saginaw.

[bing101]

I-80, I-15 and US-50 between California and Nevada

I-11 and US-93 between Arizona and Nevada.

[Takumi]

VA/NC: NC 615 (unnumbered on VA side), VA/NC 168, probably US 17, US 301, I-95, NC/VA 46, I-85, US 1, VA 4/NC 1xxx, possibly US 15, US 29, US 220, I-77.

VA/MD: US 301, I-495.

VA/DC: I-395/US 1, I-95/495 (I know), possibly I-66.

VA/WV, WV/MD: I-81

MD/PA: I-81, I-83

NC/SC, SC/GA, GA/FL: I-95

DC/MD: I-95/495, DC/MD 295

NC/TN: I-40, US 441

[hotdogPi]

VA/NC: NC 605 (unnumbered on VA side)

Wikipedia says that NC 605 only existed in the 1930s. Also, the number makes me think it would be VA SR 605 on the Virginia side.

EDIT: You might have meant 615, but I still wouldn't be surprised if it matches with a Virginia secondary of the same number.

[Takumi]

VA/NC: NC 605 (unnumbered on VA side)

Wikipedia says that NC 605 only existed in the 1930s. Also, the number makes me think it would be VA SR 605 on the Virginia side.

EDIT: You might have meant 615, but I still wouldn't be surprised if it matches with a Virginia secondary of the same number.

Yep. Brain fart. I meant 615. It used to be secondary on the Virginia side but has not been so since the 1960s. Not that that stops Virginia Beach from posting signs anyway.

[Mark68]

Unless otherwise noted, I have crossed both ways.

WA/ID: I-90 (to ID), US 12 (to WA)
WA/OR: I-5, I-205, I-82 (to WA)

OR/ID: I-84
OR/CA: I-5

CA/NV: I-80 (to NV), CA/NV 28, US 50 (to NV), US 395 (southern portion), I-15, US 95
CA/AZ: I-40

NV/AZ: NV 163/AZ 95, Hoover Dam (when US 93 crossed the dam--to NV), I-15
NV/UT: US 93 Alt (Wendover Blvd), I-80
NV/ID: US 93 (just to get to the casinos in Jackpot)

ID/UT: I-84

UT/WY: I-80, US 191 (to UT)
UT/CO: US 40 (to CO), I-70, US 491 (when it was 666--to CO), UT 162/CO 41 (to CO)
UT/AZ: US 163 (to UT), US 89A, UT 59/AZ 389 (to UT), I-15

AZ/NM: Four Corners Monument (parked on AZ side), I-40, NM 53/AZ 61 (to AZ)

NM/CO: US 160, US 550, US 285, CO 159/NM 522, I-25
NM/TX: US 87, I-40

CO/OK: US 385
CO/KS:  US 50 (into CO), I-70 (into KS)
CO/WY: US 85, I-25, US 287, WY 789/CO 13 (into CO)

WY/MT: I-90
WY/SD: I-90 (into SD), US 85 (into WY)

KS/MO: I-670
KS/OK: i-35 (into OK), US 270 (into KS)

OK/TX: US 287 (into OK)
OK/AR: I-40 (into AR)

TX/LA: I-20

LA/MS: US 90, I-10, I-20 (into MS)

AR/TN: I-55

TN/MS: US 72

MS/AL: US 72

AL/GA: US 278 (into AL), I-20 (into GA)

VA/DC: GW Pkwy, I-66

VA/WV: VA 9/WV 9 (to WV), i-81 (to VA)

WV/MD: US 11 (to MD), I-81 (to WV)

MD/PA: US 11 (to PA) to PA 163 (on border) to I-81 (back to MD)

MA/NH: MA 1A/NH 1A (into NH), I-95, I-93

NH/ME: US 1 Bypass (into ME), I-95 (into NH)

[dvferyance]

