What's the most original intersection/interchange you've ever seen?

[jakeroot]

Is there any operational advantage of a terminal DDI versus a terminal diamond? Both are two-phase signals, though (in some states) a terminal diamond allows left turns on red.

I'm not sure I understand; there is no signal at the southbound ramps.  A traditional diamond would require one, along with a three phase signal at the northbound ramps (although you wouldn't expect anyone on the off-ramp left).

Terminal diamonds do not permit U-turns (though frankly, I don't see why they need to). Here's an example of how, in terms of phases, terminal diamonds and terminal DDIs are the same:

Traffic drives on the left in this diagram.

[NE2]

Is there any operational advantage of a terminal DDI versus a terminal diamond?

No, except perhaps slightly higher speeds on green.

[davewiecking]

(Posting in reverse for those of us who can't think British on the fly)

[jakeroot]

(Posting in reverse for those of us who can't think British on the fly)

The point is simply to demonstrate how both interchanges have two phases. LHD/RHD is not necessarily relevant (though, to prevent people from commenting on it, I did mention that my diagram was RHD when I first posted it).

[paulthemapguy]

(Posting in reverse for those of us who can't think British on the fly)

I just wanted to say that, it was really clever of you to recognize to just do a mirror image, in order to flip the traffic across the whole diagram.

But I see what you all mean now, when you say there is no advantage to putting a terminal DDI over a terminal diamond.  Some engineer must have just had a boner for DDI's.

[lordsutch]

I think it also allows for a potential extension of the road as well.

I believe that's why VDOT is putting a DDI at the new interchange at US 460 and Southgate Drive in Blacksburg; the ultimate plan is to build a new location roadway to the west as well.

[mrsman]

Is there any operational advantage of a terminal DDI versus a terminal diamond? Both are two-phase signals, though (in some states) a terminal diamond allows left turns on red.

I'm not sure I understand; there is no signal at the southbound ramps.  A traditional diamond would require one, along with a three phase signal at the northbound ramps (although you wouldn't expect anyone on the off-ramp left).

Terminal diamonds do not permit U-turns (though frankly, I don't see why they need to). Here's an example of how, in terms of phases, terminal diamonds and terminal DDIs are the same:

I would say that among the advantages of a DDI are that the left turn on-ramp will be more smooth and so more left turners can make the turn at full speed.  Also, there is likely more space for exiting cars to wait for the light to change and not cause back ups on the main lanes of the expressway.

[Jardine]

{I didn't find a version of the pic without lettering, sorry}

[jakeroot]

https://i.imgflip.com/10pl1g.jpg

I can't quite figure out what interchange that Photoshop is based off of. My original guess was the 110/105 interchange outside Hawthorna, Los Angeles, but the buildings don't match up, and neither do some of the ramp designs. Any ideas?

[vdeane]

(Posting in reverse for those of us who can't think British on the fly)

I just wanted to say that, it was really clever of you to recognize to just do a mirror image, in order to flip the traffic across the whole diagram.

But I see what you all mean now, when you say there is no advantage to putting a terminal DDI over a terminal diamond.  Some engineer must have just had a boner for DDI's.

But wouldn't cars be able to move through faster through the DDI light (remember, at the diamond light, everyone is making a left turn), thereby getting more people though even though the phases are the same length?  It also eliminates the merge with the other ramp by making it signal controlled.

[jakeroot]

But I see what you all mean now, when you say there is no advantage to putting a terminal DDI over a terminal diamond.  Some engineer must have just had a boner for DDI's.

But wouldn't cars be able to move through faster through the DDI light (remember, at the diamond light, everyone is making a left turn), thereby getting more people though even though the phases are the same length?  It also eliminates the merge with the other ramp by making it signal controlled.

The diamond design does possess a left-on-red scenario, which is legal from two-way roads in some states. I could see this being advantageous on occasion.

