Which long haul interstate shares the least amount of pavement?

[OCGuy81]

As the interstates gradually replaced their US highway counterparts, which of the "long haul" interstates (I-x0 or I-x5) share the least amount of pavement with other highways? 

For example, Interstate 5. Mileage is approximate:

- Concurrent with US-12 in Washington (20 miles)
- Concurrent with US-30 in Portland, OR (1 mile)
- Concurrent with OR-99E in Oregon (24 miles)
- Concurrent with OR-99 at various points between Eugene-Ashland (100 miles)
- Concurrent with CA-99 in Sacramento (7 miles)
- Concurrent with CA-33 in the Central Valley (12 miles)
- Concurrent with I-10 in LA (1 mile)

Might be missing some here, but of I-5's 1,381 miles, it only shares pavement for roughly 165 miles, or 12% of its length.

I feel the western interstates will be the winners in sharing the least amount of pavement.

[Evan_Th]

Are we going by miles, or percentage of overall length?  If the first, then I-45 is a reasonable candidate just because it's so short.  I count 53 miles of overlap there:  25 with US 90 + 28 with US 287.

[NWI_Irish96]

I-65 has surprisingly little:

AL 10Tr 2.4 miles
US 80/AL 8 1.1 miles
US 82/AL 6 10.7 miles
AL 14 2.3 miles
US 31/AL 3 3.0 miles
AL 69 4.0 miles
US 31 6.8 miles
I-40 3.0 miles
I-24 2.0 miles
KY 61 0.2 miles
I-70 1.5 miles

That's a total of 37.0 out of 887.3 miles, or 4.17%

[OCGuy81]

Are we going by miles, or percentage of overall length?  If the first, then I-45 is a reasonable candidate just because it's so short.  I count 53 miles of overlap there:  25 with US 90 + 28 with US 287.

I was thinking of excluding the short ones (30 and 45) but we can go by overall percentage.

[jp the roadgeek]

I-95 has very little as well

FL (not including the SR designation): Brief concurrency with US 1 at the southern end (2.03 mi), concurrencies with US 1, US 17, and US 90 in Jacksonville (4 mi of concurrencies)

GA (not including the SR designation): None
SC: US 17 (10.6 mi), US 15/301 (5.1 mi)
NC: US 301 (11.13 mi)
VA: US 460 (2.82 mi), I-64 (3.29 mi), US 1/US 17 (7.24 mi), I-495 (6.6 mi)
DC: I-495 (0.11 mi )
MD: I-495 (26.11 mi)
DE: US 202 (6.51 mi)
PA: US 322 (0.87 mi)
NJ: US 1/US 9/US 46 (1.32 mi)
NY: US 1/US 9 (2.66 mi to the end of the US 1 concurrency)
CT: US 1 (2 concurrencies totaling 3.1 mi)
RI: US 6 (about 0.75 mi), US 1 (1 mi)
MA: MA 128 (37.9 mi).  Included within the MA 128 concurrency is one with US 1 (2.38 mi) and another with US 3 (1.69 mi)
NH: None
ME: ME 15 (2.92 mi)

Of the 1908.48 miles, only 136 miles (7.13%) is concurrent with another route.  If you eliminate the I-495 DC beltway and MA 128 concurrencies (exclusive of the US 1 and US 3 concurrencies within the latter), the total drops to 69.4 mi (3.64 %). 

[roadman65]

Georgia has US 278 on I-20 from Lithia to Covington.
US 17 overlaps I-16 in Savannah.
US 41 on I-75 near Valdosta.

In NJ you have 15 miles of US 22 on I-78.