Colorado
I-25 WY SB
I-70 KS EB
I-76 NE WB
Connecticut
I-84 MA WB
I-95 NY SB
Florida
I-75 GA both
Georgia
I-24 TN both of them in both directions
I-75 FL and TN both
Illinois
IL-35 WI NB
IL-76 WI NB
IL-83 WI NB
IL-131 WI SB
US-12 WI SB
US-20 IA EB
US-45 WI NB
US-51 WI both
I-39/90 WI both
I-55/64 MO both
I-80 IA both
I-80/94 IN both
I-90 IN both
Indiana
CR-17 MI NB
IN-19 MI SB
I-65 KY both
I-70 OH both
I-74 OH both
I-80/90 OH both
I-80/94 IL both
I-90 IL both
I-275 KY and OH both
Iowa
US-20 IL EB
US-151 WI SB
I-35 MO NB
I-80 IL both and NE WB
Kansas
I-70 CO and MO EB
Kentucky
US-23 OH NB
I-64 WV both
I-65 IN and TN both
I-71/75 OH both
I-75 TN both
I-275 IN and KY both
Maryland
I-70 PA WB
I-81 PA and WV SB
I-495 VA NB
Massachusetts
I-84 CT WB
I-90 NY EB
Michigan
fmr M-205 IN SB
M-217 IN NB
I-94 IN both
Minnesota
I-90 SD amd WI WB
I-94 WI both
Missouri
I-35 IA NB
I-44 OK both
I-55/64 IL both
I-70 KS EB
Nebraska
I-76 CO WB
I-80 IA WB
New Jersey
I-80 PA WB
I-278 NY WB
New York
I-90 MA EB and PA both
I-95 CT SB
I-278 NJ WB
North Carolina
US-17 VA NB
US-220 VA SB
US-441 TN both
Ohio
US-23 KY NB
US-52 WV both
I-70 IN both
I-71/75 KY both
I-74 IN both
I-76 PA both
I-77 WV both
I-80 PA EB
I-80/90 IN both
I-90 PA both
Oklahoma
I-35 TX both
I-44 MO both
Oregon
I-5 WA both
Pennsylvania
I-70 MD WB
I-76 OH both
I-80 NJ and OH WB
I-81 MD SB
I-90 NY and OH both
South Dakota
US-18 WY WB
I-90 MN WB
Tennessee
US-441 NC both
I-24 GA both of them both directions
I-65 KY both
I-75 GA and KY both
I-81 VA NB
Texas
I-35 OK both
Virginia
US-17 NC NB
US-220 NC SB
US-460 WV both
I-64 WV both
I-81 MD SB and TN NB
I-495 MD NB
Washington
I-5 OR both
West Virginia
US-52 OH both
US-460 VA both
I-64 KY and VA both
I-77 OH both
I-81 MD and VA SB
Wisconsin
WI-31 IL SB
WI-35 IL NB
WI-83 IL NB
WI-140 IL NB
US-12 IL SB
US-45 IL NB
US-51 IL both
US-151 IA SB
I-39/90 IL both
I-90 MN WB
I-94 IL and MN both

[CNGL-Leudimin]

Given this thread has been revived, since I last posted I've added another crossing between Aragon and Navarre, from an unpaved road in Navarre into a paved one (CV-684) in Aragon. I've also crossed a regional line I had not done so before, from Castile la Mancha into the Valencian Community... but again, and like the crossings between Castile la Mancha and Andalusia I did so by high-speed train .

[sparker]

Continuing east to the Mississippi River (and St. Croix R. + extension):

LA/AR: US 71 (I-49 not yet constructed on that trip).
AR/MO: US 71, AR/MO 37, US 63, US 67.
MO/IA: I-29, US 61 (prior to AOS/MSR 27 construction).
SD/IA: I-29.
IA/MN: IA/MN 60.
LA/MS: I-10, I-59, I-20.
AR/TN: I-55, I-40.
MO/IL: US 60/62, I-57, I-255, I-55/64/former 70, McKinley Bridge, I-270, US 67.
IA/IL: US 34, I-280, I-80, US 20. 
MN/WI: US 14/61, I-90, I-94, US 8, I-535/US 53.

Adjoining states in covered areas that I've never traveled directly between (that have ways to cross, of course): AR to MS and IA to WI.

More to come easterly later.

[amroad17]

KY/OH: I-71/75, I-471, I-275, US 42/127, Roebling Suspension Bridge, Taylor-Southgate Bridge, Purple People Bridge, US 68, US 62, US 23, KY 10/OH 253, 13th St. Bridge (EB)
KY/IN: I-275, Markland Dam, US 421, I-65, I-64, US 231 (NB), US 41
KY/TN: I-75, US 25E, I-65, US 31W,  US 127, US 231 (NB), US 45/51/Purchase Parkway, I-24, US 79 (NB)
KY/WV: I-64
KY/VA: US 23

VA/NC: NC 615/former VA SSR 615, Blackwater Road, VA 168, US 17, former SSR 604-Desert Rd. (SB), VA 32, US 13, US 258, VA/NC 186, I-95, I-85, US 29, NC/VA 87, US 220, Blue Ridge Parkway (SB)
VA/MD: US 15, I-495, I-95/495, US 301 (SB), US 13
VA/WV: I-64, US 460, I-77/US 52, VA 598 (when it was US 52), US 219, US 522 (NB)

NY/PA: I-90, I-86, US 219, NY 16, US 15/I-99, US 220 (when it did go into NY), NY 34/PA 199, PA 29/NY 7 (NB), I-81, I-84

OH/IN: I-275, I-74, Harrison Ave., Lawrenceburg Rd., US 50, State Line Road, Carolina Trace Rd., OH 126/IN 252, OH 725/IN 44, US 27, OH 177/IN 227, I-70/US 35, US 40, US 33, US 30, US 6 (EB), I-80/90

[deathtopumpkins]

Starting from the northeast and roughly working my way southwest. I know I'm missing some non-numbered roads within New England. * indicates non-road land crossings.

