What kind of interchange is this?

[bugo]

It's at I-40 and I-44 in Oklahoma City. It functions as a complete freeway to freeway interchange but it has left entrances and exits. It was obviously built on the cheap so you could call it a "ghetto interchange" or a "welfare stack". At least it isn't a cloverleaf.

Nexus 5X

[jakeroot]

"Directional" interchange; alternatively, "Fully Directional". Stacks are technically fully directional, but for some reason get their own name.

[dfilpus]

In Detroit MI, the Lodge (M-10) / Ford (I-94) interchange is also a fully directional interchange.

https://goo.gl/maps/1B3roXaXDsS2

[ilpt4u]

"Directional" interchange; alternatively, "Fully Directional". Stacks are technically fully directional, but for some reason get their own name.

Is the difference with these vs a Stack Interchange, the presence of Left Exits/Entrances?

Makes me think of the I-80/I-57 Interchange, tho that one has a couple of Loop Ramp movements
https://www.google.com/maps/@41.5658891,-87.7410769,959m/data=!3m1!1e3

[kurumi]

I read a few DOT interchange docs and found 2 uses of "semi-directional":

• semi-directional ramp may diverge from the final direction of travel, but not form a loop. IOW, a standard stack has semi-directional ramps. A 3-way interchange with "left exits" (US) has directional ramps.
• semi-directional interchange: minor left turns are handled with cloverleaf loops, but the higher-traffic left turns are handled with directional or semi-directional ramps. Here, a stack would be fully directional (no loops), and a "cloverstack" would be semi-directional.

See also:
https://www.in.gov/dot/div/contracts/standards/dm-Archived/10Metric/Part5/Ch48/DCh48.pdf (pg 26)
https://wsdot.wa.gov/publications/manuals/fulltext/M22-01/1360.pdf (pg 2, 4)
https://www1.maine.gov/mdot/hdg/docs/chpt9.pdf (pg 9-7)
https://www.mdt.mt.gov/other/webdata/external/traffic/manual/chapter_29.pdf (pg 22)

[jakeroot]

Ahh, I see. Yep, fully directional, apparently, just means going left to go left, or going right to go right. Whereas a stack has all the ramps on the right (ergo, semi-directional).

I doubt any agency would ever consider building another fully-directional interchange.

[mrcmc888]

Ahh, I see. Yep, fully directional, apparently, just means going left to go left, or going right to go right. Whereas a stack has all the ramps on the right (ergo, semi-directional).

I doubt any agency would ever consider building another fully-directional interchange.

It doesn't surprise me that Oklahoma is the only state where this type of interchange has been found.  Their DOT's ability to fail at even the most basic of highway design is something to be marveled at (but hopefully not to attempt to beat).

[NE2]

In Detroit MI, the Lodge (M-10) / Ford (I-94) interchange is also a fully directional interchange.

https://goo.gl/maps/1B3roXaXDsS2

It doesn't surprise me that Oklahoma is the only state where this type of interchange has been found.  Their DOT's ability to fail at even the most basic of highway design is something to be marveled at (but hopefully not to attempt to beat).

[sparker]

OK -- it does feature LH exits and entrances, currently frowned upon.  But at least it does have lanes dedicated to those exits as well as entrances; there's no immediate merging from the left onto a through lane -- and the radius of the LH-movement curves seems large enough to sustain speeds in at least the '50's.  I've used this interchange on several occasions, including movements from I-40 to both directions of I-44, and experienced no issues with diverging or merging (although I will grant that folks inured to last-minute moves may find it a bit harrowing!).  My only issue with the interchange as it stands would be the fact that there are only 2 through lanes in any direction, with the outside approach lanes dedicated to RH or LH directional changes; expanding the interchange if necessary will be exceptionally difficult.  Of course, nothing like this will likely ever be designed again; the semi-directional "stack" seems to be the better bet (and it's upgradeable regarding through-route capacity).  Now -- from the GSV of the interchange, it could use a paving job, particularly along I-40 (it was a washboard the last time I came through circa 2007, and it looks to be worse now!).  A bit of a disclaimer -- I haven't driven it in peak traffic hours (I've always tended to try to hit OKC during midday).  But I've found it to be at least functional if not especially elegant.   

