Most Roadgeeks know what a Diverging Diamond Interchange is, but for those who don't:
(https://i.imgur.com/X1RckGV.gif)
What it does is force drivers crossing over a freeway to briefly crossover to the wrong side of the road. This allows left turns to be made without crossing the opposing traffic. They've been spreading like wildfire in the last 15 years due to the safety and traffic flow benefits they offer.
But there have been ideas for improving on the DDI.
(https://i.imgur.com/UySxAl5.png)
A relatively simple one is to add left turn loops and make it a Diverging Partial Cloverleaf. The benefit of this is it eliminates the weaving of left turns.
(https://i.imgur.com/Fyxph2z.png)
Another idea is to get rid of the crossover for drivers going straight but keep for those who are turning left. The designer (http://www.cowyite.org/presentations/Smith%20-%20DDI.pdf) describes it as a Splintered Untwisted DDI. This gets rid of a current problem with DDIs in that they can't allow traffic go straight in both directions at the same time. But it does require a wide (read: expensive) bridge structure
(https://i.imgur.com/iU9oQVH.jpg)
And another idea is to grade separate the crossovers. The patent holder (https://patents.google.com/patent/US20130011190A1/en) describes it as a "Double Crossover Merging Interchange". This makes the DDI into a free-flow interchange and thanks to the way that left turns off the freeway rejoin the mainlines, it eliminates weaving. But of course, flyovers are very expensive. Also, if you take two of these, you get a diverging windmill interchange.
These are all very interesting designs and I hope we see them on the road some day.
Neat!
Much more expensive though.
Quote from: jeffandnicole on November 25, 2020, 05:39:34 PM
Much more expensive though.
...and cost is a big reason departments opt for the DDI in the first place.
Quote from: kphoger on November 25, 2020, 06:10:29 PM
Quote from: jeffandnicole on November 25, 2020, 05:39:34 PM
Much more expensive though.
...and cost is a big reason departments opt for the DDI in the first place.
No it's not, a normal diamond interchange is cheaper. The DDI is favored because it gets rid of left turns across the opposing flow of traffic, which vastly improves safety and capacity.
^ Yes, cost is still a deciding factor. SPUIs are more efficient and higher capacity than DDIs but DDIs can be retrofitted into existing diamond interchanges much more easily.
Quote from: kernals12 on November 25, 2020, 04:51:57 PMpatent holder (https://patents.google.com/patent/US20130011190A1/en) describes it as a "Double Crossover Merging Interchange". This makes the DDI into a free-flow interchange and thanks to the way that left turns off the freeway rejoin the mainlines, it eliminates weaving. But of course, flyovers are very expensive. Also, if you take two of these, you get a diverging windmill interchange.
I'd love to see this built! It would be fun to use at locations where one freeway does a crossover on itself before meeting another. (cough cough...I-77 at I-85)
Quote from: Henry on November 25, 2020, 08:35:29 PM
Quote from: kernals12 on November 25, 2020, 04:51:57 PMpatent holder (https://patents.google.com/patent/US20130011190A1/en) describes it as a "Double Crossover Merging Interchange". This makes the DDI into a free-flow interchange and thanks to the way that left turns off the freeway rejoin the mainlines, it eliminates weaving. But of course, flyovers are very expensive. Also, if you take two of these, you get a diverging windmill interchange.
I'd love to see this built! It would be fun to use at locations where one freeway does a crossover on itself before meeting another. (cough cough...I-77 at I-85)
It also seems to require less right of way than most other free flowing interchanges.
Quote from: Henry on November 25, 2020, 08:35:29 PM
Quote from: kernals12 on November 25, 2020, 04:51:57 PMpatent holder (https://patents.google.com/patent/US20130011190A1/en) describes it as a "Double Crossover Merging Interchange". This makes the DDI into a free-flow interchange and thanks to the way that left turns off the freeway rejoin the mainlines, it eliminates weaving. But of course, flyovers are very expensive. Also, if you take two of these, you get a diverging windmill interchange.