NS/NB: TCH 2/104
NB/ME: NB 1, 95
ME/QC: 201/173
ME/NH: 1, 1 Bypass, 95, 101, 4, 9, 202, 109, 110, 153 (x2), 25, 302, 113 (x4), 113B (x2), 2, 26, 16, Amtrak*
NH/VT: Beecher Falls/Stewartstown bridge, VT 114, Columbia covered bridge, 105, 2, Mt Orne bridge, 18, 93, 302, 25, 113, 10A, 4, 89, Cornish-Windsor covered bridge, 12, 11, Arch bridge, 123, 9, 119
VT/QC: 91/55, 89/133
NH/MA: 1A, 286, 1, Main St, 95, 150, 107A, Bear Hill Rd, Highland Rd, Hadley Rd, W Hadley Rd, 108, 121A, 125, 121, 97, 28, 93, Cross St, Old Gage Hill Rd, Dutton Rd, 38, Mammoth Rd (128), Long Pond Rd, 3A, DW Hwy, 3, 111, 122, 13, 123, 124, 31, 123A, 119, 202, 12, 32, 78, 10, 63, Amtrak*
VT/MA: 142, 91, 112, 8A, Readsboro Rd/Tunnel St, 8, 7
QC/NY: 11/223, 87/15
VT/NY: 2, 17/185, 74 (ferry), 4, 22A, one of the Hampton/Poultney roads, 31, 149, 153, 313, 67, 279, 7/9, 346
MA/RI: 177, 81, 24, 138, 103, 136, 114A (x2), 6, 195, 44, 152, 15, 1A, 1, 95, 123, 295, 120, 121, 126, 122, 146, 146A, Douglas Pike, 98, 96, 100, Amtrak*, MBTA*
RI/CT: 44, 6, 14, 138, 95, 216, 78, 1, Amtrak*
MA/CT: 193, 395, 12, 197, 31, 131, 169, 198, 84, 19, 32, 83, 186, 220, 192, 5, 91, 159, 75, 187, 168, 202, 189, 8, 183, 7, 7A, 41
MA/NY: 2, 43, 20, 295, 102, 90, 71, 23, 344, Amtrak*
CT/NY: 44, 6/202, 84, 684 (x2), 120A, 15, 1, 95, Metro-North*, Amtrak*
NY/NJ: 440 (x2), 278, 78, 95, 9W, PIP, GSP, 202, 287, 210, Amtrak*, NJT*, PATH*
NY/ON: Lewiston-Queenston Bridge, Peace Bridge
NY/PA: 90, 86, 15, 17 (x2), 84
PA/NJ: 80, 22, 78, Milford Bridge, 202, 295, 1, 95, 676, Amtrak*, SEPTA*
NJ/DE: Delaware Memorial Bridge
PA/DE: 95
PA/MD: 1, 83, 15, 11, 81, 70, 220
PA/OH: 80, 90
PA/WV: 70
MD/WV: 68, 522, 81
MD/DE: 279, 95, 13, 113
MD/VA: 340, 15, 495, 301, 13
MD/DC: 50, 295 (x2), 95/495
DC/VA: 395, 95/495, WMATA*
WV/OH: 70
WV/KY: 64
VA/NC: 615, 168, 17, 32, 13, 258, 186, 95, 85, 15, 501, 86
VA/WV: 340, 81, 522
VA/TN: 81
NC/TN: 40
NC/SC: 95
SC/GA: 95, 17
GA/FL: 95
TN/GA: 24
GA/AL: 59
AL/MS: 20/59
MS/LA: 59
TN/AR: 40
IN/KY: 64
IN/OH: 20, 80/90, 6, 24, 30, 70
MI/ON: Ambassador Bridge, Blue Water Bridge
MI/IN: 94
IL/IN: 90, 80/94, 30, 70, 64
MO/IL: 255, 55/64, 70
IA/IL: 280
WI/IL: 94
WI/MI: 41
IA/NE: 80
KS/MO: 670, 400
KS/OK: 69 Alt
OK/MO: 44
OK/AR: 40
CO/NE: 76
CO/KS: 70
TX/OK: 40
NM/TX: 40

[CoreySamson]

Okay here goes.

