Oldest SPUIs?

[jakeroot]

I don't see how it matters what side of the highway traffic had exited from before reaching the intersection.  Only the intersection itself should matter in defining a SPUI.  As an analogue, I consider I-244 Exit #6A in Tulsa to be a split diamond interchange, even though one half of the diamond is between the I-244 roadways.

Do simultaneous left turns without a straight-on movement really need to be the only defining feature? Because, although that's the key with SPUI's, they're impressive because the ramps usually start on the right and somehow don't overlap.

edit: horrible grammar.

[NE2]

A 1991 book about SPUIs can be downloaded here: http://ntrl.ntis.gov/NTRL/dashboard/searchResults/titleDetail/PB92167113.xhtml
It includes some with frontage roads (e.g. p. 7, p. 35) and talks about the one in Clearwater being first (p. 3), but the authors failed to find the earlier one in Fort Worth.

[johndoe]

I think if I were road-geek-term-king...
SPUI: diamond form of interchange where neither the lefts on to or off of the freeway interlock and a 3-phase signal provides all movements.

Personally I consider an offset SPUI more of a SPUI than the ones with frontage road signal phases, because that 4th signal phase hurts efficiency.  And I guess that goes out the window if the offset SPUI is a roundabout because now your lefts from the freeway hurt each other 

[sprjus4]

An interchange between US-13 (Military Hwy) and US-58 (Virginia Beach Blvd) in Norfolk, VA was constructed in the early 2000s to replace an older cloverleaf that was previously located there, and it's designed and striped like a SPUI (allowing both ramps to turn left at the same time), though also has straight through movements. From my experience driving through there, it seems to simply be timed to allow one off-ramp ramp at a time go both straight and left at once, instead of both left turning movements at the same time like a traditional SPUI.

[jakeroot]

An interchange between US-13 (Military Hwy) and US-58 (Virginia Beach Blvd) in Norfolk, VA was constructed in the early 2000s to replace an older cloverleaf that was previously located there, and it's designed and striped like a SPUI (allowing both ramps to turn left at the same time), though also has straight through movements. From my experience driving through there, it seems to simply be timed to allow one off-ramp ramp at a time go both straight and left at once, instead of both left turning movements at the same time like a traditional SPUI.

I find it interesting that, despite this phasing, signs were installed telling traffic how to perform the double left.

[ztonyg]

An interchange between US-13 (Military Hwy) and US-58 (Virginia Beach Blvd) in Norfolk, VA was constructed in the early 2000s to replace an older cloverleaf that was previously located there, and it's designed and striped like a SPUI (allowing both ramps to turn left at the same time), though also has straight through movements. From my experience driving through there, it seems to simply be timed to allow one off-ramp ramp at a time go both straight and left at once, instead of both left turning movements at the same time like a traditional SPUI.

ADOT in Arizona built dozens of these types of SPUIs in the Phoenix area with frontage roads in the late 1980s - early 2000s. Some of them are timed to allow both off ramps to turn left at the same time while others are timed to allow only one direction to go straight and left at the same time.

[OracleUsr]

Greensboro NC has one that's been there probably as far back as when we first moved back to GSO.  Wendover Ave at Holden Road would probably count as a SPUI since all off and on ramps converge on the same point.  We moved to GSO in 1975.

[hobsini2]

I know the first SPUI in DuPage County was Butterfield Rd (Rt 56) at Highland Ave. I seem to recall that was done around 1988. The oldest on I-55 is the Pulaski Rd exit in Chicago. That one was done in 1997.

[wriddle082]

Memphis/Shelby County, TN is absolutely filled with SPUIs.  I think they have the oldest one in TN at Walnut Grove Rd and Germantown Pkwy, which was built sometime in the 80's.  Then a bunch of other ones were built along TN 385 Bill Morris Pkwy in the 90's and 00's.  Eight SPUI exits in a row once past Hickory Hill Rd, then if you choose to take I-269 north (formerly TN 385), you hit one more.

[Big John]

Moline IL, 7th Ave under I-74

[TheHighwayMan3561]

I-494 at 24th Ave in Bloomington, probably Mall of America related in the early 90s

I-35 at Lake Avenue in Duluth

[MCRoads]

To my knowledge, SPUIs do not have straight movements, except those that do. But I don't know if they're true* SPUIs anymore.

* "true" being the dilemma here; "true" to me is right-side ramps, no straight-ahead movement. It's as much a visual distinction as it is technical. But maybe others disagree.

Here's a SPUI where one direction has a straight-through movement, but the other one doesn't: https://goo.gl/maps/xJvCCxN3mbg5fsvj6

I'm inclined to think it counts, since the main idea is to have a single intersection, but having straight-through movements does add to the signal phase count, so it's debatable.

On another note, here's a Super-2 with a SPUI: https://goo.gl/maps/kbqpNug2GUr3YY91A , and it also has straight-through movements.  I wonder how many of those exist.

Edit: That Super-2 SPUI is also part of a split-diamond.  For some reason, I was having trouble remembering the correct terminology when I mentioned that earlier.

There is a SPUI in Castle Rock, CO that seems like it was built in preparation for the Super-2 it serves to be widened, but it is still a super-2!

In regards to SPUIs with straight movements, at Union and Austin Bluffs Pkwy in Co Spgs, there is a SPUI that has thru movements for busses only! Does that count?

