Most populous area bounded by Interstates

[hotdogPi]

(Interstates only. If you can reach the ocean, Canada, or Mexico, it doesn't count.)

Contenders I can think of:

1. The region that includes Fresno. It also has some of the Inland Empire and the Las Vegas and Salt Lake City metro area.

2. The Texas Triangle, which includes a decent amount of Austin and a few suburbs of San Antonio and Houston.

3. The region that includes Yonkers and a whole bunch of other NYC suburbs.

https://sedac.ciesin.columbia.edu/mapping/popest/gpw-v4/ might be helpful.

[webny99]

Can we "skip over" interstates?

For example, could I use I-86/I-81/I-90, or is that disqualified because I-390 runs through the middle of that area?

[hotdogPi]

Can we "skip over" interstates?

For example, could I use I-86/I-81/I-90, or is that disqualified because I-390 runs through the middle of that area?

It would be two separate areas, as I-390 runs through the middle.

If an Interstate dead ends in the middle of a region, like I-27, you can ignore it. Imagine using the fill command in MS Paint, AutoCAD, or similar.

[GaryV]

What about inside the beltway in Washington DC?  You get most of DC (excluding the part south of I-695), a lot of MD suburbs and VA suburbs north of I-66.

EDIT: Since I-66 dead ends (see the I-27 example in the OP), you can add all the VA suburbs north of I-395 as well.

Unlike most cities, Washington doesn't have an Interstate that goes through the city.

[CNGL-Leudimin]

(Interstates only. If you can reach the ocean, Canada, or Mexico, it doesn't count.)

Dang, because it's precisely the area outside the Interstates the most populous one . Well over 90% of the people live there.

[AlexandriaVA]

What about inside the beltway in Washington DC?  You get most of DC (excluding the part south of I-695), a lot of MD suburbs and VA suburbs north of I-66.

EDIT: Since I-66 dead ends (see the I-27 example in the OP), you can add all the VA suburbs north of I-395 as well.

Unlike most cities, Washington doesn't have an Interstate that goes through the city.

It comes down to if 395 (14th St Bridge) 695 (11th St Bridge) 295 are actually all continuous. I don't know where DC-295 and I-295 actually "hand off" in Anacostia. If they hand off at the 11th St bridge intersection, then you have to omit much of Alexandria, SW DC and some of SE DC near Bolling AFB. If not, then all of inside the Beltway is counted.

https://www.google.com/maps/@38.8661896,-76.991394,3a,75y,31.99h,89.7t/data=!3m6!1e1!3m4!1sy3RGbfI-LWAfy82vPFwyQw!2e0!7i16384!8i8192

I think it's close enough that 395-695-295-495 should be considered a closed loop.

[Max Rockatansky]

Regarding Fresno and was part of Southern California I believe that probably would be the winner.  That boundary essentially is; I-5, I-80, I-215, I-15, and I-210.  Some of the large population centers within that boundary would be:

-  The outskirts of Los Angeles. 
-  Santa Clarita
-  Bakersfield
-  Visalia
-  Fresno
-  Modesto
-  Stockton
-  Reno
-  Salt Lake City
-  St. George
-  Las Vegas
-  Parts of the Inland Empire like San Bernardino and Fontana.

[DTComposer]

1. The region that includes Fresno. It also has some of the Inland Empire and the Las Vegas and Salt Lake City metro area.
https://sedac.ciesin.columbia.edu/mapping/popest/gpw-v4/ might be helpful.

Rough approximation, using:
5 - 80 - 215 (UT) - 15 - 10 - 605 - 210 (CA) - 5: about 10,750,000

It also includes the majority of the Sacramento metro.

[sprjus4]

What about inside the beltway in Washington DC?  You get most of DC (excluding the part south of I-695), a lot of MD suburbs and VA suburbs north of I-66.

EDIT: Since I-66 dead ends (see the I-27 example in the OP), you can add all the VA suburbs north of I-395 as well.

Unlike most cities, Washington doesn't have an Interstate that goes through the city.

It comes down to if 395 (14th St Bridge) 695 (11th St Bridge) 295 are actually all continuous. I don't know where DC-295 and I-295 actually "hand off" in Anacostia. If they hand off at the 11th St bridge intersection, then you have to omit much of Alexandria, SW DC and some of SE DC near Bolling AFB. If not, then all of inside the Beltway is counted.

https://www.google.com/maps/@38.8661896,-76.991394,3a,75y,31.99h,89.7t/data=!3m6!1e1!3m4!1sy3RGbfI-LWAfy82vPFwyQw!2e0!7i16384!8i8192

I think it's close enough that 395-695-295-495 should be considered a closed loop.

I-295 ends at I-695.

[debragga]

There's a big chunk of Texas/Oklahoma/Arkansas that could qualify, it includes a good bit of the suburbs north of Dallas.

Going clockwise from DFW:

I-635
I-35E/I-35
I-240
I-40
I-430
I-30

I-540 and parts of the unfinished I-49 are in this area, but neither of those bisect it.

[Eth]

Contenders I can think of:

2. The Texas Triangle, which includes a decent amount of Austin and a few suburbs of San Antonio and Houston.

https://sedac.ciesin.columbia.edu/mapping/popest/gpw-v4/ might be helpful.