Asterisk means I traveled as a passenger.

TX/AR: I-30, Loop 151*, State Line Avenue (Crossed over to get to a Wendy's on the other side of the road)

TX/LA: I-10*

LA/MS: I-10*, I-55*

AR/TN: I-40, Big River Crossing (walked)

TN/MS: I-55*

MS/AL: I-10*

AL/FL: I-10*

I also went to the Carolinas via Georgia when I was little, but not sure what route my family took. My list is sparse because I'm the only one in my family who likes road trips.

Also very odd that the state line I've crossed in the most places is TX/AR.

[NWI_Irish96]

Updated:

Just going to list my ones for Indiana. I've left/entered Indiana on 90 different roads.

IN/IL (33)
I-90 Indiana Toll Road/Chicago Skyway
US 12/20/45 Indianapolis Blvd
Gostlin St/Brainard Ave
Sibley Blvd
Wildwood Rd/Michigan City Rd
165th St/River Oaks Dr
River Dr/Bernice Rd
I-80/94/US 6
Adelaide Pl/177th St
Ridge Rd
Terrace Dr
45th St/Glenwood-Lansing Rd
US 30
IN 2/IL 17
IN 10/IL 114
US 24/52
IN 18/CR 880N
IN 26/IL 9
IN 28/IL 119
US 136
I-74
IN 32/Perrysville Rd
IN 234/Mill Rd
US 36
IN 163/Clinton Rd
US 150
I-70/US 40
IN 154/Clover St
US 50
IN 441/Old US 50
IN 64/IL 15
I-64
IN 62/IL 141

IN/KY (12) [have completed all of these]:
US 41
IN 161/KY 2262
US 231
IN 237/KY 69
IN 135/KY 79
I-64
US 31
I-65 (both bridges)
IN 265/KY 841
US 421
IN 101/KY 1039
I-275

IN/OH (27)
I-275
US 50
I-74/US 52
IN 242/OH 126/129
US 27
IN 44/OH 725
IN 227/OH 177
I-70
US 40
IN 121/New Paris Rd
US 36
IN 28/OH 571
IN 32/OH 47
IN 26/OH 119
IN 67/OH 29
IN 218/OH 707
IN 124/OH 81
US 33
US 224
US 30
US 24
IN 37/OH 2
IN 8/OH 18
US 6
IN 427/OH 34
I-80/90
US 20

IN/MI (18)
IN 120/Territorial Rd
Fremont Rd
I-69
IN 327/Rierson Rd
IN 9/M-66
US 131
IN 15/M-103
CR 17/M-217
IN 19/Cassopolis Rd
IN 23/M-62
Gumwood Rd
Ironwood Rd
IN 933/M-51
US 31
IN 39/M-239
I-94
US 12
Lake Shore Dr

[CNGL-Leudimin]

I've since added other two crossings between Aragon and Navarre: A/NA-137 and A/NA-176. In all I've crossed that regional limit in all but three local roads in the Southern part.

[Bruce]

Copying from the other thread, and including all modes:

14 - WA/ID (car only): Southway Bridge, US 12, SR 128/ID 128, US 195, US 195 Spur, SR 270/ID 8, ID 66, SR 272/ID 6, SR 274/ID 60, SR 278/ID 58, I-90, SR 290/ID 53, ID 41, US 2
11 - WA/OR (mostly car): US 101, SR 433, I-5 (car and foot), I-205, Bridge of the Gods (foot), Hood River Bridge/OR 35, US 197, US 97, I-82, US 730, SR 125/OR 11
6 - MD/DC (rail, bike, bus, and foot): WMATA Blue/Silver Line, WMATA Orange Line, WMATA Green/Yellow Line, WMATA Red Line West, WMATA Red Line East, US 1
3 - VA/DC (rail and bike): WMATA Blue/Orange/Silver Line, WMATA Green/Yellow Line, I-66
2 - OR/ID (car only): I-84, US 30
2 - ID/MT (car only): US 2, ID 200/MT 200
2 - NY/CT (bus only): I-684, I-84
1 - MI/OH (car only): I-75
1 - NJ/NY (rail only): PATH
1 - CT/MA (bus only): I-84
1 - VA/MD (bus only): I-495

For Canada:

6 - WA/BC (car, rail, bus, foot) - Point Roberts, Amtrak Cascades, Peace Arch, I-5, SR 543/BC 15, SR 539/BC 13
2 - ON/QC (rail and bus) - VIA Rail, ON 417/QC A-40
1 - MI/ON (car and bus) - Detroit-Windsor Tunnel

[SkyPesos]

There's 2 of these threads? Anyways, copying and pasting whatever I have in the other thread, minus the non-road crossings. Note that it includes Canadian provinces.

