Is this interchange classified as a SPUI?

[kphoger]

I disagree.  A tight diamond still has two separate intersections, right?  This is just one intersection – a "single point" – it's just pinched in such a way that two opposite left turns interfere with one another.

Yeah, I thought of that after I'd left the house.  OTOH, tight diamonds basically function as one intersection anyway.  Perhaps you did describe it best a few posts ago.

Regarding whether it's an interchange, the ramps for adjacent interchanges seem to be swapped and/or interlaced.

Those are called X ramps, and are somewhat common in urban environments where frontage roads are present.

[roadfro]

It's still effectively a SPUI. For the frontage roads, think of it more like a SPUI with split phasing on the ramps. Definitely not the preferred operation, though; surely if geometry were better those left turns would be simultaneous.

Go to street view - the left turn paths from the frontage roads cross.

And this is what makes it not a SPUI.  It's just a tight diamond with turnarounds.

I disagree.  A tight diamond still has two separate intersections, right?  This is just one intersection – a "single point" – it's just pinched in such a way that two opposite left turns interfere with one another.

I'd agree. The operation is much closer to a SPUI than it is to a TDI.

The arterial lefts can still proceed together at this one, which still lends to being a SPUI from that aspect.

[jeffandnicole]

It's not even an interchange. There are no ramps to/from the highway here.

Apparently I can't say 'what' in response to this, despite being a completely 'what'-worthy post.

Allow me:  what

jeffandnicole, you apparently didn't scroll enough north or south to see slip ramps in both directions.  The northern ones are south of Bob Wallace Ave, and the southern ones–actually, there are two sets north of Airport Rd.  It's a typical frontage road interchange.

I did scroll both above and below.  The whole definition of a SPUI is a single point urban interchange.  Slip ramps onto a frontage road have nothing to do with a SPUI.  The interchanges for the highway are the slip ramps. Below the highway is nothing more than an everyday intersection with a wide median.

[kphoger]

It's not even an interchange. There are no ramps to/from the highway here.

Apparently I can't say 'what' in response to this, despite being a completely 'what'-worthy post.

Allow me:  what

jeffandnicole, you apparently didn't scroll enough north or south to see slip ramps in both directions.  The northern ones are south of Bob Wallace Ave, and the southern ones–actually, there are two sets north of Airport Rd.  It's a typical frontage road interchange.

I did scroll both above and below.  The whole definition of a SPUI is a single point urban interchange.  Slip ramps onto a frontage road have nothing to do with a SPUI.  The interchanges for the highway are the slip ramps. Below the highway is nothing more than an everyday intersection with a wide median.

By those definitions, then, I-35 between San Antonio and Austin (Loop 1604 to TX-45) has no interchanges, because crossroads served by frontage road slips don't count as interchanges.  I find that narrow definition of an interchange to be untenable.  A diamond interchange doesn't stop being a diamond interchange just because there are frontage roads, so why should a SPUI stop being a SPUI for the same reason?

[johndoe]

A diverging single-point interchange would fail to accommodate left turns exiting the freeway in two-phase mode because there's zero capacity for the cars to wait between the two intersections that are now one.  Also, the striping for through traffic would be really weird.

Can you draw what you mean by this?

[vtk]

A diverging single-point interchange would fail to accommodate left turns exiting the freeway in two-phase mode because there's zero capacity for the cars to wait between the two intersections that are now one.  Also, the striping for through traffic would be really weird.

Can you draw what you mean by this?

Sounds like a fun challenge. I'll tackle it tonight or tomorrow.

[jeffandnicole]

It's not even an interchange. There are no ramps to/from the highway here.

Apparently I can't say 'what' in response to this, despite being a completely 'what'-worthy post.

Allow me:  what

jeffandnicole, you apparently didn't scroll enough north or south to see slip ramps in both directions.  The northern ones are south of Bob Wallace Ave, and the southern ones—actually, there are two sets north of Airport Rd.  It's a typical frontage road interchange.

I did scroll both above and below.  The whole definition of a SPUI is a single point urban interchange.  Slip ramps onto a frontage road have nothing to do with a SPUI.  The interchanges for the highway are the slip ramps. Below the highway is nothing more than an everyday intersection with a wide median.

