"Why?" interchange designs

[kphoger]

I hope this hasn't been brought up before, but can anyone tell me the backstory on this part of this sorta-cloverleaf:  https://goo.gl/maps/CX8UkxyMQvukizVE7

Really what I'm wondering is, why does the ramp from EB Southern State Parkway to SB CR 13/Fifth Avenue need a ramp leading back to EB Southern State Parkway and a slip lane to the ramp that you're already on?  It also does the same thing from the WB direction. 

Looks like those ramps doubled/double as rest stops?  If so, then the slips are for resting traffic to get back on the highway.  Just a guess.

[Ned Weasel]

Looks like those ramps doubled/double as rest stops?  If so, then the slips are for resting traffic to get back on the highway.  Just a guess.

Good observation!  I suppose those come in handy when you need a payphone and/or a trash can.

[dfilpus]

I hope this hasn't been brought up before, but can anyone tell me the backstory on this part of this sorta-cloverleaf:  https://goo.gl/maps/CX8UkxyMQvukizVE7

Really what I'm wondering is, why does the ramp from EB Southern State Parkway to SB CR 13/Fifth Avenue need a ramp leading back to EB Southern State Parkway and a slip lane to the ramp that you're already on?  It also does the same thing from the WB direction. 

In Streetview, it looks like there have been bus stops on the ramps between the exit ramps and the entrance ramps.

[ErmineNotyours]

The interchange between WA-18 and WA-167 in Auburn is not bad. It works for the traffic it handles.

However, I would personally give it a "why?" stamp because although it takes a ton of land, it's still missing several maneuvers such as northbound to westbound and eastbound to southbound. Arguably the least important maneuvers but, with this much land, how did they not find a way to fit it in? Well...

WA-18 came first, alongside the interchange with West Valley Hwy. These were built around 1960. The full interchange with WA-167 came with its construction in the 1970s (then and still known as the Valley Fwy). Rather than rebuild the WA-18/West Valley Hwy interchange to free up room, it was decided to basically not touch it. That still left the state with plenty of ROW, but it doesn't seem to have been utilized all that well. Even looking at the existing movements, some of them are very unsafe (tight exits, tight merges, short weaves, weirdly shaped loop). Yet, again, so much ROW here to do something so much better.

So, to put it plainly: it's not that there isn't an explanation for why there are missing maneuvers. But WSDOT (or the preceding highway department) went the cheap route for the new interchange, and we're left today with a substandard design that takes tons of land and yet still has missing maneuvers. Brilliant.

I noticed in my 1977 Thomas Bros map that they falsely show the interchange built out with flyovers.

[jakeroot]

I noticed in my 1977 Thomas Bros map that they falsely show the interchange built out with flyovers.

Gotta wonder if that was someone drawing with an inspired mind, or if there were genuinely plans for a better interchange there.

At any rate, this is easily the first and only 'IRL' reference to any flyovers at 18/Valley Fwy interchange that I have ever seen. So, yeah, amazing find.

[SkyPesos]

I noticed in my 1977 Thomas Bros map that they falsely show the interchange built out with flyovers.

Gotta wonder if that was someone drawing with an inspired mind, or if there were genuinely plans for a better interchange there.

At any rate, this is easily the first and only 'IRL' reference to any flyovers at 18/Valley Fwy interchange that I have ever seen. So, yeah, amazing find.

If that's in the same land area as the current interchange, that's impressive if I say so myself, considering the existing interchange is missing two ramp movements while this one got it all.

[US 89]

I would love to know the story behind the interchange at Paseo del Norte (NM 423) and 2nd St in Albuquerque. It’s basically a SPUI, but with left exits and right entrances.

I have never seen this design anywhere else. Seems like those left exits would make it more dangerous while providing no real benefit otherwise.

[jakeroot]

I noticed in my 1977 Thomas Bros map that they falsely show the interchange built out with flyovers.

Gotta wonder if that was someone drawing with an inspired mind, or if there were genuinely plans for a better interchange there.

At any rate, this is easily the first and only 'IRL' reference to any flyovers at 18/Valley Fwy interchange that I have ever seen. So, yeah, amazing find.