BC/WA (I-5/BC 99)
CT/MA (I-84), CT/NY (I-95)
DC/MD (SR 295), DC/VA (I-395)
DE/MD (I-95), DE/NJ (I-295)
FL/GA (I-75)
GA/TN (I-75)
IL/IN (I-64, I-70, I-80/94, I-90), IL/MO (I-55/64, I-70, I-270, MLK Br), IL/WI (I-39/90)
IN/KY (I-64, I-265, I-275), IN/OH (I-70, I-74, I-275)
KS/MO (I-35)
KY/OH (I-71/75, I-275, I-471, Roebling Br), KY/TN (I-65, I-75)
MD/PA (I-70, US 40), MD/VA (I-495, US 15)
MI/OH (I-75), MI/ON (I-69/94/ON 401)
MN/WI (I-94)
NJ/NY (I-78, I-95, I-278, Lincoln Tun), NJ/PA (I-78, I-80)
NY/ON (Rainbow Br), NY/PA (I-90)
NC/SC (I-26, I-77), NC/TN (I-40), NC/VA (I-77)
OH/PA (I-76, I-80, I-90), OH/WV (I-70, I-470, US 22, US 35)
PA/WV (I-70, US 22)

[US 89]

Alright, here goes. This should be a comprehensive list, by state entered and in a clockwise direction:

Alabama
-MS: I-22
-TN: AL 53 (western), TN 377/AL 73
-GA: GA 301/Jackson CR 90, I-59, GA 48/AL 117, GA 337/Cherokee CR 99, US 278, I-20, GA 34/AL 22, US 80, GA 39 Spur/AL 208

Arizona
-NV: I-15
-UT: I-15, UT 59/AZ 389 (?), US 89, US 163
-NM: US 160

Arkansas
-OK: OK 112/Y St, OK 20/AR 43
-MO: MO/AR 43, US 63
-TN: I-40

California
-NV: I-80

Colorado
-UT: US 491, I-70, US 40
-WY: WY 789/CO 13, US 287, I-25
-OK: US 287/385, unnamed road to CO/NM/OK tripoint
-NM: US 84, US 550, US 491

District of Columbia
-VA: I-395/US 1, US 29

Florida
-AL: US 231

Georgia
-AL: US 80, I-85, AL 22/GA 34, I-20, Cherokee CR 99/GA 337, AL 117/GA 48, AL 71/GA 136
-TN: I-24 (west), TN 134/GA 299, I-24 (east), I-75, US 41/76, US 411
-NC: NC 69/GA 17-515, NC 175/GA 75
-SC: I-85, US 29, US 378, I-520, US 17

Idaho
-OR: I-84
-MT: I-15, US 20
-WY: WY 22/ID 33, US 89, WY 89/ID 61
-UT: US 89, US 91, UT 200/State St, UT 61/Franklin CR D1, I-15, I-84, UT 42/Old ID 81

Illinois
-MO: I-70, I-270
-WI: WI 31/IL 131

Indiana
-KY: I-65

Iowa
-NE: I-80
-SD: US 18

Kansas
-CO: I-70
-MO: I-35, 50th St

Kentucky
-IL: I-24
-IN: US 31

Maine
-NH: probably I-95

Maryland
-DC: Wisconsin Ave/MD 355

Massachusetts
-NH: probably I-95

Mississippi
-TN: I-55/69

Missouri
-IA: I-29
-IL: I-55/64
-AR: AR/MO 43
-OK: OK 10/Secondary O
-KS: I-70

Montana
-WY: North Entrance Rd (implied US 89), US 191 (both)
-ID: US 20, I-15

Nebraska
-WY: I-80

Nevada
-UT: UT 30/NV 233, I-80, US 6/50
-AZ: I-15
-CA: I-80

New Hampshire
-ME: probably I-95
-MA: probably I-95

New Mexico
-AZ: US 64
-CO: US 160, US 491, I-25
-OK: Rinker Rd
-TX: US 87, US 70/84

North Carolina
-SC: S-26-33/Fronis Strickland Rd, I-77
-GA: US 19/129, GA 60 Spur/NC 60
-TN: US 64/74

Oklahoma
-CO: unnamed road from CO/NM/OK tripoint
-KS: US 75
-AR: AR 43/OK 20, I-40, US 271
-NM: US 56/64/412, NM 456/OK 325