[SkyPesos]

For I-75, excluding the hidden designations of FL 93 and GA 401:

FL (0/470.88 mi, 0%): No concurrencies
GA (32.5/355.11 = 9.15%): US 41 (7 mi), GA 540 (16 mi), I-85 (8 mi), GA 5 (1.5 mi)
TN (36.5/161.86 = 22.55%): US 11/US 64 (4 mi), I-40 (17 mi), I-275 (3.5 mi), US 25W (5.7 mi), TN 63 (6.3 mi)
KY (27.3/191.78 = 14.24%): US 25/421 (1.5 mi), I-64 (6.8 mi), I-71 (19 mi)
OH (6.8/211.30 = 3.22%): I-71 (0.5 mi), US 27/52 (1 mi), OH 4 (2 mi), OH 15 (2.1 mi), US 23 (1.2 mi)
MI (85.5/395.54 = 21.62%): US 23 (73.5 mi), M-55 (12 mi)

Total: 188.6/1786.47 = 10.56% concurrent with another route. Much higher compared to its peer x5, I-65 and I-95, mentioned earlier in the thread.

I think the "loser" of this thread for long interstates might be I-25 or I-70. Unlike some other x0, like I-90, I-80 and I-40, I-70 doesn't have a US route truncated because of it, and that it's shorter than those three x0 mentioned, so percentage wise, it's going to be higher.
UT (208.5/232.15 = 89.91%): US 89 (33.5), US 50 (175), with US 6 joining in the middle of the US 50 overlap
CO (261.5/449.59 = 58.16%): US 6/US 50 (11.1), US 6 (18), US 6 (5.3), US 6 (23.2), US 6 (34.3, includes SH 9 concurrency), US 6 (28.1, includes US 40 concurrency), US 40 (2.2), US 6/US 85 (2), US 36 (36.8), US 40/287 (47.1, portion of concurrency counted under US 36), US 24 (42), US 24 (11.4)
KS (391.8/422.82 = 92.66%): US 24 (45.8), US 40 (329.5, includes concurrencies with K-14, K-18, K-4 and US 75), US 24/US 40 (16.5, includes concurrencies with US 69 and US 169)
MO (174.2/250 = 69.68%): US 40 (7, includes concurrencies with US 24, US 169, I-35 and US 71), US 40 (77.4), US 40 (89.8)
IL (29.7/155.74 = 19.07%): I-55 (16.1, includes concurrency with US 40), US 40 (5.6), I-57 (6.2), US 40 (1.8)
IN (20.6/156.6 = 13.15%): US 40 (11.2), I-65 (1.5), US 35 (7.9)
OH (29.3/225.6 = 12.99%): US 35 (1.8), OH 49 (1.2), OH 4 (6.3), I-71 (2), US 40 (18)
WV (1.3/14.45 = 9%): US 250 (1.3, includes US 40 concurrency)
PA (92.4/167.92 = 55.03%): I-79 (3.5), I-76 (86), US 30 (0.3), US 522 (2.6)
MD (38/93.62 = 40.59%): US 522 (1), US 40 (8), US 40 (29)

Total: 1247.3/2151.43 = 57.98% concurrent with another route.

[hotdogPi]

Related thread (Overlap Averages): near-same calculations*, different goals

*multiple overlaps count multiple times in the thread linked and only once in this thead

[OCGuy81]

I looked at I-15 as well.  There's a decent amount of concurrencies overall, but all are fairly short.

-NV (21 miles with US-93)
-UT (9 miles with US-50, 10 miles with US-6, 17 miles with US-89, 3 miles with I-80, 38 miles with I-84)
-ID (30 miles with US-91)
-MT (8 miles with I-90, 35 miles with US-287, 11 miles with US-89)

Of the 1,433 miles, there's 182 miles concurrent, or 12.7%

[roadman65]

For I-75, excluding the hidden designations of FL 93 and GA 401:

FL (0/470.88 mi, 0%): No concurrencies
GA (32.5/355.11 = 9.15%): US 41 (7 mi), GA 540 (16 mi), I-85 (8 mi), GA 5 (1.5 mi)
TN (36.5/161.86 = 22.55%): US 11/US 64 (4 mi), I-40 (17 mi), I-275 (3.5 mi), US 25W (5.7 mi), TN 63 (6.3 mi)
KY (27.3/191.78 = 14.24%): US 25/421 (1.5 mi), I-64 (6.8 mi), I-71 (19 mi)
OH (6.8/211.30 = 3.22%): I-71 (0.5 mi), US 27/52 (1 mi), OH 4 (2 mi), OH 15 (2.1 mi), US 23 (1.2 mi)
MI (85.5/395.54 = 21.62%): US 23 (73.5 mi), M-55 (12 mi)

Total: 188.6/1786.47 = 10.56% concurrent with another route. Much higher compared to its peer x5, I-65 and I-95, mentioned earlier in the thread.