[NE2]

https://i.imgflip.com/10pl1g.jpg

I can't quite figure out what interchange that Photoshop is based off of. My original guess was the 110/105 interchange outside Hawthorna, Los Angeles, but the buildings don't match up, and neither do some of the ramp designs. Any ideas?

A reverse image search gets me to an LA Examiner article. Then searching for that image gets me here where someone says "It originated from a forum for Dallas architecture. It's poking fun at The High Five on highway 635. Which looks somewhat similar, however obviously not that intricate." But it's definitely not the High Five. I give up; it could be heavily shopped with each area from a different interchange.

[vdeane]

But I see what you all mean now, when you say there is no advantage to putting a terminal DDI over a terminal diamond.  Some engineer must have just had a boner for DDI's.

But wouldn't cars be able to move through faster through the DDI light (remember, at the diamond light, everyone is making a left turn), thereby getting more people though even though the phases are the same length?  It also eliminates the merge with the other ramp by making it signal controlled.

The diamond design does possess a left-on-red scenario, which is legal from two-way roads in some states. I could see this being advantageous on occasion.

Indeed, though that wouldn't help if traffic is high enough that ability to move quickly through the green is more important than whether a left on red could be made (and technically the diamond is a one-way and a two-way, which is legal less often).  That could be moot though - the diagram was made in a country that drives on the left, and I don't know if "left" (right, really) on red is legal in any of those countries.  I'm pretty sure it's a North American concept; while we take turns on red for granted, in many countries any turns on red are strictly illegal.

[roadfro]

Is there any operational advantage of a terminal DDI versus a terminal diamond?

No, except perhaps slightly higher speeds on green.

That was the only advantage I could think of initially.

The only other idea that came to mind was if the terminal DDI is installed at a lower-volume location, you could potentially have one side of the crossover intersection be yield controlled. That could make the whole interchange almost free-flowing if you had an added/acceleration lane from the off ramp to the crossroad on the crossover side. But then again, it seems unlikely that a DOT would install a terminal DDI at a lower-volume interchange to begin with...

[jakeroot]

That could be moot though - the diagram was made in a country that drives on the left, and I don't know if "left" (right, really) on red is legal in any of those countries.  I'm pretty sure it's a North American concept; while we take turns on red for granted, in many countries any turns on red are strictly illegal.

The diagram is RHD because the city that I was working on at the time (in Cities Skylines) was RHD. But, as I said to Paul above, the point is not RHD vs LHD. My diagram was simply to illustrate how both designs have two signal phases.

The only other idea that came to mind was if the terminal DDI is installed at a lower-volume location, you could potentially have one side of the crossover intersection be yield controlled. That could make the whole interchange almost free-flowing if you had an added/acceleration lane from the off ramp to the crossroad on the crossover side. But then again, it seems unlikely that a DOT would install a terminal DDI at a lower-volume interchange to begin with...

I seem to recall a crossover type interchange somewhere in the Northeast with the crossover using a yield sign. Perhaps someone else knows where it was.

[Jet380]

Down here in Australia they've just completed a new sort of interchange, the first of its kind anywhere apparently.


Fact sheet: http://gatewaywa.com.au/assets/Uploads/Roe-Highway-Berkshire-Road-Factsheet.pdf

It's called a 'Tennis Ball Interchange', functionally the same as a standard diamond but... curvy...

According to the Main Roads department, the design will improve safety 'through decreasing the severity of potential impacts by a change in incident angle and a reduction in approach speed.' 

[paulthemapguy]

Down here in Australia they've just completed a new sort of interchange, the first of its kind anywhere apparently.


Fact sheet: http://gatewaywa.com.au/assets/Uploads/Roe-Highway-Berkshire-Road-Factsheet.pdf

It's called a 'Tennis Ball Interchange', functionally the same as a standard diamond but... curvy...

According to the Main Roads department, the design will improve safety 'through decreasing the severity of potential impacts by a change in incident angle and a reduction in approach speed.' 