Oregon
-ID: I-84
-WA: I-82

South Carolina
-GA: I-95, US 1/25/78/278, I-20, US 123, US 76
-NC: NC/SC 51, Hickman Rd/S-26-57

South Dakota
-IA: US 18

Tennessee
-AR: I-55
-KY: I-24
-GA: US 411, I-75, GA 189/TN 148, US 11, I-24 (east), I-24 (west)
-AL: AL 73/TN 377, I-65

Texas
-OK: I-40

Utah
-NV: NV 487/UT 21, BL-80/UT 58, I-80
-ID: Old ID 81/UT 42, I-84, Old Highway 191, I-15, Franklin CR D1/UT 23, State St/UT 200, US 91, US 89
-WY: WY 89/UT 30, I-80, UT 43 (west)
-CO: US 40, I-70, US 491
-AZ: US 163, US 89, AZ 389/UT 59 (?), I-15

Virginia
-DC: I-395/US 1

Washington
-OR: I-82

Wisconsin
-IL: I-41/94

Wyoming
-ID: US 30, US 89 (?), ID 34/WY 239,  Ski Hill Rd
-MT: West Entrance Rd (implied US 20/191/287), US 191 (both), North Entrance Rd (implied US 89)
-CO: CO 125/WY 230, CO 13/WY 789
-UT: US 191, UT/WY 150, I-80, UT 16/WY 89, UT 30/WY 89

[JayhawkCO]

Only using state highway level and above, otherwise KC alone would add another 80-100.  232 total.

AL-FL   I-10   US231                           
AL-GA   I-20   I-59   US280                       
AL-MS   I-10   I-20/59 I-22   US45                       
AL-TN   I-65                                                               
AZ-NV   I-15   US93                           
AZ-NM   I-10   I-40   US160                       
AZ-UT   I-15   US89A  AZ389/UT59
AR-LA   I-49                     
AR-MO   I-55   US63  US71                       
AR-TN   I-40   I-55   
AR-TX   I-30                     
CA-NV   I-15   I-80                           
CO-KS   I-70   US36  US40  CO96/KS96                     
CO-NE   I-76   US6   US34  US138  US385   CO11/NE27  CO23/NE23  CO113/NE19         
CO-NM   I-25   US84  US160 US285 US550 CO159/NM522 CO140/NM140 CO172/NM511 CO389/NM551                     
CO-OK   US287/385                             
CO-UT   I-70   US40  US491 CO90/UT46  CO318/Brown's Park Road                       
CO-WY   I-25   US85 US287  CO13/WY789    CO125/WY230   CO127/WY230 WY70 WY70
CT-MA       I-91
CT-NY   I-84                             
CT-RI   I-95                             
DE-MD   I-95   US113 DE16/MD16                           
DE-NJ   I-295
DE-PA       I-95                             
DC-MD   I-295  I-95/495    DC295/MD295                       
DC-VA   I-66   I-95/495  I-395                       
FL-GA   I-75   I-95                           
GA-SC   I-95                             
GA-TN   I-24   I-24   I-75                       
ID-MT   I-15   I-90   US93  ID200/MT200                     
ID-OR   I-84                             
ID-UT   I-15   I-84   US91                       
ID-WA   I-90                             
ID-WY   US30  ID16/WY89   ID30/WY89  ID33/WY22                         
IL-IN         I-64  I-70   I-74   I-80/94 I-90                 
IL-IA         I-74 I-80 I-280                             
IL-KY   I-24                             
IL-MO   I-55/64  I-57  I-70  I-72  I-255  I-270               
IL-WI   I-39/90  I-41/94                           
IN-KY   I-64   I-65   US41                       
IN-MI   I-94                             
IN-OH   I-70   I-74 I-80/I-90                           
IA-MN   I-35   US52                           
IA-MO   I-29   I-35                           
IA-NE   I-80   I-680                           
IA-SD   I-129                             
KS-MO   I-35   I-70   I-435  I-435  I-635  I-670  US36    US56  US59  US69  KS92/MO92
KS-NE   US73/159   KS7/703 Trail                           
KS-OK   I-35   US169                           
KY-OH   I-71/75                             
KY-TN   I-24   I-65   I-75                       
KY-WV   I-64                             
LA-MS   I-10   I-20   I-55   I-59                     
LA-TX   I-20                             
ME-NH   I-95 US302                           
MD-PA   I-70 I-83                             
MD-VA   I-495  I-495 US13
MD-WV   I-68 I-81                     
MA-NH   I-93   I-95
MA-NY       I-90                           
MA-RI   I-95     
MA-VT       I-91                       
MN-ND   I-94   I-94BL                           
MN-SD   I-90                             
MN-WI   I-90   I-94   I-535  US10  US63  MN36/WI64   MN60/WI25           
MS-TN   I-55   US78                           
MO-NE   US159                             
MO-OK   I-44                             
MO-TN   I-155                             
MT-ND   I-94                             
MT-WY   I-90   US212                           
NE-WY   I-80   US30 WY151/NE88 WY216/State Line Road               
NV-UT   I-80                             
NH-VT   I-89 I-93 US2 NH9/VT9 NH10A/VT10A                             
NJ-NY   I-78   I-95 I-287                           
NJ-PA   I-76 I-78   I-80   I-95 I-295   I-676                     
NM-OK   US56/64/412                             
NM-TX   I-10   I-40   US60/70/84  I-40BL
NY-PA        I-81                                                   
NC-SC   I-26   I-77   I-95   US1                     
NC-TN   I-26                             
NC-VA   I-77   I-85 I-95                           
ND-SD   I-29   
OH-PA   I-76                       
OH-WV   I-70                             
OK-TX   I-35   I-40   I-44                       
OR-WA   I-5  I-82  I-205  US730                     
PA-WV   I-70 I-79                             
SD-WY   I-90                             
UT-WY   I-80                             
VA-WV   I-77     