I think the "loser" of this thread for long interstates might be I-25 or I-70. Unlike some other x0, like I-90, I-80 and I-40, I-70 doesn't have a US route truncated because of it, and that it's shorter than those three x0 mentioned, so percentage wise, it's going to be higher.
UT (208.5/232.15 = 89.91%): US 89 (33.5), US 50 (175), with US 6 joining in the middle of the US 50 overlap
CO (261.5/449.59 = 58.16%): US 6/US 50 (11.1), US 6 (18), US 6 (5.3), US 6 (23.2), US 6 (34.3, includes SH 9 concurrency), US 6 (28.1, includes US 40 concurrency), US 40 (2.2), US 6/US 85 (2), US 36 (36.8), US 40/287 (47.1, portion of concurrency counted under US 36), US 24 (42), US 24 (11.4)
KS (391.8/422.82 = 92.66%): US 24 (45.8), US 40 (329.5, includes concurrencies with K-14, K-18, K-4 and US 75), US 24/US 40 (16.5, includes concurrencies with US 69 and US 169)
MO (174.2/250 = 69.68%): US 40 (7, includes concurrencies with US 24, US 169, I-35 and US 71), US 40 (77.4), US 40 (89.8)
IL (29.7/155.74 = 19.07%): I-55 (16.1, includes concurrency with US 40), US 40 (5.6), I-57 (6.2), US 40 (1.8)
IN (20.6/156.6 = 13.15%): US 40 (11.2), I-65 (1.5), US 35 (7.9)
OH (29.3/225.6 = 12.99%): US 35 (1.8), OH 49 (1.2), OH 4 (6.3), I-71 (2), US 40 (18)
WV (1.3/14.45 = 9%): US 250 (1.3, includes US 40 concurrency)
PA (92.4/167.92 = 55.03%): I-79 (3.5), I-76 (86), US 30 (0.3), US 522 (2.6)
MD (38/93.62 = 40.59%): US 522 (1), US 40 (8), US 40 (29)

Total: 1247.3/

2151.43 = 57.98% concurrent with another route.

I-465 in IN can't even compete at all. 

[OCGuy81]

For I-75, excluding the hidden designations of FL 93 and GA 401:

FL (0/470.88 mi, 0%): No concurrencies
GA (32.5/355.11 = 9.15%): US 41 (7 mi), GA 540 (16 mi), I-85 (8 mi), GA 5 (1.5 mi)
TN (36.5/161.86 = 22.55%): US 11/US 64 (4 mi), I-40 (17 mi), I-275 (3.5 mi), US 25W (5.7 mi), TN 63 (6.3 mi)
KY (27.3/191.78 = 14.24%): US 25/421 (1.5 mi), I-64 (6.8 mi), I-71 (19 mi)
OH (6.8/211.30 = 3.22%): I-71 (0.5 mi), US 27/52 (1 mi), OH 4 (2 mi), OH 15 (2.1 mi), US 23 (1.2 mi)
MI (85.5/395.54 = 21.62%): US 23 (73.5 mi), M-55 (12 mi)

Total: 188.6/1786.47 = 10.56% concurrent with another route. Much higher compared to its peer x5, I-65 and I-95, mentioned earlier in the thread.