By those definitions, then, I-35 between San Antonio and Austin (Loop 1604 to TX-45) has no interchanges, because crossroads served by frontage road slips don't count as interchanges.  I find that narrow definition of an interchange to be untenable.  A diamond interchange doesn't stop being a diamond interchange just because there are frontage roads, so why should a SPUI stop being a SPUI for the same reason?

Because it's not a single point interchange.  If anything it's more like the diamond ramps you mention leading to the frontage road. 

[NE2]

This is a SPUI:
http://maps.google.com/maps?ll=27.915947,-82.729427&spn=0.005155,0.007086&gl=us&t=k&z=18
http://books.google.com/books?id=t0jfX9fK5oUC&pg=PA37 (figure 51)

If you disagree you're wrong.

[kphoger]

Because it's not a single point interchange.

Yes it is.  The "single point" part is about the intersection above or below the highway.  The fact that the frontage roads split off from the ramps doesn't enter into it.

Below is the basic layout of the interchange in question.  Look at the bold lines and not the thin lines:  if it weren't for the left-turn paths crossing, it would be a normal SPUI with surface-level through movements added.

[vtk]

A diverging single-point interchange would fail to accommodate left turns exiting the freeway in two-phase mode because there's zero capacity for the cars to wait between the two intersections that are now one.  Also, the striping for through traffic would be really weird.

Can you draw what you mean by this?

Single-Point Diverging Diamond Interchange:



It's really awkward.  It can't operate in two-phase mode.  It requires a lot of bridge deck.  Essentially, this design offers no advantage at all over a standard SPUI or DDI.

[johndoe]

Haha, ok.  It's just a DCD (doesn't that name make more sense than DDI?) with zero storage.  Or a SPUI without concurrent arterial throughs.  But still a huge bridge.  The worst of both worlds!   
What program did you draw that in?

Perhaps you'd enjoy this site, if you haven't seen it before:
http://midimagic.sgc-hosting.com/diamseq.htm

[Alps]

A diverging single-point interchange would fail to accommodate left turns exiting the freeway in two-phase mode because there's zero capacity for the cars to wait between the two intersections that are now one.  Also, the striping for through traffic would be really weird.

Can you draw what you mean by this?

Single-Point Diverging Diamond Interchange:



It's really awkward.  It can't operate in two-phase mode.  It requires a lot of bridge deck.  Essentially, this design offers no advantage at all over a standard SPUI or DDI.

My thought was to offer the same sort of storage as a DDI - shift the crossovers well to the outside, and have the right turn ramps follow along. The difference is having the left turns operate across from each other at a point. It's horribly inefficient compared to a regular DDI, but someone said it couldn't be done, or maybe I just got over-creative.

[NE2]

My thought was that a DDI is already effectively SPUIed, since opposing left turns don't cross.

[jeffandnicole]

This is a SPUI:
http://maps.google.com/maps?ll=27.915947,-82.729427&spn=0.005155,0.007086&gl=us&t=k&z=18
http://books.google.com/books?id=t0jfX9fK5oUC&pg=PA37 (figure 51)

If you disagree you're wrong.

Fine...I'll agree.  I may do it kicking and screaming, but I'll agree.

[vtk]

Haha, ok.  It's just a DCD (doesn't that name make more sense than DDI?) with zero storage.  Or a SPUI without concurrent arterial throughs.  But still a huge bridge.  The worst of both worlds!   
What program did you draw that in?

Engineered in IMSI TurboCAD Deluxe v10.  Illustrated in Jasc Paint Shop Pro 8.

Perhaps you'd enjoy this site, if you haven't seen it before:
http://midimagic.sgc-hosting.com/diamseq.htm

That site is nifty. I'd like to see practical examples of the different variants described there.

My thought was to offer the same sort of storage as a DDI - shift the crossovers well to the outside, and have the right turn ramps follow along. The difference is having the left turns operate across from each other at a point. It's horribly inefficient compared to a regular DDI, but someone said it couldn't be done, or maybe I just got over-creative.

I think I'd have to call that a triple-point diverging diamond.  And it might be worth trying to draw one.

Or, maybe by spreading out the conflict points and timing the signals just right, a 2-phase operation with concurrent movements and no dependence on storage can be achieved.  I suppose that would basically be a CFI decked over a freeway with frontage ramps a couple of blocks away...

[yakra]

My thought was that a DDI is already effectively SPUIed, since opposing left turns don't cross.

wot