I'd love to see this built! It would be fun to use at locations where one freeway does a crossover on itself before meeting another. (cough cough...I-77 at I-85)
Michigan used to have one where both freeways did crossovers. US 131 at I-96 maybe? I'm pretty sure it was changed like ten years ago or something.
Quote from: vtk on November 26, 2020, 01:22:31 AM
Quote from: Henry on November 25, 2020, 08:35:29 PM
Quote from: kernals12 on November 25, 2020, 04:51:57 PMpatent holder (https://patents.google.com/patent/US20130011190A1/en) describes it as a "Double Crossover Merging Interchange". This makes the DDI into a free-flow interchange and thanks to the way that left turns off the freeway rejoin the mainlines, it eliminates weaving. But of course, flyovers are very expensive. Also, if you take two of these, you get a diverging windmill interchange.
I'd love to see this built! It would be fun to use at locations where one freeway does a crossover on itself before meeting another. (cough cough...I-77 at I-85)
Michigan used to have one where both freeways did crossovers. US 131 at I-96 maybe? I'm pretty sure it was changed like ten years ago or something.
US-131 crosses over itself at I-196, but I-196 doesn't cross over. Lot of left exits and entrances. And that high-in-the-air ramp from sb to wb is kind of scary; you're looking into the 4th floor windows of the old school to the right.
Quote from: kernals12 on November 25, 2020, 06:36:32 PM
Quote from: kphoger on November 25, 2020, 06:10:29 PM
Quote from: jeffandnicole on November 25, 2020, 05:39:34 PM
Much more expensive though.
...and cost is a big reason departments opt for the DDI in the first place.
No it's not, a normal diamond interchange is cheaper. The DDI is favored because it gets rid of left turns across the opposing flow of traffic, which vastly improves safety and capacity.
A simple litmus test is this: Does MoDOT construct them frequently? If the answer is
YES, then cost is definitely a factor.
UDOT has built a couple interchanges that resemble something between a DDI and CFI, with a crossover only for one on-ramp. The I-15 interchanges at SR 93 (https://www.google.com/maps/@40.8613169,-111.9027464,472m/data=!3m1!1e3)and at SR 103 (https://www.google.com/maps/@41.1235657,-112.0240667,281m/data=!3m1!1e3) both use this design. Not quite sure what to make of them.
I once designed and built a folded DDI in C:S, but it was messy and didn't look good. Also, it was expensive.
Quote from: US 89 on November 27, 2020, 12:37:00 PM
UDOT has built a couple interchanges that resemble something between a DDI and CFI, with a crossover only for one on-ramp. The I-15 interchanges at SR 93 (https://www.google.com/maps/@40.8613169,-111.9027464,472m/data=!3m1!1e3)and at SR 103 (https://www.google.com/maps/@41.1235657,-112.0240667,281m/data=!3m1!1e3) both use this design. Not quite sure what to make of them.
Thanks for posting, I only knew of 1 of those 2. I think it was highlighted in an industry magazine; how'd you stumble across them? Anyone know of more examples? Texas has a few similar to that (although the crossover happens a little differently so not sure it counts as DDI...) a couple in San Marcos and Bandera Road in San Antonio.
Missouri has another sort of CFI-DDI combo and two "half-DDI half roundabout".
That "splintered" idea is shown in this presentation: http://www.cowyite.org/presentations/Smith%20-%20DDI.pdf
Here's a thread of another variation, where they added the frontage road "through" movements in Florida: https://www.aaroads.com/forum/index.php?topic=27649.0
And yes... I promise cost is a big reason a lot of these things happen. Bridges are very expensive, so less is more!
Quote from: johndoe on November 27, 2020, 11:02:05 PM
Quote from: US 89 on November 27, 2020, 12:37:00 PM
UDOT has built a couple interchanges that resemble something between a DDI and CFI, with a crossover only for one on-ramp. The I-15 interchanges at SR 93 (https://www.google.com/maps/@40.8613169,-111.9027464,472m/data=!3m1!1e3)and at SR 103 (https://www.google.com/maps/@41.1235657,-112.0240667,281m/data=!3m1!1e3) both use this design. Not quite sure what to make of them.