I think the "loser" of this thread for long interstates might be I-25 or I-70. Unlike some other x0, like I-90, I-80 and I-40, I-70 doesn't have a US route truncated because of it, and that it's shorter than those three x0 mentioned, so percentage wise, it's going to be higher.
UT (208.5/232.15 = 89.91%): US 89 (33.5), US 50 (175), with US 6 joining in the middle of the US 50 overlap
CO (261.5/449.59 = 58.16%): US 6/US 50 (11.1), US 6 (18), US 6 (5.3), US 6 (23.2), US 6 (34.3, includes SH 9 concurrency), US 6 (28.1, includes US 40 concurrency), US 40 (2.2), US 6/US 85 (2), US 36 (36.8), US 40/287 (47.1, portion of concurrency counted under US 36), US 24 (42), US 24 (11.4)
KS (391.8/422.82 = 92.66%): US 24 (45.8), US 40 (329.5, includes concurrencies with K-14, K-18, K-4 and US 75), US 24/US 40 (16.5, includes concurrencies with US 69 and US 169)
MO (174.2/250 = 69.68%): US 40 (7, includes concurrencies with US 24, US 169, I-35 and US 71), US 40 (77.4), US 40 (89.8)
IL (29.7/155.74 = 19.07%): I-55 (16.1, includes concurrency with US 40), US 40 (5.6), I-57 (6.2), US 40 (1.8)
IN (20.6/156.6 = 13.15%): US 40 (11.2), I-65 (1.5), US 35 (7.9)
OH (29.3/225.6 = 12.99%): US 35 (1.8), OH 49 (1.2), OH 4 (6.3), I-71 (2), US 40 (18)
WV (1.3/14.45 = 9%): US 250 (1.3, includes US 40 concurrency)
PA (92.4/167.92 = 55.03%): I-79 (3.5), I-76 (86), US 30 (0.3), US 522 (2.6)
MD (38/93.62 = 40.59%): US 522 (1), US 40 (8), US 40 (29)

Total: 1247.3/

2151.43 = 57.98% concurrent with another route.

I-465 in IN can't even compete at all. 

What percentage of its route ISN'T shared? That would be the smaller number.

[SkyPesos]

I think the "loser" of this thread for long interstates might be I-25 or I-70.

I'll try I-25 too
NM (457.6/462.1 = 99.03%): US 85 (457.6). Includes all other concurrencies in the state.
CO (100%): US 87 (299.7). Includes all other concurrencies in the state.
WY (275/301 = 91.36%): US 87 (275). Includes all other concurrencies in the state.

1032.3/1062.8 = 97.13% concurrent 

Here's I-90
WA (65.5/296.92 = 22.06%): US 97 (4.8), US 395 (60.7, includes US 2 concurrency)
ID (0%): No concurrencies
MT (265.5/551.68 = 48.13%): MT 200 (14.1, includes US 93 and part of US 12 concurrencies), US 12 (63.8), I-15 (7.6), US 191 (58, includes US 89 concurrency), US 212 (76.7, includes part of US 87 concurrency), US 85 (45.3)
WY (82.7/208.8 = 39.61%): US 87 (25.4, includes US 14 concurrency), US 87 (12.2), US 14/US 16 (25.3), US 14 (19.8)
SD (154.2/412.76 = 37.36%): US 14 (112, includes various other concurrencies), SD 73 (0.9), SD 63 (7.3), US 83 (20.2), SD 50 (6.8), SD 45 (5.2), SD 37 (1.8)
MN (10.8/275.7 = 3.92%): US 218 (2.8), MN 43 (3), US 14/US 61 (5)
WI (143.6/187.13 = 76.74%): US 53 (1.6), I-94 (92.1, includes part of I-39 concurrency), I-39 (49.9)
IL (33.2/107.13 = 31%): I-39 (17.4), I-94 (15.8)
IN (135.6/156.28 = 86.77%): I-80 (135.6)
OH (169.1/242.91 = 69.61%): I-80 (142), OH 2 (16.1), OH 2 (11)
PA (0%): No concurrencies
NY (0.1/385.48 = 0.03%): I-87 (0.1)
MA (0%): No concurrencies

Total: 1060.3/3020.44 = 35.1% concurrent

Current rankings for x0 and x5s
I-65 (4.17%)
I-95 (7.13%)
I-75 (10.56%)
I-5 (12%)
I-15 (12.7%)
I-90 (35.1%)
I-70 (57.98%)
I-25 (97.13%)

Anyone want to give a try at I-35 and I-55, to round out the "true" x5s?