LOLOLOLOL Look at all the merging issues they're going to have from the cars merging in from the left!  Apparently some engineer has never considered what happens when through traffic wants to exit to one side right after traffic enters the road from that same side, the problem with every basic cloverleaf ever.  They just took right-side weave issues and moved them to the left, unless there's a configuration of signal phases I haven't thought of.

[jeffandnicole]

Down here in Australia they've just completed a new sort of interchange, the first of its kind anywhere apparently.


Fact sheet: http://gatewaywa.com.au/assets/Uploads/Roe-Highway-Berkshire-Road-Factsheet.pdf

It's called a 'Tennis Ball Interchange', functionally the same as a standard diamond but... curvy...

According to the Main Roads department, the design will improve safety 'through decreasing the severity of potential impacts by a change in incident angle and a reduction in approach speed.' 

LOLOLOLOL Look at all the merging issues they're going to have from the cars merging in from the left!  Apparently some engineer has never considered what happens when through traffic wants to exit to one side right after traffic enters the road from that same side, the problem with every basic cloverleaf ever.  They just took right-side weave issues and moved them to the left, unless there's a configuration of signal phases I haven't thought of.

For starters, they drive on the opposite side of the road (compared to USA drivers), so their normal merging should be on the left.

Aside from that, I'm not sure where the "Change in incident angles" are at.  Many of the actual intersections are still 90 degree (or very close to it) angles.

And what's with that island separation for traffic coming from the top to the bottom?  I can't see why that's really necessary.

Another thing to consider.  Looks like there's a lot of warehouses there.  Warehouses = trucks.  Trucks prefer straight roads, not tightly curved roads.

[Henry]

The I-85/I-77 interchange in Charlotte also comes to mind. What makes it intriguing is the double-crossover that I-77 does there, allowing the two loop ramps (to I-85) and the two left-turn ramps (from I-85) to be placed in the middle.

And speaking of I-77 in Charlotte, the two junctions with I-277 (at the Brookshire and Belk Freeways) also make an interesting case of their own.

The Cyclone (I-85/I-485) earns an honorable mention

Forgot about that one! It, and I-295/FL 202 in Jacksonville, are copycats of the Chicago example I posted earlier; therefore, I refer to them as Circle South (I for the latter, II for the former).

[jakeroot]

And what's with that island separation for traffic coming from the top to the bottom?  I can't see why that's really necessary.

To help solidify that the right lane is right-turn only. No different than the splitters sometimes seen at roundabouts: https://goo.gl/fzKl47

Another thing to consider.  Looks like there's a lot of warehouses there.  Warehouses = trucks.  Trucks prefer straight roads, not tightly curved roads.

Australian truckers are pretty used to roundabouts, so I don't think they'll have any trouble getting used to this.

[tradephoric]

Here is a real life example of a terminal DDI:
https://www.google.com/maps/@39.15612,-76.74517,425m/data=!3m1!1e3

[cl94]

Here is a real life example of a terminal DDI:
https://www.google.com/maps/@39.15612,-76.74517,425m/data=!3m1!1e3

Something like that makes a lot of sense, especially if traffic that needs to make the right turn is high.

[tckma]

Here is a real life example of a terminal DDI:
https://www.google.com/maps/@39.15612,-76.74517,425m/data=!3m1!1e3

...which appears to be the exact same one I posted to start off this lively discussion.

[Jardine]

 

[Jet380]

LOLOLOLOL Look at all the merging issues they're going to have from the cars merging in from the left!  Apparently some engineer has never considered what happens when through traffic wants to exit to one side right after traffic enters the road from that same side, the problem with every basic cloverleaf ever.  They just took right-side weave issues and moved them to the left, unless there's a configuration of signal phases I haven't thought of.

I think the point still stands (as long as you reverse the directions  ) but considering the interchange is signalised with all movements protected, it won't really be a 'merging' situation.

And Jakeroot is spot on with the splitters being similar to what you get at roundabouts - they're also made to stop drivers from changing lanes in order to take the corner in more of a 'racing line', thus reducing speeds. The 'speed kills' mentality is king here!