Using I-20, I-45, I-610, I-10, I-410, I-35, and I-35E, this is about 3.7 million.

About the same (3.7 million) is the wedge in GA/TN/NC/SC using I-75, I-40, I-26, I-85, and I-285.

[kphoger]

Can we "skip over" interstates?

For example, could I use I-86/I-81/I-90, or is that disqualified because I-390 runs through the middle of that area?

It would be two separate areas, as I-390 runs through the middle.

If an Interstate dead ends in the middle of a region, like I-27, you can ignore it. Imagine using the fill command in MS Paint, AutoCAD, or similar.

Oh, so I should stop drawing this boundary?

[webny99]

It would be two separate areas, as I-390 runs through the middle.

If an Interstate dead ends in the middle of a region, like I-27, you can ignore it. Imagine using the fill command in MS Paint, AutoCAD, or similar.

Oh, so I should stop drawing this boundary?

Well, you might as well keep going for fun, but it won't win the thread. 

[hobsini2]

Well for the Midwest, I think it would be I-70, I-270, I-55, I-155, I-74, I-80, I-280, I-80, I-235, I-35, I-435. You would have parts of the suburbs of St Louis, Springfield, Peoria, Quad Cities, Iowa City, Des Moines, the suburbs of Kansas City, and Columbia. Using the counties the loop is in plus the inside of the loop.

I-70/I-270 MO Corridor: 2,361,156
Jackson, Lafayette, Saline, Cooper, Boone, Calloway, Montgomery, Warren, St Charles, St Louis Co.
I-435/I-35 MO Corridor: 282,388
Clay, Clinton, Caldwell, DeKalb, Daviess, Harrison
I-35/I-235 IA Corridor: 494,608
Decatur, Clarke, Warren, Polk
I-80/I-280 IA Corridor: 386,716
Jasper, Poweshiek, Iowa, Johnson, Cedar, Scott
I-280/I-74 IL Corridor: 572,839
Rock Island, Henry, Knox, Peoria, Tazewell
I-155/I-55/I-270 IL Corridor: 574,921
Logan, Sangamon, Montgomery, Macoupin, Madison
Inside MO: 352,573
Ray, Mercer, Grundy, Livingston, Carroll, Putnam, Sullivan, Linn, Chariton, Howard, Randolph, Macon, Adair, Schuyler, Scotland, Clark, Knox, Lewis, Shelby, Marion, Monroe, Ralls, Audrain, Pike, Lincoln
Inside IA: 343,765
Wayne, Lucas, Marion, Mahaska, Keokuk, Washington, Louisa, Muscatine, Des Moines, Henry, Lee, Van Buren, Jefferson, Wapello, Davis, Appanoose, Monroe
Inside IL: 344,602
Jersey, Calhoun, Greene, Pike, Scott, Menard, Mason, Morgan, Cass, Brown, Adams, Hancock, Henderson, McDonough, Fulton, Mercer, Warren

MO Total: 2,996,117
IA Total: 1,225,089
IL Total: 1,492,362
Grand Total: 5,713,568

[RobbieL2415]

The triangle in Throgs Neck, Bronx, comes to mind.

[STLmapboy]

What about TX-99 in Houston? If completed (and it probably won't anytime soon) it would be the largest loop freeway in the US. What's the current largest?

[sprjus4]

What about TX-99 in Houston? If completed (and it probably won't anytime soon) it would be the largest loop freeway in the US. What's the current largest?

Most populous area bounded by Interstates

Either way, other interstates inside of TX-99 create smaller areas.

[Roadgeekteen]

Probably I-95/I-93/South of I-90 for Massachusetts.

[3467]

I live within that boundary Hobsini . Since  72 is a spur of doesn't count right?
All that area and we add up to Cook County.

[corco]

The area bounded by I-10, 17, 40, and 25 is probably pretty large - that's more than half of Phoenix metro, most of Tucson, most of Las Cruces, and part of Albuquerque - though admittedly there's a whole lot of nothing in the middle. The NASA tool estimates it at 4.1 million.

I'd assume the Central Valley polygon wins though.

[pianocello]

Well for the Midwest, I think it would be I-70, I-270, I-55, I-155, I-74, I-80, I-280, I-80, I-235, I-35, I-435. You would have parts of the suburbs of St Louis, Springfield, Peoria, Quad Cities, Iowa City, Des Moines, the suburbs of Kansas City, and Columbia. Using the counties the loop is in plus the inside of the loop.

Gotta be careful about that, though. Many of the counties that these Interstate corridors pass through have most of their population on the other side of the highway. Off the top of my head, I know that's true for Polk, Jasper, and Scott in Iowa; Rock Island, Peoria, and Tazewell (although that's probably more of an even split) in Illinois; and St. Louis and St. Charles in Missouri. Just from the 3 Iowa counties, I bet that's probably about half of your population estimate for the state.

On the other hand, I can't think of another Interstate polygon in the Midwest that would contain more people. Maybe I-43/90/294/94, but that only contains fractions of the Chicago and Milwaukee metro areas.