[TheStranger]

I looked at I-15 as well.  There's a decent amount of concurrencies overall, but all are fairly short.

-NV (21 miles with US-93)
-UT (9 miles with US-50, 10 miles with US-6, 17 miles with US-89, 3 miles with I-80, 38 miles with I-84)
-ID (30 miles with US-91)
-MT (8 miles with I-90, 35 miles with US-287, 11 miles with US-89)

Of the 1,433 miles, there's 182 miles concurrent, or 12.7%

There's also a few concurrencies in California on I-15:

Route 79 for exit 58-61
Route 18 for exit 150-153B

That would increase the total to 187 miles (not too much more) concurrent, bringing I-15 to 13% concurrent.

[OCGuy81]

I think the "loser" of this thread for long interstates might be I-25 or I-70.

I'll try I-25 too
NM (457.6/462.1 = 99.03%): US 85 (457.6). Includes all other concurrencies in the state.
CO (100%): US 87 (299.7). Includes all other concurrencies in the state.
WY (275/301 = 91.36%): US 87 (275). Includes all other concurrencies in the state.

1032.3/1062.8 = 97.13% concurrent 

Current rankings for x0 and x5s
I-65 (4.17%)
I-95 (7.13%)
I-75 (10.56%)
I-5 (12%)
I-15 (12.7%)
I-70 (57.98%)
I-25 (97.13%)

Anyone want to give a try at I-35 and I-55, to round out the "true" x5s?

Anyone want to add I-85 to that list to round out the x5s?

[TheStranger]

Interstate 85:

666.05 miles total

Alabama: 10 miles for US 80, 13 miles for US 29/AL 15 (including 4 miles of US 280/AL 38)
Georgia: 8 miles for I-75/GA 295
South Carolina: 8 miles for US 29
North Carolina: 6 miles for US 29 near Kings Mountain, 17 miles for US 601, 11 miles for US 52 (including US 29 and US 70 in portions), 2 miles of US 29/US 70 near Greensboro, 6 miles for US 421, 32 miles for I-40, then a 16-mile stretch concurrent with portions of US 70, US 15, and US 501.  2 miles for US 158.
Virginia: US 460 for 7 miles


138 miles overlapped, or 20.7%

[OCGuy81]

Interstate 85:

666.05 miles total

Alabama: 10 miles for US 80, 13 miles for US 29/AL 15 (including 4 miles of US 280/AL 38)
Georgia: 8 miles for I-75/GA 295
South Carolina: 8 miles for US 29
North Carolina: 6 miles for US 29 near Kings Mountain, 17 miles for US 601, 11 miles for US 52 (including US 29 and US 70 in portions), 2 miles of US 29/US 70 near Greensboro, 6 miles for US 421, 32 miles for I-40, then a 16-mile stretch concurrent with portions of US 70, US 15, and US 501.  2 miles for US 158.
Virginia: US 460 for 7 miles


138 miles overlapped, or 20.7%

Nicely done! Thank you.

[bassoon1986]

Here's a stab at I-55. Let me know if I've missed any.

LA (28 of 65.81 miles):  US 51 (28 mi)

MS (57.2 of 290.41 miles): US 98 (4.7 mi), US 51 (31.32 mi), MS 16 (6.69 mi), MS 7 (5.32 mi), I-69 (9.17 mi)

TN (6.08 of 12.28 miles): I-69 (5.5), US 61/64/70/79 (0.58)

AR (23.19 of 72.22 miles): US 61/64/70/79 and US 63 overlaps (23.19 mi)

MO (32.02 of 210.45 miles): US 61 (24.92 mi), US 61 and MO 74 overlaps (5.52 mi), I-44 (1.21 mi), I-64 (0.37 mi)

IL (44.9 of 293.8 miles): I-64/US 40/GRR/I-70 overlaps (19.08 mi), I-72 (5.19 mi), Historic US 66 (4.63 mi), I-74/US 51 overlaps (7.93 mi), Historic US 66 (8.07 mi)

Total: 191.39 of 964.25 miles / 19.85%


iPhone

[SkyPesos]

Here’s a stab at I-55. Let me know if I’ve missed any.