[jakeroot]

Certainly, it's much better than a damn cloverleaf. But given the ROW requirements, plus the cost, a stack is definitely a better bet.

Anyone know if the MUTCD FHWA frowns upon left exits?

[Brandon]

Wisconsin used to have several of these around Milwaukee.  WisDOT has been getting rid of them recently in favor of semi-directional stacks.

[WR of USA]

In Connecticut, Waterbury's mixmaster interchange appears to be fully directional just with a double leveled highway. If the state ever got their act together, it could be on the list for major replacement.

[SSOWorld]

Wisconsin used to have several of these around Milwaukee.  WisDOT has been getting rid of them recently in favor of semi-directional stacks.

Had been.  The Hale and the Stadium won't be touched - much less the Badger near Madison, the Beltline will be keeping its left exits from SB to WB and EB to NB despite a reconstruction.

[US 89]

Wikipedia calls it a "full diamond" . In fact, that I-40/44 interchange is cited as an example, along with I-94/M-10 in Detroit.

[webny99]

Does this count? (I-490/I-390/NY 390)
One thing I can say for sure is that the above has a lot better spacing, especially between exits than the example in the OP. That creates a larger footprint, but also makes it kind of visually appealing, whereas I-40/I-44 is just outright ugly.

This interchange is actually under construction at the moment - it's going to look like this when complete. I'm pretty sure it will no longer qualify then, but until 2022, it is definitely a candidate for this thread.

It doesn't surprise me that Oklahoma is the only state where this type of interchange has been found.

Not the case at all, as NE2 pointed out. I actually used to think the above example - in my home state of NY - was one-of-a-kind, but learned of various other examples some time ago.

[froggie]

Anyone know if the MUTCD frowns upon left exits?

Doesn't really matter for the MUTCD...this is a design issue, not a signage/wayfinding one.

It's the FHWA that frowns upon left exits...citing reams of research that indicate they're more dangerous and more confusing for motorists.

[jakeroot]

Anyone know if the MUTCD frowns upon left exits?

Doesn't really matter for the MUTCD...this is a design issue, not a signage/wayfinding one.

It's the FHWA that frowns upon left exits...citing reams of research that indicate they're more dangerous and more confusing for motorists.

That's what I meant. My bad.

Even if they were just as understood for motorists, I don't like the idea of passing lanes on freeways, especially in rural areas, having to deal with merging traffic, which could include anything from drivers going well over the limit, who will not cause you an issue, to large trucks possibly merging in at 10-20 below.

Of course, that's all in addition to the whole weaving thing (the dangerous part). In Seattle, we have two famous weaves: the 520 Shuffle (northbound I-5), and the Mercer Weave (southbound I-5). Southbound, you have to change lanes four times in .6 miles; northbound: at least two lane changes in .7 miles (not as bad). That stretch of freeway, from Mercer to 520, is perpetually busy as a result of these weaves.

Left exits are really good, as long as they're exclusively for diamond lane users. Texas-T's having been popping up around Seattle for the last twenty years. Now, we're finally building some freeway-to-freeway diamond lane ramps. Anything to reduce weaving, a serious issue in all metro areas with lots of HOV lanes (here, Minneapolis, LA, San Francisco, Atlanta (I think)).

[briantroutman]

The full freeway-freeway interchange depicted in GM's Futurama at the 1939 World's Fair was basically of this design. The primary differences are that the crossing freeway is elevated to the extent that all ramps are able to pass beneath it, and it appears there are "express"  lanes in the center that do not have access to the ramps. (Jump to 12:11)

[wxfree]

Here's another "what is this?" I ran into a few days ago.  The frontage roads, which are one-way, have only RIROs, and only one maneuver, a U-turn, has more than one stop, which I guess are advantages.  Movements are clearly signed, but in this case my habit of analyzing road configurations was a disadvantage because it led me to confusion since I wasn't just following the signs but wanted to understand the road layout.  It took me a few seconds to estimate a picture of it.  I was going southbound to eastbound, and that T-intersection was something I wasn't expecting.