If that's in the same land area as the current interchange, that's impressive if I say so myself, considering the existing interchange is missing two ramp movements while this one got it all.

To be fair, the design shown above almost totally eliminates the interchange with West Valley Hwy (shown on the map as both "60th Ave S" and WA-181), which frees up a substantial amount of room on the west side of the interchange. That interchange, which is vintage early-1960s, was decided to be kept basically in its entirety when the Valley Fwy was pushed through in the 70s. That made flyovers and full connections very difficult, as there was very little room for additional ramps on the west side of the interchange. There would have been ways to figure it out, sure, but I guess they decided it wasn't worth it.

For my redesign last April, which actually puts the flyovers in the opposing corners (they also propose an additional sweeping ramp EB to SB that goes below-grade), I eliminated said interchange's movements to/from the east to free up land area and allow proper ramps. They have gone to the extreme in this map and simply eliminated all movements between the freeways and West Valley Hwy, apart from a singular westbound off-ramp.

[webny99]

I would love to know the story behind the interchange at Paseo del Norte (NM 423) and 2nd St in Albuquerque. It's basically a SPUI, but with left exits and right entrances.

I have never seen this design anywhere else. Seems like those left exits would make it more dangerous while providing no real benefit otherwise.

Interesting case -- was this interchange originally constructed like this, or did it have a different design previously?

I can't say I've ever seen a SPUI underneath the freeway; they're almost always on an overpass for obvious visibility reasons. So if there was some reason why Paseo Del Norte Blvd needed to have the overpass (or if that's how it was designed previously), the wide median with the SPUI in the middle makes at least some degree of sense.

[SkyPesos]

I would love to know the story behind the interchange at Paseo del Norte (NM 423) and 2nd St in Albuquerque. It's basically a SPUI, but with left exits and right entrances.

I have never seen this design anywhere else. Seems like those left exits would make it more dangerous while providing no real benefit otherwise.

Here's an example like that one at I-170 and MO 180 with the wide median, though the exit ramps are on the right.

I can't say I've ever seen a SPUI underneath the freeway; they're almost always on an overpass for obvious visibility reasons.

Take a look at I-15 in the SLC area on GSV. I counted 8 under SPUIs in a row (excluding the I-215 interchange) between 12300 South and the southern I-80 interchange. Compared to some other ones I've been on (*cough* I-64 and US 67), the off-ramp left turn signals have great visibility, as they're placed on the overpass.

[US 89]

I would love to know the story behind the interchange at Paseo del Norte (NM 423) and 2nd St in Albuquerque. It’s basically a SPUI, but with left exits and right entrances.

I have never seen this design anywhere else. Seems like those left exits would make it more dangerous while providing no real benefit otherwise.

Interesting case -- was this interchange originally constructed like this, or did it have a different design previously?

I can't say I've ever seen a SPUI underneath the freeway; they're almost always on an overpass for obvious visibility reasons. So if there was some reason why Paseo Del Norte Blvd needed to have the overpass (or if that's how it was designed previously), the wide median with the SPUI in the middle makes at least some degree of sense.

The Albuquerque interchange was built in that configuration in the mid-1990s. Before then it was an at-grade intersection.

And to SkyPesos's point about the SPUIs in the Salt Lake area - by my count, Utah currently has 38 SPUIs, and 27 of them have the freeway over the interchange which seems to be the default for new construction. In fact, with the ongoing Bangerter Highway interchange upgrades in the southwest Salt Lake Valley, at least two proposed interchanges were initially planned as freeway-over SPUIs but were changed to freeway-under after the public comment period.

[webny99]

SPUI's are non-existent in this area, which is probably why I'm not used to seeing them under the freeway. It seems like a disaster waiting to happen for first-time users.

[US 89]

SPUI's are non-existent in this area, which is probably why I'm not used to seeing them under the freeway. It seems like a disaster waiting to happen for first-time users.

Eh, I've never seen anybody have issues with any of ours. Especially compared with some of the unconventional designs around here like DDIs and CFIs, SPUIs of any sort seem very intuitive.