LA (28 of 65.81 miles):  US 51 (28 mi)

MS (57.2 of 290.41 miles): US 98 (4.7 mi), US 51 (31.32 mi), MS 16 (6.69 mi), MS 7 (5.32 mi), I-69 (9.17 mi)

TN (6.08 of 12.28 miles): I-69 (5.5), US 61/64/70/79 (0.58)

AR (23.19 of 72.22 miles): US 61/64/70/79 and US 63 overlaps (23.19 mi)

MO (32.02 of 210.45 miles): US 61 (24.92 mi), US 61 and MO 74 overlaps (5.52 mi), I-44 (1.21 mi), I-64 (0.37 mi)

IL (44.9 of 293.8 miles): I-64/US 40/GRR/I-70 overlaps (19.08 mi), I-72 (5.19 mi), Historic US 66 (4.63 mi), I-74/US 51 overlaps (7.93 mi), Historic US 66 (8.07 mi)

Total: 191.39 of 964.25 miles / 19.85%


iPhone

I'll take out the historic US 66 concurrencies and count it as 178.83 miles and 18.55%

Current rankings for x0 and x5s
I-65 (4.17%)
I-95 (7.13%)
I-75 (10.56%)
I-5 (12%)
I-15 (12.7%)
I-55 (18.55%)
I-85 (20.7%)
I-90 (35.1%)
I-70 (57.98%)
I-25 (97.13%)

I may try I-35 next, though how would you count the suffixes? Count both 35W and 35E in? Count 35E only for exit number continuity? Or leave both of them out?

[Dirt Roads]

Not particularly long haul, but I-79 only has 9.4 miles of US-19 in West Virginia and 3.5 miles of I-70 in Pennsylvania.  That's only 3.8% of 338.6 miles total.

[bassoon1986]

Just got I-35:

TX (163.56 of 503.96 miles): US 83 (17.9 mi), I-10 (2.5 mi), I-410 (3.3 mi), US 290 (8.1 mi), US 190 (5.8 mi), US 77 (36.4 mi), US 77 (56.6 mi), US 77 (32.96 mi)

OK (50.41 of 235.96 miles): US 77 (1.11 mi), US 70 (2.47 mi), OK 53 (2.05 mi), OK 9 (1.35 mi), US 77/I-40/US 270/US 62 overlaps (15.98 mi), I-44/OK 66/US 77 overlaps (19.81 mi), US 64 (7.64 mi)

KS (97.16 of 235.53 miles): US 50/US 169 overlaps (95.63 mi), US 69 (1.53 mi)

MO (46.98 of 114.74 miles): I-70/I-29 overlaps (5.59 mi), MO 110 (41.39 mi)

IA (14.2 of 219.23 miles): I-80 (14.2 mi)

MN (13.48 of 259.64 miles): MN 23 (10.98 mi), I-94/I-694/US 10 overlaps (6.68 mi), US 2 (2.5 mi)

Total: 392.47 of 1569.06 / 25.01%

I used overlaps on I-35E in both TX and MN since those continue I-35 mileage.


iPhone

[bassoon1986]

I'm having fun with these so I kept going.