If the overpass were in line with the main road, it would function nearly the same way with a set of jug handles, or a U-turn curve on the west side with a cut for the little gravel road.  In this case, the westbound turning lane goes straight ahead and the main road uses the jug handle.  I kinda want to call it an offset jug handle.

https://www.google.com/maps/@32.2716064,-96.5130823,496m/data=!3m1!1e3?hl=en

[froggie]

^ The bridge location is an abnormalty.  But as far as traffic on I-45 is concerned, it's a typical Texas diamond interchange onto the frontage roads.

[Tom958]

This layout is called a Bel Geddes interchange after Norman Bel Geddes, the famous designer who invented it. The idea was that even turning vehicles would be able to pass through it at speed, though it seems likely that he didn't pay enough attention to the downsides of left-hand on- and offramps. Believe it or not, the interchange of I-485 and the GA 400 and 410 tollways in Atlanta, now the site of the Carter Center, was to be of this type.

I'm taken aback at this interchange being described as "ghetto," since the original intent was to maximize speeds at the expense of other factors. However, the double-crossing directional interchange, like Malfunction Junction in Birmingham, could be labeled a ghetto version of the Bel Geddes interchange.

It's at I-40 and I-44 in Oklahoma City. It functions as a complete freeway to freeway interchange but it has left entrances and exits. It was obviously built on the cheap so you could call it a "ghetto interchange" or a "welfare stack". At least it isn't a cloverleaf.

Nexus 5X

[mrsman]

This layout is called a Bel Geddes interchange after Norman Bel Geddes, the famous designer who invented it. The idea was that even turning vehicles would be able to pass through it at speed, though it seems likely that he didn't pay enough attention to the downsides of left-hand on- and offramps. Believe it or not, the interchange of I-485 and the GA 400 and 410 tollways in Atlanta, now the site of the Carter Center, was to be of this type.

I'm taken aback at this interchange being described as "ghetto," since the original intent was to maximize speeds at the expense of other factors. However, the double-crossing directional interchange, like Malfunction Junction in Birmingham, could be labeled a ghetto version of the Bel Geddes interchange.

It's at I-40 and I-44 in Oklahoma City. It functions as a complete freeway to freeway interchange but it has left entrances and exits. It was obviously built on the cheap so you could call it a "ghetto interchange" or a "welfare stack". At least it isn't a cloverleaf.

Nexus 5X

This interchange is actually very good.  For each left hand ramp, you are placed on the left lane of the new freeway with no requirement for a merge.  You can merge right later, when needed.

The nice thing is that it is very smooth, no sharp curves as you'd find in many interchanges.  And FWIW, if there is heavy merging traffic, the effects are mitigated since the merging happens at both left and right, as opposed to both ramps merging in on the right.

[kphoger]

Here's another "what is this?" I ran into a few days ago.  The frontage roads, which are one-way, have only RIROs, and only one maneuver, a U-turn, has more than one stop, which I guess are advantages.  Movements are clearly signed, but in this case my habit of analyzing road configurations was a disadvantage because it led me to confusion since I wasn't just following the signs but wanted to understand the road layout.  It took me a few seconds to estimate a picture of it.  I was going southbound to eastbound, and that T-intersection was something I wasn't expecting.

If the overpass were in line with the main road, it would function nearly the same way with a set of jug handles, or a U-turn curve on the west side with a cut for the little gravel road.  In this case, the westbound turning lane goes straight ahead and the main road uses the jug handle.  I kinda want to call it an offset jug handle.

https://www.google.com/maps/@32.2716064,-96.5130823,496m/data=!3m1!1e3?hl=en

I like to think of that as a "middle of nowhere Texas" interchange.  But they also exist in suburban environments.