I was thinking about this the other day. We are seeing more DDIs popping up around the country. I love them for how safe they seem to be for the average motorist. But another more recent entry into the interchange types are what I call the Paperclip Interchanges. I'm sure there is a formal name for them but I don't know what it is. Anyway, here is an example of a Paperclip at I-41/43/894 and 27th St in Milwaukee.
https://www.google.com/maps/@42.9554878,-87.9490247,730a,35y,44.78t/data=!3m1!1e3!5m1!1e1?entry=ttu
The pro to this seems to be less of a footprint needed especially in an urban area.
The con I am guessing these are more expensive because of the 2 additional bridges.
Anyone know what the formal name is?
And does anyone have any engineering knowledge about the cost of these and the feasibility of these vs a DDI?
Thanks.
It only solves half the problem. It eliminates (in this case) left turns to enter the freeway, but not to exit it. To do the latter would take two more ramps, basically turning it into a full stack scrunched into a narrow space along the freeway. This looks to me like a specific solution to a specific situation, not a general solution. Are there other examples of this?
Quote from: pderocco on July 12, 2024, 11:41:17 AMIt only solves half the problem. It eliminates (in this case) left turns to enter the freeway, but not to exit it. To do the latter would take two more ramps, basically turning it into a full stack scrunched into a narrow space along the freeway. This looks to me like a specific solution to a specific situation, not a general solution. Are there other examples of this?
Not that I am aware of. I thought it may be elsewhere because of the symmetry of the design.
Quote from: pderocco on July 12, 2024, 11:41:17 AMIt only solves half the problem. It eliminates (in this case) left turns to enter the freeway, but not to exit it. To do the latter would take two more ramps, basically turning it into a full stack scrunched into a narrow space along the freeway. This looks to me like a specific solution to a specific situation, not a general solution. Are there other examples of this?
I immediately thought of I-395 at VA-7 (https://www.google.com/maps/@38.8346094,-77.0975526,17.75z?entry=ttu) in the City of Alexandria, Virginia. I've always liked the way that interchange is designed because it eliminates the weave areas that plague the cloverleaf design while nevertheless not requiring left turns and the associated traffic lights.
Quote from: pderocco on July 12, 2024, 11:41:17 AMIt only solves half the problem. It eliminates (in this case) left turns to enter the freeway, but not to exit it. To do the latter would take two more ramps, basically turning it into a full stack scrunched into a narrow space along the freeway. This looks to me like a specific solution to a specific situation, not a general solution. Are there other examples of this?
It functions essentially as a parclo a4, perhaps a bit better since traffic taking the left-turn equivalent to get on the freeway can bypass the stoplight.
You have the Milwaukee A version (similar to a Parclo A4) and a Milwaukee B version (similar to a Parclo B4). I don't believe the Milwaukee B version exists anywhere but it would be pretty cool to see it built.
There has to be a way to combine those to make a version that eliminates all left turns. I think it would be possible but you might have to increase the footprint just a bit to accommodate the weaves that would ensue.
And 'Paperclip' is a great name for that specific interchange in Wisconsin, even if the design never makes it to mainstream use elsewhere.
The Milwaukee B4 eliminates all left turns coming off the freeway. Drivers would still have to make a left to enter the freeway but making a left from an arterial street is pretty common to begin with. You could definitely eliminate all left turns in the Milwaukee A4 design but it would require two additional loop ramps weaved inside the existing loop ramps.
(https://i.imgur.com/wh4sd3w.png)
^^^^
That is essentially what I linked in reply #3, though the version you cite is somewhat more squared-off or distended.
Quote from: webny99 on July 12, 2024, 10:52:20 PMThere has to be a way to combine those to make a version that eliminates all left turns. I think it would be possible but you might have to increase the footprint just a bit to accommodate the weaves that would ensue.
And 'Paperclip' is a great name for that specific interchange in Wisconsin, even if the design never makes it to mainstream use elsewhere.
