Parallel - Not Duplexed

[Grzrd]

Years ago, to the southwest of Atlanta's Hartsfield (today known as Hartsfield-Jackson) Airport, I-85 and I-285 were duplexed for a short stretch between the interchange where I-85 was routed to the inside of I-285 and the interchange where I-85 was routed to the outside of I-285.  Later, the two intersections were combined, for lack of a better phrase, into a large "mega-interchange" in which the duplex was eliminated and I-85 and I-285 maintain independent routings.

Two questions:

(1) What is the longest parallel, non-duplexed routing of two interstates in the interstate system (same question for freeways, too)?

(2) I referred to it as a "mega-interchange"; should the system in the link above properly be considered as one interchange or two interchanges?

[NE2]

Highway 401 Collectors and Highway 401 Express

[Ian]

I-295 and the New Jersey Turnpike run parallel for quite a distance between the Delaware Memorial Bridge and up to Trenton.

[Kacie Jane]

I-295 and the New Jersey Turnpike run parallel for quite a distance between the Delaware Memorial Bridge and up to Trenton.

That's not the sort of parallel routes he's talking about though.  He's talking about specifically where one freeway is sort of "inside" another -- the way the Garden State Parkway and US 9 are between Exits 127 and 129, or I-295 and I-76 where the latter ends and turns into NJ 42.

Or, as NE2 cheekily pointed out, similar to any local/express setup, or the NJTP's truck and car lanes... except with two different freeways involved.

[xonhulu]

Years ago, to the southwest of Atlanta's Hartsfield (today known as Hartsfield-Jackson) Airport, I-85 and I-285 were duplexed for a short stretch between the interchange where I-85 was routed to the inside of I-285 and the interchange where I-85 was routed to the outside of I-285.  Later, the two intersections were combined, for lack of a better phrase, into . . . a large "mega-interchange" in which the duplex was eliminated and I-85 and I-285 maintain independent routings.

Two questions:

(1) What is the longest parallel, non-duplexed routing of two interstates in the interstate system (same question for freeways, too)?

(2) I referred to it as a "mega-interchange"; should the system in the link above properly be considered as one interchange or two interchanges?

Isn't there a similar situation with I-90 and I-790 in Utica, NY?  A little different in that I-790 ends in the interchange while I-85 & I-285 intersect and continue, but I-90 is "inside" of I-790 for some distance.

[PurdueBill]

Had they built the I-271/I-480 duplex the way they could have, using what to this day is a wide median with ghost grading for lanes like the express lanes to the north on 271 (with overpasses that are there designed and built to accommodate those lanes too), 480 could have come and go on the outer lanes while 271 would have continued along on the inner lanes.  (Instead, 2 lanes of each merge to form 3, and then the 3 split a couple miles later to 2+2--so staying on a route doesn't involve changing lanes but the roadways do combine.  Close but not quite....)

[roadman65]

I-80 and NJ 17 in Hasbrouck Heights, NJ where the interstate is inside NJ 17.
US 92 and I-4 near Tampa where US 92 is outside of I-4 at the interchange with US 301.
US 22 and Garden State Parkway in Union, NJ.
FL 15 and FL 408 in Orlando where FL 15 is the two service roads from Mills Avenue to Crystal Lake Drive.
FL 426 and I-4 in Downtown Orlando for one block from Robinson to Washington Streets.

[kurumi]

CT 15 parallels I-91 in Meriden (south of I-691) and in Hartford (south of the Charter Oak Bridge). Meriden has I-91 inside the CT 15 lanes, and Hartford has each freeway side by side.

[Takumi]

Something like that occurs with I-73 and I-85 on the Greensboro Urban Loop.

[roadman65]

What about US 301 at I-95 North of Richmond, VA where US 301 is outside of I-95 through the interchange?

[Ian]

I-295 and the New Jersey Turnpike run parallel for quite a distance between the Delaware Memorial Bridge and up to Trenton.

That's not the sort of parallel routes he's talking about though.  He's talking about specifically where one freeway is sort of "inside" another -- the way the Garden State Parkway and US 9 are between Exits 127 and 129, or I-295 and I-76 where the latter ends and turns into NJ 42.

Or, as NE2 cheekily pointed out, similar to any local/express setup, or the NJTP's truck and car lanes... except with two different freeways involved.

*D'oh* I see now.

[hbelkins]

How about I-85 and US 74 near Kings Mountain, NC?

http://g.co/maps/sgecx

[roadman65]

How about I-85 and US 74 near Kings Mountain, NC?

http://g.co/maps/sgecx

Looks like a winner.

[national highway 1]

I-205 & I-84/US 30 in Portland OR.

[Takumi]

What about US 301 at I-95 North of Richmond, VA where US 301 is outside of I-95 through the interchange?

Close, but 301 isn't a freeway there.

[xonhulu]

I-205 & I-84/US 30 in Portland OR.

I thought of this, too, but the freeways are side-by-side, not one inside the other like the example in the OP.

[agentsteel53]

I-355 in Illy runs parallel with a free road whose number I cannot remember for the life of me

[Bickendan]

I-35W and I-94, Minneapolis

As for the longest one: AP-7 and B-30 in Barcelona, 6.5 miles long. http://cmap.m-plex.com/hb/hwymap.php?mt=g&r=esp.b030&sys=espa&rg=all&gr=p&off=100

[national highway 1]

The carriageways of Route 8 are in between the carriageways of Route 3 for about 2km, in Hong Kong.
http://g.co/maps/9hf2a

[TheStranger]

Technically "unbuilt" but had the I-80 realignment from Foothill Farms to midtown Sacramento been completed (instead of its cancellation leading to the old I-80/US 99E/US 40 becoming Business 80 in 1982), the new alignment would have run within the lanes of what is today's I-80 from exits 93 to 95, but what was originally I-880:

http://maps.google.com/maps?q=Foothill+Farms,+CA&hl=en&ll=38.643758,-121.391716&spn=0.037206,0.055189&sll=35.246145,-81.304021&sspn=0.019452,0.027595&vpsrc=6&hnear=Foothill+Farms,+Sacramento,+California&t=h&z=14

[Brandon]

I-355 in Illy runs parallel with a free road whose number I cannot remember for the life of me

I-355 and I-88, as well as I-290 and I-294.

[NE2]

SR 91 and 91 Express Lanes. The latter are technically a separate freeway.

[jwolfer]

Years ago, to the southwest of Atlanta's Hartsfield (today known as Hartsfield-Jackson) Airport, I-85 and I-285 were duplexed for a short stretch between the interchange where I-85 was routed to the inside of I-285 and the interchange where I-85 was routed to the outside of I-285.  Later, the two intersections were combined, for lack of a better phrase, into a large "mega-interchange" in which the duplex was eliminated and I-85 and I-285 maintain independent routings.

Two questions:

(1) What is the longest parallel, non-duplexed routing of two interstates in the interstate system (same question for freeways, too)?

(2) I referred to it as a "mega-interchange"; should the system in the link above properly be considered as one interchange or two interchanges?

I-95 and FL Turnpike in Southern Martin County are literally right next to one another for a few miles. 

[pianocello]

I-696 and the Lodge NW of Detroit: 1.6 miles
I-88 and I-355: 1.3 miles

[MrDisco99]

In the Bronx, the Cross Bronx Expressway straddles the Bruckner Expressway for about half a mile or so where I-95 transitions from one to the other and I-278 and I-295 begin and end.  I think this is considered one huge interchange, though.