Chris

[kurumi]

I'll limit this just to crossing on a bicycle (expanding this would make a fine bucket list)

CT-MA: US 5. About a 65-mile trip when I was a teenager. Crossing the state line was definitely the objective.

CA-NV: SR 28. This was a group ride all the way around Lake Tahoe, clockwise (89/28/50). Beautiful ride.

[Skye]

OH/IN: I-275, US 50, various streets in Harrison/West Harrison, I-74, OH 126/IN 252, US 27, various streets between Harrison and College Corner, I-70

OH/KY: all greater Cincinnati bridges, US 62 Bus (Maysville, KY), OH 852, US 23

OH/WV: US 52

OH/PA: I-90, I-80

KY/IN: I-275, I-64

PA/NY: I-90

PA/NJ: I-80

NJ/NY: I-287, Lincoln Tunnel

KY/TN: I-75

TN/GA: I-75

GA/FL: I-75, I-95

GA/SC: I-95

TN/NC: I-40, I-81, US 441

NC/SC: I-26, I-77, I-95, US 17, 905, 179

NC/VA: I-77

VA/WV: I-77

VA/KY: I-64

IN/IL: I-80/94, I-90

IL/WI: I-94

[RoadRebel]

I live near the Carolina border and cross it all the time. Many crossings are on roads with no highway numbers. As for numbered routes:

US-17
I-77/US-21
US-321
US-521
US-601
NC-49/SC-49
NC-51/SC-51
NC-75/SC-75
NC-160/SC160
NC-161/SC-161
NC-179/SC-179
NC-274/SC-274
NC-279 (No matching SC continuation)

NC/Tennessee:
US-19E

SC/Georgia and Georgia/Florida:
I-95 (Passenger)

[Mark68]

Unless otherwise noted, I have crossed both ways.

WA/ID: I-90, US 12 (to WA)
WA/OR: I-5, I-205, I-82 (to WA)


OR/ID: I-84
OR/CA: I-5

CA/NV: I-80 (to NV), CA/NV 28, US 50 (to NV), US 395 (southern portion), I-15, US 95
CA/AZ: I-40

NV/AZ: NV 163/AZ 95, Hoover Dam (when US 93 crossed the dam--to NV), I-15
NV/UT: US 93 Alt (Wendover Blvd), I-80
NV/ID: US 93 (just to get to the casinos in Jackpot)

ID/UT: I-84

UT/WY: I-80, US 191 (to UT)
UT/CO: US 40 (to CO), I-70, US 491 (when it was 666--to CO), UT 162/CO 41 (to CO)
UT/AZ: US 163, US 89A, UT 59/AZ 389 (to UT), I-15

AZ/NM: Four Corners Monument (parked on AZ side), I-40, NM 53/AZ 61 (to AZ)

NM/CO: US 160, US 550, US 285, CO 159/NM 522, I-25
NM/TX: US 87, I-40

CO/OK: US 385
CO/KS:  US 50 (into CO), I-70 (into KS)
CO/WY: US 85, I-25, US 287, WY 789/CO 13 (into CO)

WY/MT: I-90
WY/SD: I-90 (into SD), US 85 (into WY)

KS/MO: I-670
KS/OK: i-35 (into OK), US 270 (into KS)