Probably not the best way to do it, but I-91/US 5 in West Springfield is kind of what you're describing:
https://maps.app.goo.gl/PAWDqcE87yFGcZRG8
This works reasonably well, and certainly much better than a cloverleaf (and required a lot less taking of businesses along US 5). The only problem is that traffic exiting to US 5 SB backs up from the stoplight at the end of that ramp, and this sometimes gets bad enough that US 5 SB-to-I-91 SB (compass east) traffic faces a line of stopped traffic as it tries to get under the bridge and onto the onramp.
Quote from: dantheman on July 16, 2024, 05:58:52 PMQuote from: webny99 on July 12, 2024, 10:52:20 PMThere has to be a way to combine those to make a version that eliminates all left turns. I think it would be possible but you might have to increase the footprint just a bit to accommodate the weaves that would ensue.
...
Probably not the best way to do it, but I-91/US 5 in West Springfield is kind of what you're describing:
https://maps.app.goo.gl/PAWDqcE87yFGcZRG8
This works reasonably well, and certainly much better than a cloverleaf (and required a lot less taking of businesses along US 5). The only problem is that traffic exiting to US 5 SB backs up from the stoplight at the end of that ramp, and this sometimes gets bad enough that US 5 SB-to-I-91 SB (compass east) traffic faces a line of stopped traffic as it tries to get under the bridge and onto the onramp.
Yes, this is pretty much exactly what I was picturing! In fact I may have even subconsciously had this interchange in the back of my mind since I remember having noticed it before. The only thing that I would improve are the short weave areas on the mainline. Ideally you would have C/D roads starting where the outer off-ramps start and ending where the outer on-ramps end. This would require a bit wider bridges but would be easier to navigate and help maintain traffic flow on the mainline.
The stoplight backing up would ideally be solved by having no stoplight and just a direct ramp to the mainline of US 5 SB, but I'm not sure how practical/feasible that would be here. It seems to work on the northbound side so it could probably work if you had the ramp contribute a through lane.
Quote from: tradephoric on July 12, 2024, 10:14:09 PMYou have the Milwaukee A version (similar to a Parclo A4) and a Milwaukee B version (similar to a Parclo B4). I don't believe the Milwaukee B version exists anywhere but it would be pretty cool to see it built.
There really isn't a point to the Milwaukee B version. It requires a wider overpass to accommodate the turn lanes. It also requires 3 phases for the signals.
Quote from: Bitmapped on July 16, 2024, 09:55:33 PMThere really isn't a point to the Milwaukee B version. It requires a wider overpass to accommodate the turn lanes. It also requires 3 phases for the signals.
The Milwaukee B could be done with a two phase signal - I don't think left turns allowed from the exit ramp. Using the northern intersection:
1) WB right turn and NB left turn (go with Phases 1 and 5 for a NEMA signal)
2) NB and SB thru movements (go with Phase 2 and 6 for a NEMA signal)
Pretty sure with the right programming the NB left and WB right could be brought up independently as needed with the non-conflicting traffic not having to stop.
The Milwaukee B could be easier to coordinate on the arterial.
Quote from: dantheman on July 16, 2024, 05:58:52 PMQuote from: webny99 on July 12, 2024, 10:52:20 PMThere has to be a way to combine those to make a version that eliminates all left turns. I think it would be possible but you might have to increase the footprint just a bit to accommodate the weaves that would ensue.
And 'Paperclip' is a great name for that specific interchange in Wisconsin, even if the design never makes it to mainstream use elsewhere.
Probably not the best way to do it, but I-91/US 5 in West Springfield is kind of what you're describing:
https://maps.app.goo.gl/PAWDqcE87yFGcZRG8
This works reasonably well, and certainly much better than a cloverleaf (and required a lot less taking of businesses along US 5). The only problem is that traffic exiting to US 5 SB backs up from the stoplight at the end of that ramp, and this sometimes gets bad enough that US 5 SB-to-I-91 SB (compass east) traffic faces a line of stopped traffic as it tries to get under the bridge and onto the onramp.
Now that does look more efficient. The footprint doesn't look too bad either.
Of all the examples shown on the thread, the I-395 example in Alexandria, is the best. It is clean and there is no weaving.