Thanks for posting, I only knew of 1 of those 2. I think it was highlighted in an industry magazine; how'd you stumble across them?
Driving through them. I go through the 93 interchange fairly often and knew that one was coming before it got built, as it was part of a bigger project that reconstructed I-15 through the southern third of Davis County. The other one I did not know of before I happened upon it about two years ago while clinching state routes in the area.
Quote from: johndoe on November 27, 2020, 11:02:05 PM
Missouri has another sort of CFI-DDI combo ...
Are you referring to
this one (https://goo.gl/maps/xQMo6WhtbopGsD9z8)?
Quote from: kphoger on November 30, 2020, 02:08:05 PM
Quote from: johndoe on November 27, 2020, 11:02:05 PM
Missouri has another sort of CFI-DDI combo ...
Are you referring to this one (https://goo.gl/maps/xQMo6WhtbopGsD9z8)?
Yep. Not sure if others of those have been built, but Florida and Georgia have at least considered them:
https://www.yourobserver.com/article/public-outreach-meeting-planned-i-75-bee-ridge-construction
http://www.dot.ga.gov/BuildSmart/Studies/ManagedLanesDocuments/OPSFinalReport-Appendices.pdf
(googled things like "displaced left interchange" etc)
https://www.researchgate.net/publication/273887124_Study_of_Alternative_Design
Tacoma's I-705/I-5/SR 7 (https://www.google.com/maps/@47.2328335,-122.4317065,17z?hl=en) interchange has the through lanes south of I-5 switch place to make ramps shorter. I always thought of that as a controlled access DDI.
Quote from: ErmineNotyours on November 30, 2020, 07:50:12 PM
Tacoma's I-705/I-5/SR 7 (https://www.google.com/maps/@47.2328335,-122.4317065,17z?hl=en) interchange has the through lanes south of I-5 switch place to make ramps shorter. I always thought of that as a controlled access DDI.
That's basically like
"El Sarape" interchange (https://goo.gl/maps/ZifVTP5jYymGGLHz7) in Saltillo, Coahuila.
Do any of these variations actually exist IRL?
With the Folded interchange through traffic on the arterial street aren't forced to cross opposing lanes of traffic leading to an unnecessary and potentially dangerous conflict point. However this design only works if you have enough ROW for loop ramps.
https://www.youtube.com/watch?v=gR-VOJlKjmc
Quote from: kphoger on December 02, 2020, 10:00:16 AM
That's basically like "El Sarape" interchange (https://goo.gl/maps/ZifVTP5jYymGGLHz7) in Saltillo, Coahuila.
I have 2 intersections like that back-to-back in one of my C:S cities.
The DDI at Timpanogos Hwy and I-15 has experienced significant suggestion since opening in 2011. As a result UDOT has decided to tear it down and convert it back to a traditional interchange. Truly taxpayer dollars at work here... building this "innovative" interchange only to tear it out less than 10 years later. Is this the first DDI casualty in America?
https://www.youtube.com/watch?v=CUsMRdxSLdM
Quote from: tradephoric on December 28, 2020, 08:01:30 AM
The DDI at Timpanogos Hwy and I-15 has experienced significant suggestion since opening in 2011. As a result UDOT has decided to tear it down and convert it back to a traditional interchange. Truly taxpayer dollars at work here... building this "innovative" interchange only to tear it out less than 10 years later. Is this the first DDI casualty in America?
https://www.youtube.com/watch?v=CUsMRdxSLdM
Suggestion is intolerable.
