Longest distance you can travel on just 3dis

[kirbykart]

Rules:
1: No backtracking/looping back around to a previously traveled segment of the 3di.
2: You are allowed to cross state lines.
3: Concurrencies with 2dis are allowed as long as you only use the portion of the 2di that is actually concurrent with the 3di.
4: Let the fun begin!

[MATraveler128]

132 miles on I-476 from I-95 in Chester to I-81 in Scranton.

[TheHighwayMan3561]

164 on I-495 (MA) and I-195 (MA/RI)

[US 89]

194 miles via I-195 (RI/MA), I-495 (MA), I-290 (MA), and I-395 (MA/CT).

[GaryA]

SF Bay Area:  I-280 to I-880 to I-980 to I-580 to I-680, 165 or so miles.  As a bonus, you'll pass by I-380 and I-780 (and both ends of I-238).

[7/8]

About 124 miles in LA (using I-405, 110, 105, 710, 405, 605, and 210).

[kirbykart]

142 miles on I-495 from north end, down to Worcester, then take 290 at Worcester. Use 290 and 395 to the latter's southern terminus.

[kirbykart]

About 124 miles in LA (using I-405, 110, 105, 710, 405, 605, and 210).

It may not be the longest, but in the sheer number of 3dis that route uses, it's a winner.

[BrianP]

This ones theoretical ATM.  But it should be doable in the future, ~240 miles: DE 495, DE/NJ/PA 295, PA 276, PA 476. 

But the PA turnpike interchange with I-295 isn't complete yet.

[SEWIGuy]

SF Bay Area:  I-280 to I-880 to I-980 to I-580 to I-680, 165 or so miles.  As a bonus, you'll pass by I-380 and I-780 (and both ends of I-238).

I have a longer one in the Bay Area.  From I-80:  I-680, I-280, I-880, I-580.  About 175 miles.

[Scott5114]

Doing I-470 in MO, then I-435 and looping back around to the I-470 junction gets you just about 100 miles exactly.

[kirbykart]

Doing I-470 in MO, then I-435 and looping back around to the I-470 junction gets you just about 100 miles exactly.

Good example involving a beltway.

[SkyPesos]

Few more involving beltways:

- I-270 SB entire route, then loop around I-495 clockwise back to I-270 junction: about 100 miles
- I-471 SB entire route, then loop around I-275 back to I-471 junction (either direction): about 90 miles.

[webny99]

194 miles via I-195 (RI/MA), I-495 (MA), I-290 (MA), and I-395 (MA/CT).

Darn it, I had that one all mapped out before reading the thread, only to come back and see it was already mentioned. 

[webny99]

Too bad there's no access between I-295 and I-276 northeast of Philly, or you'd have:

I-495 > I-295 (103 miles) + I-276 > I-476 (133 miles) for a total of 236 miles.

[webny99]

I-390 NB > I-590 NB > I-490 WB to end = 101 miles
I-278 EB > I-295 SB > I-495 EB to end = 102 miles

And this one's a little questionable because of the ramp configuration, but if I-287 to I-684 counts as continuous, it's 122 miles from I-287's southern terminus to I-684's northern terminus.

[Scott5114]

Another Kansas example: Start in Salina and head south on I-135 to exit 1C in Wichita. Then take I-235 to loop back north until you intersect with I-135 again. This is 111 miles.

[ilpt4u]

Few more involving beltways:

- I-270 SB entire route, then loop around I-495 clockwise back to I-270 junction: about 100 miles

Technically, starting with 270 SB, and then going clockwise around the Beltway, you can measure up to the 270/270 Spur split for the end point

I do wonder, tho, is this mileage greater than 270 SB, around 495 Counterclockwise, and then using (unsigned) 595 to its official endpoint in Annapolis, wherever exactly that is?

[jp the roadgeek]

I-390 NB > I-590 NB > I-490 WB to end = 101 miles
I-278 EB > I-295 SB > I-495 EB to end = 102 miles

And this one's a little questionable because of the ramp configuration, but if I-287 to I-684 counts as continuous, it's 122 miles from I-287's southern terminus to I-684's northern terminus.

Imagine if I-287 were extended to I-278 via NJ/NY 440, then you could have a 234 mile loop from Riverhead to Brewster of I-495 W > I 295 N > I 278 W > I-287 N/S > I 684 N, assuming a concurrency of a 3di with its parent is allowed.

[Flint1979]

In Michigan it'd just be the 81 miles of I-196, none of the 3di's in Michigan connect with each other so you'd could only do this using one Interstate.

[cwf1701]

In Michigan it'd just be the 81 miles of I-196, none of the 3di's in Michigan connect with each other so you'd could only do this using one Interstate.

You forgot that I-275 and I-696 meet northwest of Detroit. starting at I-94 and 11 Mile, you could take I-696 for 29 miles, then take I-275 south for 38 miles, the combination of I-696 and I-275 is almost 67 miles.

[vdeane]

I-390 NB > I-590 NB > I-490 WB to end = 101 miles
I-278 EB > I-295 SB > I-495 EB to end = 102 miles

And this one's a little questionable because of the ramp configuration, but if I-287 to I-684 counts as continuous, it's 122 miles from I-287's southern terminus to I-684's northern terminus.

Google is incorrect, those "ramps" are actually the I-684 mainline, so it counts.  What Google has as I-684 is actually a reference route.

[kirbykart]

I-390 NB > I-590 NB > I-490 WB to end = 101 miles

That was actually my very first idea for this, but I didn't get to posting it. I actually can't believe that's a full 100 miles!

[kirbykart]

assuming a concurrency of a 3di with its parent is allowed.

I think I will allow this. I'll add it to the original post.

[Road Hog]

Theoretically if the 3di involved is a complete beltway, the answer is "infinity."