I-20

TX (74.5 of 636.08 miles): TX 349/TX 158 overlaps (11.4 mi), US 87 (4.3 mi), TX 208 (1 mi), US 84 (40.4 mi), FM 880 (1.2 mi), TX 108 (3.1 mi), US 287 (1.5 mi), US 259 (7.1 mi), US 80 (4.5 mi)

LA (7.92 of 189.87 miles): US 71 (1.5 mi), US 371 (2.6 mi), US 80 (3.82 mi)

MS (66.36 of 154.61 miles): US 80 (35.25 mi), US 49/I-55 overlaps (5.8 mi), US 80/I-59 overlaps (25.31 mi)

AL (136.95 of 214.7 miles): I-59 (130.3 mi), US 78 (2.83 mi), US 431 (3.82 mi)

GA (14.05 of 202.61 miles): US 278 (14.05 mi)

SC (0 of 141.51 miles)

Total: 299.78 of 1539.4 miles / 19.47%


iPhone

[SkyPesos]

I-80:

CA (19.6/205.07): I-580 (4.8), CA 12 (4.4), CA 113 (4.5), CA 193 (3.5, includes CA 49 concurrency), CA 89 (2.4)
NV (185.7/410.68): Alt US 95 (34.4), US 95 (93.4), US 93 (57.9)
UT (52.7/196.35): I-15 (3), US 189 (49.7)
WY (260/402.78): US 189 (18.3), US 30 (169.2, includes US 191 and US 287 concurrencies), US 30 (41.4), US 30 (31.1)
NE (14.8/455.31): NE 71 (2), NE 10 (4.3), US 77 (8.5)
IA (123.8/306.29): I-29 (3.1), US 6 (4.7), US 6 (49.5), I-35 (14.3), US 65 (1.4), US 6 (22.2), IA 38 (4.1), US 6 (19), US 61 (5.5)
IL (15.1/163.41): IL 110 (6.6), I-294 (5.5), I-94 (3)
IN (151.56 = 100%): I-94, I-90. Not bothering with distances for this one.
OH (147.2/237.48): I-90 (142.8), OH 11 (4.4)
PA (28.5/311.07): PA 66 (4.4), Alt US 220 (2.8), US 220 (17.3), US 209 (4)
NJ (2/68.54): US 206 (2)

Total: 1000.96/2899.59 = 34.52% concurrent

Current rankings for x0 and x5s
I-65 (4.17%)
I-95 (7.13%)
I-75 (10.56%)
I-5 (12%)
I-15 (12.7%)
I-55 (18.55%)
I-20 (19.47%)
I-85 (20.7%)
I-35 (25.01%)
I-80 (34.52%)
I-90 (35.1%)
I-70 (57.98%)
I-25 (97.13%)

[MCRoads]

I don't know how to find lengths of concurrencies with just panning over the entire highway on google earth, but I think I-40 might have a relatively low percentage of concurrencies. But, this might be cheating a bit, since the interstate followed US 66 for most of its length past Oklahoma City.

[Crown Victoria]

I-10:


CA: SR 1 (0.96), I-5 (2.77), US 95 (3.32) Total: 7.05/243.31
AZ: US 95 (17.54), US 60 (5.68), US 191 (20.78) Total: 44/391.99
NM: Combination of US 70, US 180, and US 85 concurrencies, Total: 139.7/164.26
TX: US 180 (24), SH 17 (2.5), US 67 (24.5), US 83 (9.1), US 87 (54.1, includes briefly I-35), US 90 (114.6, not including part counted with US 87, multiple sections), SH 130 (10.9 separate from US 90), SH 71 (1.8), US 69/US 96/US 287 (1.5 separate from US 90) Total: 243/879.6
LA: US 90 (9.8) Total: 9.8/273.6
MS: 0/77
AL: 0/66.27
FL: US 17 (1.01) Total: 1.01/362.06

Grand Total: 444.56/2460.34=18.07% concurrent

[SkyPesos]

I don't know how to find lengths of concurrencies with just panning over the entire highway on google earth, but I think I-40 might have a relatively low percentage of concurrencies. But, this might be cheating a bit, since the interstate followed US 66 for most of its length past Oklahoma City.

There's a much easier way to find concurrencies without using a map. Go on Wikipedia's page for an interstate highway segment in a state, and scroll down to the exit list table. All the concurrency start and endpoints are highlighted in green.