An ideal interchange in my opinion has the four ramps in the following order: Exit, exit, entrance, entrance. If the order changes, then we have a problem with weaving which seems terrible on the I-91/US5 interchange. The weave area seems smaller than most cloverleafs.
Does it make sense to have the exit ramps merging together before hitting the street as opposed to separate ramps in each direction? It seems like an unnecessary merging practice. Yes, both ramps lead to a right turn, but what if there is a need to turn right or next on the next block, the traffic will have to cross each other.
I'm not very big on DDI's as a general improvement. While it is a good practice in certain circumstances and is helpful with some of the left turns both for entering and exiting the highway, having both directions of traffic cross each other at a signal definitely will slow down traffic on the street. DDI's should only be used if freeway to street traffic (or vice versa) is the dominant flow of the interchange, but in most cases, most traffic on the street will continue onto the street, not merge with the freeway.
Again, the 395/VA 7 interchange seems to take care of a lot of our concerns. It has all of the right turn movements of a cloverleaf in a narrower footprint, while avoiding the worst of the weaving movements.
Quote from: mrsman on July 17, 2024, 01:22:21 PMAn ideal interchange in my opinion has the four ramps in the following order: Exit, exit, entrance, entrance. If the order changes, then we have a problem with weaving which seems terrible on the I-91/US5 interchange. The weave area seems smaller than most cloverleafs.
Fair point on the weaving issue. It is better than a cloverleaf in that there's only weaving on one of the highways (91) instead of both, but weaving on the interstate is arguably worse than on a local road anyway. The weave is not a huge issue here because the "left-turn" exit movements (91 NB to 5 SB and 91 SB to 5 NB) are not heavily used, but it can slow down traffic a bit as people merge from the onramps before they're fully up to speed.
For the VA 7 / I-395 example, while providing free-flow is ideal, the footprint required is larger than the Milwaukee example. The VA 7 interchange has a lot more room between the adjacent interchanges. I don't think you'd be able to build that in the Milwaukee example without creating weaving issues with other interchanges or building it with tighter or substandard curves.
It appears that the first DDI interchange in the US (I-44 & MO 13 in Springfield, MO) is slated for reconstruction eventually because of increasing traffic, and a recently built DDI in Sarasota, FL (I-75 & University Parkway) seems to be failing based on videos showing traffic backing up through the DDI. It looks like we're starting to see where the ceilings are for DDI interchanges regarding their functionality.
I think a downside that might start to crop up with DDI's is that after they braid the over/underpass, they become more difficult to go back and fix. I think it might be possible to have a hybrid DDI/Parclo A4, but otherwise I think you'd have to employ flyovers if a certain movement is collapsing the interchange.
^^^^
I believe that assesment is correct.
The Milwaukee interchange is basically a compressed parclo A4, where the loop ramps are done over/under the freeway as opposed to next to the freeway.
DDI has its limiations because usually the biggest traffic movement at the intersection is the through movement of the arterial, not the movement between arterial and freeway. Introducing a couple left turns (either A style or B style) is usually not bad compared with making the entire movement stop for the reverse movement as they cross each other.
Parclo B4 is probably more efficient in nearly all cases than a DDI.
Half paperclip interchange, (https://www.google.com/maps/@47.201388,-122.2601949,525m/data=!3m1!1e3?entry=ttu) WA 167 and 410, Sumner. Think of it as a folded trumpet interchange requiring two crossings of the through road. The curve is unexpectedly tight to drive.
Quote from: ErmineNotyours on July 24, 2024, 06:22:38 PMHalf paperclip interchange, (https://www.google.com/maps/@47.201388,-122.2601949,525m/data=!3m1!1e3?entry=ttu) WA 167 and 410, Sumner. Think of it as a folded trumpet interchange requiring two crossings of the through road. The curve is unexpectedly tight to drive.
Kind of like this (https://www.google.com/maps/@38.9824454,-76.5575418,638m/data=!3m1!1e3!5m1!1e1?entry=ttu) at US 50 and MD 665 in Annapolis.