Quote from: tradephoric on December 28, 2020, 08:01:30 AM
The DDI at Timpanogos Hwy and I-15 has experienced significant suggestion since opening in 2011. As a result UDOT has decided to tear it down and convert it back to a traditional interchange. Truly taxpayer dollars at work here... building this "innovative" interchange only to tear it out less than 10 years later. Is this the first DDI casualty in America?
https://www.youtube.com/watch?v=CUsMRdxSLdM
It should be noted that the removal was done in conjunction with a major reconstruction of that portion of I-15. That included the installation of about three miles of one-way frontage road...which doesn't really work with a DDI.
Quote from: US 89 on December 28, 2020, 11:44:38 PM
It should be noted that the removal was done in conjunction with a major reconstruction of that portion of I-15. That included the installation of about three miles of one-way frontage road...which doesn't really work with a DDI.
New frontage road does throw a monkey wrench in it and makes the DDI impractical. Just seems wasteful when a major interchange is ripped out less than 10 years from being completed. Where was the planning and development?
Quote from: froggie on November 25, 2020, 07:31:33 PM
^ Yes, cost is still a deciding factor. SPUIs are more efficient and higher capacity than DDIs but DDIs can be retrofitted into existing diamond interchanges much more easily.
Or not. The GA 400-Abernathy Road interchange reconstruction near Atlanta had been proposed as a SPUI since the '90s, but it's now being rebuilt as a DDI. The whole area is under massive reconstruction with the original bridges being removed and replaced, so it's unlikely that cost was a factor. Plus, the GDOT people at the public meetings I attended said it performed better in their modeling.
Quote from: kphoger on December 02, 2020, 10:00:16 AMThat's basically like "El Sarape" interchange (https://goo.gl/maps/ZifVTP5jYymGGLHz7) in Saltillo, Coahuila.
Might as well invoke this one in Aguascalientes (https://www.google.com/maps/@21.9445556,-102.2901958,399m/data=!3m1!1e3?hl=en). It's not nearly as spectacular, but it makes far greater use of the retained cuts and fills that the crazy-small footprint of the grade-separated DDI in the OP implies.
I really think this one's kind of brilliant, though other than the side-swapping roadways, it doesn't compare to a normal signalized DDI.
Quote from: Tom958 on December 29, 2020, 06:02:47 PM
Quote from: froggie on November 25, 2020, 07:31:33 PM
^ Yes, cost is still a deciding factor. SPUIs are more efficient and higher capacity than DDIs but DDIs can be retrofitted into existing diamond interchanges much more easily.
Or not. The GA 400-Abernathy Road interchange reconstruction near Atlanta had been proposed as a SPUI since the '90s, but it's now being rebuilt as a DDI. The whole area is under massive reconstruction with the original bridges being removed and replaced, so it's unlikely that cost was a factor. Plus, the GDOT people at the public meetings I attended said it performed better in their modeling.
In that particular case, perhaps not. But it's well-documented (and done elsewhere) that DDIs can be retrofitted into existing diamond interchanges without the need to replace or expand overpasses.
The DDI at I-85 and Jimmy Carter Blvd outside Atlanta seems too compact. In addition the DDI reduced the travel lanes from 7 to 6 compared to the old diamond interchange while using the same width bridge deck (admittedly the pedestrian path was widened for the DDI but at the expense of a travel lane). Every time Google updates their aerial it just seems like there is a massive traffic jam at this DDI.
(https://i.imgur.com/ymyrbqL.png)
Wait what's going on there with the southbound exit ramp? I see cars entering from both sides of the conflict. Isn't that junction signal-controlled?
Quote from: vtk on March 10, 2021, 01:23:49 PM
Wait what's going on there with the southbound exit ramp? I see cars entering from both sides of the conflict. Isn't that junction signal-controlled?
Tailback from SB-to-EB congestion? That is, perhaps the EB light turned green while cars were still stopped in the conflict point?
Quote from: Tom958 on December 29, 2020, 07:07:44 PM
Quote from: kphoger on December 02, 2020, 10:00:16 AMThat's basically like "El Sarape" interchange (https://goo.gl/maps/ZifVTP5jYymGGLHz7) in Saltillo, Coahuila.
