Parallel - Not Duplexed

[Alps]

NJ 124 is the frontage roads of NJ 24 for over 2 miles, although 124 isn't a freeway.

[akotchi]

NJ 124 is the frontage roads of NJ 24 for over 2 miles, although 124 isn't a freeway.

Along those same lines, S.R. 84 forms the frontage roads for I-595 in South Florida, for about 10 or so miles (?).  S.R. 84 is not a freeway in this case, either.

[Duke87]

Dulles Toll Road (VA 267) and Dulles Access Road (unsigned VA 90004). The latter is entirely within the former for 10 miles.

[Stratuscaster]

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

As Brandon noted - it's not a free road - it's I-88 Toll.

Going N-S, IL 53 runs parallel to I-355 for a good distance - but I don't think that counts here.

[bassoon1986]

I-45 and I-10 downtown Houston

[achilles765]

And in addition to IH 45 and IH 10, also Us 59 and TX 288 heading south of downtown form a parallel routing that is a good 16 lanes across.  59 forms the outer lanes and 288 is on the inside, with the northbound side of 288 basically forming the ramps to IH 45 from BOTH highways

[vtk]

The first half mile or so of I-71 is inside I-64 in Louisville.

A bit of the Central Florida Greenway straddles I-4 near Orlando.

There are outer roadways on I-270 and OH 161 in northeastern Columbus that could be considered a continuous (unnumbered) freeway, with never less than 2 lanes each direction.

[dislocatedkid]

The brand new "crosstown commons" interchange between i-35w & mn-62 south of Minneapolis employs this tactic.

[roadman65]

How about FL 618 in Tampa, Florida with its reversable express lanes in the median of the main freeway?  Its not only like I-395 in Virginia, but elevated and a totally seperate highway as its endpoints are different from FL 618's terminuses.  The express Freeway goes from local streets in Brandon to Downtown Tampa with slip ramps between the main freeway and it.  You MUST have SUNPASS to use it during its lane operations as it has NO TOLLBOOTHS on it at all.  Nonetheless, they use the same alignement for miles.

[Grzrd]

I have come to detest the terms "duplex" and "multiplex"

"Overlap" is also better than "multiplex," but I dunno, somehow it doesn't seem like the most appropriate term to me.  "Concurrency" still works best for me.  However, if state DOT's prefer overlap, I'd rather use the term that's most official.  

Depends on the DOT. Some do use concurrency. Personally I find that a bit stilted, but that's just me.

(above quotes from ""Exit" on Two 2di Duplex" thread)

I agree with NE2, xonhulu and HB that using an official term is preferable.  I used the "d-word" in the title of this thread and the above-quoted thread because I have seen it used at roadgeek sites over the years; like HB, I've never really liked the term, either - just tried to speak the local language.

This thread has established that there are multiple instances of two independent routes converging to the point where one route has its carriageways inside of the carriageways of the other route, with each route maintaining independent signage and mileage markers.  Is there a specific official (DOT, engineering, whatever) term for this type of alignment?  Until one is uncovered, is the phrase "parallel routing overlap" adequate?  Lends itself to a good acronym: "PRO"    

[Hot Rod Hootenanny]

There are outer roadways on I-270 and OH 161 in northeastern Columbus that could be considered a continuous (unnumbered) freeway, with never less than 2 lanes each direction.

No different than the "double freeway" ODOT built for I-270 between US 40/Main St and I-70 on the east side.

[vtk]

There are outer roadways on I-270 and OH 161 in northeastern Columbus that could be considered a continuous (unnumbered) freeway, with never less than 2 lanes each direction.

No different than the "double freeway" ODOT built for I-270 between US 40/Main St and I-70 on the east side.

You missed the scope of my example.  One continuous unnumbered freeway from south of Easton Way to Little Turtle Way.  It has I-270 in its median for a few miles, and OH 161 in its median for another mile or so.  Arguably, it's not just the local lanes of either numbered highway.