[jakeroot]

There is a SPUI in Castle Rock, CO that seems like it was built in preparation for the Super-2 it serves to be widened, but it is still a super-2!

That's actually one of my favorites, since the left turns have flashing yellow arrows. Permissive turns at SPUIs are pretty rare.

Google Maps link

[Joe The Dragon]

milwaukee/dempster in niles il (kind of??) 1st Build in 1930's??

[Revive 755]

There is a SPUI in Castle Rock, CO that seems like it was built in preparation for the Super-2 it serves to be widened, but it is still a super-2!

That's actually one of my favorites, since the left turns have flashing yellow arrows. Permissive turns at SPUIs are pretty rare.

Google Maps link

Highway 2/Van Dorn Street at US 77 in Lincoln, NE also has a permissive lefts

[jakeroot]

There is a SPUI in Castle Rock, CO that seems like it was built in preparation for the Super-2 it serves to be widened, but it is still a super-2!

That's actually one of my favorites, since the left turns have flashing yellow arrows. Permissive turns at SPUIs are pretty rare.

Google Maps link

Highway 2/Van Dorn Street at US 77 in Lincoln, NE also has a permissive lefts

With excellent visibility, you have to wonder why this isn't more common. The length of a left turn, between the stop line and the clearance point, rarely seems to impact left turn signalization decisions at regular intersections...why at SPUIs? You could theoretically operate a SPUI without any protected left turns, and turn the whole interchange into a two-phase junction.

milwaukee/dempster in niles il (kind of??) 1st Build in 1930's??

Hmmm. SPUIs, as we know them today, typically allow for the off-ramps to proceed at the same time; this example only permits one off-ramp at a time. With that in mind, it seems more like a tight diamond.

[SkyPesos]

From searching on google earth historical images for a bit:

I-270 and Sawmill was upgraded from a diamond to SPUI sometime between 1994 and 2002.
I-465 and Emerson was upgraded from a diamond to SPUI sometime between 1998 and 2003

Those 2 are far from the oldest in the country, but some of the ones older than I am.

[johndoe]

With excellent visibility, you have to wonder why this isn't more common. The length of a left turn, between the stop line and the clearance point, rarely seems to impact left turn signalization decisions at regular intersections.

I'm trying to remember the different guidelines for allowing permissive lefts (something to Google for fun later if you're bored!), but don't recall a factor for really large intersections.  I know the intersection sight distance is based on opposing speed, which would be high in a SPUI.  So my guesses why you don't see SPUI permisssive lefts often:

1. the conflict area is so large (due to the big radius and median width) and opposing speeds are so high that drivers won't generally be able to see far enough to judge that gap.  For instance on the Nebraska example it looks like the conflict area is more than 100' from the stop line to beyond the opposing throughs.  At most SPUI I don't think you'd really have any chance to pull into the intersection due to the large radius.

2. Many SPUI are on the crest of a vertical curve.  Drivers trying to look for cars coming over a hill toward them on a tangent (fast) could lead to right angle crashes at relatively high speed - potentially serious crashes.

3.  Many SPUI don't have "positive offset" (another fun Google topic!) for the opposing lefts.  Basically someone trying to turn left the other direction will block your view of the throughs you need to yield to.

[Hot Rod Hootenanny]

From searching on google earth historical images for a bit:

I-270 and Sawmill was upgraded from a diamond to SPUI sometime between 1994 and 2002.

I can tell you that the change from diamond to SPUI, for Sawmill @ I-270 occurred at the start of the 21st Century and was completed in 2002.

[jakeroot]

With excellent visibility, you have to wonder why this isn't more common. The length of a left turn, between the stop line and the clearance point, rarely seems to impact left turn signalization decisions at regular intersections.

I'm trying to remember the different guidelines for allowing permissive lefts (something to Google for fun later if you're bored!), but don't recall a factor for really large intersections.  I know the intersection sight distance is based on opposing speed, which would be high in a SPUI.  So my guesses why you don't see SPUI permisssive lefts often:

1. the conflict area is so large (due to the big radius and median width) and opposing speeds are so high that drivers won't generally be able to see far enough to judge that gap.  For instance on the Nebraska example it looks like the conflict area is more than 100' from the stop line to beyond the opposing throughs.  At most SPUI I don't think you'd really have any chance to pull into the intersection due to the large radius.

2. Many SPUI are on the crest of a vertical curve.  Drivers trying to look for cars coming over a hill toward them on a tangent (fast) could lead to right angle crashes at relatively high speed - potentially serious crashes.

3.  Many SPUI don't have "positive offset" (another fun Google topic!) for the opposing lefts.  Basically someone trying to turn left the other direction will block your view of the throughs you need to yield to.

I would say another big thing is that (4) so many SPUIs are double left turns, which are protected-only by rule in most areas.

If we could find a way to fully offset the left turns, to allow traffic to pull way into the intersection while waiting (ideally, where traffic would be waiting side-by-side to turn left), and then make the left turns sharper (pull forward, harder left), we could reduce the conflict area substantially. Making the left turns lagging would also be exceptionally important, unless we want an 8-second all red.

The problem with #3 would certainly persist no matter what, with only a reduced conflict area being able to actually help that (eliminating the problem entirely being quite difficult). But luckily, at least from my experience, most overpasses are relatively level. Plus, SPUIs that are at ground-level likely have more of a valley issue, which doesn't necessarily present issues with visibility.