Might as well invoke this one in Aguascalientes (https://www.google.com/maps/@21.9445556,-102.2901958,399m/data=!3m1!1e3?hl=en). It's not nearly as spectacular, but it makes far greater use of the retained cuts and fills that the crazy-small footprint of the grade-separated DDI in the OP implies.
I really think this one's kind of brilliant, though other than the side-swapping roadways, it doesn't compare to a normal signalized DDI.
Problem is, American drivers cant handle something like this
https://goo.gl/maps/ZbFMGXbMHHQFXtPb7
Quote from: jamess on March 11, 2021, 03:55:11 PM
Problem is, American drivers cant handle something like this
https://goo.gl/maps/ZbFMGXbMHHQFXtPb7
If you put the interchange above ground instead of below it, I think that could work here.
Quote from: tradephoric on December 30, 2020, 11:22:03 AM
The DDI at I-85 and Jimmy Carter Blvd outside Atlanta seems too compact. In addition the DDI reduced the travel lanes from 7 to 6 compared to the old diamond interchange while using the same width bridge deck (admittedly the pedestrian path was widened for the DDI but at the expense of a travel lane). Every time Google updates their aerial it just seems like there is a massive traffic jam at this DDI.
(https://i.imgur.com/ymyrbqL.png)
The shoulders on I-85 seem substandard, too.
Quote from: tradephoric on December 30, 2020, 11:22:03 AM
The DDI at I-85 and Jimmy Carter Blvd outside Atlanta seems too compact. In addition the DDI reduced the travel lanes from 7 to 6 compared to the old diamond interchange while using the same width bridge deck (admittedly the pedestrian path was widened for the DDI but at the expense of a travel lane). Every time Google updates their aerial it just seems like there is a massive traffic jam at this DDI.
(https://i.imgur.com/ymyrbqL.png)
I've been at this one at 95 and GA 21 a few times, and same thing. While it doesn't show any traffic in the aerial, I've only encountered jams and long waits at this DDI. Again, as above, there's a lot going on in a short distance. I've been in this area because gas tends to be cheaper than elsewhere for a distance, and once I get off the exit I realize why I hate getting off the exit. I really can't see the benefit of the DDI here.
Quote from: tradephoric on December 30, 2020, 11:22:03 AM
The DDI at I-85 and Jimmy Carter Blvd outside Atlanta seems too compact. In addition the DDI reduced the travel lanes from 7 to 6 compared to the old diamond interchange while using the same width bridge deck (admittedly the pedestrian path was widened for the DDI but at the expense of a travel lane). Every time Google updates their aerial it just seems like there is a massive traffic jam at this DDI.
(https://i.imgur.com/ymyrbqL.png)
One problem I can see right off: the overpass structure is only 3 lanes in each direction (matching the original six-lane setup of the traditional diamond). Not enough space to handle the JCB through traffic and the left turning movements.
The solution would be to widen the overpass to add an additional lane or two in each direction to act as the buffer for weaving movements and allow for three dedicated lanes for straight on JCB traffic.
Also, I noticed that the through lanes in each direction drop a lane to the left turning movements before the switch back to conventional-side movement, meaning only 2 lanes go through before picking up the 3rd lane again from the right-turn entrance. That might be your choke point; need to widen to make it 3 lanes all the way through for consistency, and use acceleration/merging ramps at the on-ramp connection points for better merging.
Though, at this point, a SPUI with extended ramps would probably be more efficient here.
The whole point of a DDI is that it performs really well when the traffic entering and exiting the freeway is significantly greater than the traffic passing through on the surface street. Under such conditions, having three travel lanes each way reduced to two at the interchange should not be an issue. I can't tell from the photo whether it's a problem at this interchange, but either way, there's probably no better solution here without spending a lot of money on ROW acquisition and/or new structures.
How about this DDI around a T-intersection north of Las Vegas? Even more amazing is there are no traffic lights (only stop signs)
https://www.google.com/maps/@36.3812266,-114.8930064,465m/data=!3m1!1e3