OK/TX: US 287 (into OK)
OK/AR: I-40 (into AR)

TX/LA: I-20

LA/MS: US 90, I-10, I-20 (into MS)

AR/TN: I-55

TN/MS: US 72

MS/AL: US 72

AL/GA: US 278 (into AL), I-20 (into GA)

VA/DC: GW Pkwy, I-66

VA/WV: VA 9/WV 9 (to WV), i-81 (to VA)

WV/MD: US 11 (to MD), I-81 (to WV)

MD/PA: US 11 (to PA) to PA 163 (on border) to I-81 (back to MD)

MA/NH: MA 1A/NH 1A (into NH), I-95, I-93

NH/ME: US 1 Bypass (into ME), I-95 (into NH)

Adding:

NV/AZ: US 93/I-11 (O'Callaghan/Tillman Bridge--to NV)

[RoadRebel]

I live near the Carolina border and cross it all the time. Many crossings are on roads with no highway numbers. As for numbered routes:

US-17
I-77/US-21
US-321
US-521
US-601
NC-49/SC-49
NC-51/SC-51
NC-75/SC-75
NC-160/SC160
NC-161/SC-161
NC-179/SC-179
NC-274/SC-274
NC-279 (No matching SC continuation)

NC/Tennessee:
US-19E

SC/Georgia and Georgia/Florida:
I-95 (Passenger)

Recent Additions:

NC/Tennessee:
US-321

NC/SC
NC-207/SC-207
NC-522/SC-522

[fwydriver405]

Comprehensive list as of 7 March 2022 (marked with *)

ME/NB, CAN
I-95/NB 95

ME/NH
US Route 1 Bypass (Both new and old Sarah Long Bridge, driven and biked across)
US Route 1 (New Memorial Bridge, driven and biked across)
I-95 (Piscataqua River Bridge)
ME Route 103
ME / NH Route 4
ME / NH Route 9
Rochester St (Berwick ME) / Salmon Falls Rd (Somersworth NH)
US Route 202
Water St (Milton Mills NH) / Foxes Ridge Rd (Acton ME) (entering ME)
Church St (Milton Mills NH) / Milton Mills Rd (Acton ME) (entering NH)
ME / NH Route 109
ME / NH Route 110 (entering NH)
ME / NH Route 25 (entering ME)
US Route 302
US Route 2 (entering NH)

NH/MA
US Route 1 (entering MA)
I-95
NH / MA Route 125
NH / MA Route 28
I-93
Middlesex Rd (Tyngsborough MA) / D W Highway (Nashua NH)
US Route 3 / Everett Turnpike (Nashua NH)

NH/VT
I-89
I-93 (entering NH)
US 2

MA/RI
I-95
I-195 (entering RI)

MA/CT
I-395
I-84
I-91 (entering CT)
CT / MA Route 159 (entering CT, bus took a wrong turn on a HS field trip)
CT / MA Route 75

MA/NY
I-90 (Mass. Pike / NY State Thruway Berkshire Connector)

RI/CT
I-95 (entering RI)

CT/NY
I-84*
I-95
I-684*
CT Route 15 (Merritt Pkwy) / Hutchinson River Pkwy (entering NY)
Bridgeport - Fort Jefferson Ferry (some trips from UMaine to Stony Brook NY)

NY/NJ
I-287 (entering NJ)
George Washington Bridge (I-95, US Route 1-9 and 46)
Lincoln Tunnel (NJ / NY Route 495) (entering NY)
I-78 (Holland Tunnel)
Garden State Parkway (NJ Route 444/NY Thruway Connector)*

NJ/PA
I-78 (Delaware River Bridge)

VA/DC
I-395 via the 14th ST and Rochambeau Bridge*
WMATA Yellow Line from Arlington VA

DC/MD
Pennsylvania Ave (MD Route 4 on the MD side)*
Baltimore-Washington Pkwy into DC*

NC/VA
I-77 (entering VA) (New 2021-11-08)

[ctkatz]

every time I have crossed a state line has been on an interstate except for:
ky-in us 31*
ky-oh us 42/127/25*
tn-al tn 7/al 53
al-ms-tn us 78 (at the time proto I 22)
sd-wy-mt us 212
va-md us 13*
md-de us 113*
in-il us 30
in-oh us 36

it's not like I don't like the scenic routes, it's just that I much rather prefer no detours and to stay on the main road. in fact if I planned the route I stick to the interstate, if I'm going off the interstate usually it's because I'm not the one driving or there's something off the road I wanted to see.  that 5 of these crossings happened when I was a passenger speaks to this.