One advantage of a freeway-over configuration is that it's rather difficult to plow a SPUI when it snows because there's such a large pavement area - but this is obviously less of an issue if you have the freeway over the interchange. This is not as much of an issue in areas where it doesn't snow a lot, but both Utah and New York get enough regular snowstorms in winter that I'd imagine this factors into the analysis in some way.

[jakeroot]

It seems like a disaster waiting to happen for first-time users.

SPUIs in general, or having them below a freeway?

Either way, I have no idea what you're talking about. SPUIs are not usually disasters, no matter how you look at them. I'm not a fan because the intersections are gigantic, so there's tons of redundant space. But safety-wise, there doesn't seem to be any outstanding issues with them.

[kphoger]

As long as you don't stick something on the pavement in the middle of the SPUI, because it gets hidden by shadows all the time and is likely to get run down.

This works.
This keeps getting knocked down.

[johndoe]

I would love to know the story behind the interchange at Paseo del Norte (NM 423) and 2nd St in Albuquerque. It's basically a SPUI, but with left exits and right entrances.

I have never seen this design anywhere else. Seems like those left exits would make it more dangerous while providing no real benefit otherwise.

So historic aerials shows in 1991 this was an at-grade intersection.  Also...pan to the east and check out the railroad tracks still in place! https://goo.gl/maps/coZbQQJAEQa7Jw6U7  Even farther east, the intersection of Jefferson St was still at-grade in 2011.  So that "freeway" is an interesting one!

My guess is that the big reason is that they wanted to keep the bridge spans (distance between support piers) as short as possible (to have a "thinner" bridge and less earthwork).  See how there are supports between the main roadway and the left turns onto the freeway?  That means the bridge doesn't need to be so tall / expensive.  A lot of "SPUI under" have REALLY long spans since the lanes from the left turns get in the way.  I also bet the version we see today had smaller construction impacts than raising the freeway exactly where the intersection is.  They were able to leave the intersection and build the new portions of freeway outside without disrupting traffic.

[ztonyg]

I would love to know the story behind the interchange at Paseo del Norte (NM 423) and 2nd St in Albuquerque. It’s basically a SPUI, but with left exits and right entrances.

I have never seen this design anywhere else. Seems like those left exits would make it more dangerous while providing no real benefit otherwise.

Interesting case -- was this interchange originally constructed like this, or did it have a different design previously?

I can't say I've ever seen a SPUI underneath the freeway; they're almost always on an overpass for obvious visibility reasons. So if there was some reason why Paseo Del Norte Blvd needed to have the overpass (or if that's how it was designed previously), the wide median with the SPUI in the middle makes at least some degree of sense.

Arizona has several SPUIs under freeways. Off the top of my head I can think of Loop 202 / Rural Rd, Loop 101 / Frank Lloyd Wright Blvd, Loop 101 / Cave Creek Rd, Loop 101 / Bell Road (Glendale), AZ 143 / University Drive, AZ 143 / Washington Street, Loop 202 / 24th Street, Loop 202 / 32nd Street, AZ 51 / McDowell Rd, AZ 51 / Thomas Rd, AZ 51 / Indian School Rd.

Also I-94 / Telegraph Rd in Michigan (with the football shaped bridge) is an SPUI underneath a freeway.

[ilpt4u]

The Southern Illinois SPUI, IL 13 @ I-57 in Marion, is a Freeway Over

As long as you don't stick something on the pavement in the middle of the SPUI, because it gets hidden by shadows all the time and is likely to get run down.

This works.
This keeps getting knocked down.

Of course, IDOT D9 has the I-57 shield on an island in the middle of the intersection under Freeway/in the shadows
https://goo.gl/maps/Zoh7aFUtoSRou5Pw7

[webny99]

It seems like a disaster waiting to happen for first-time users.

SPUIs in general, or having them below a freeway?

Having them below a freeway. It seems like it's a lot more common that I thought, which is partly because most of the examples I've seen on the forum and elsewhere have been overpasses, and partly because, again, SPUI's are literally non-existent in NY/NJ/PA, so I'm kind of flying blind here.

[SkyPesos]

It seems like a disaster waiting to happen for first-time users.

SPUIs in general, or having them below a freeway?

Having them below a freeway. It seems like it's a lot more common that I thought, which is partly because most of the examples I've seen on the forum and elsewhere have been overpasses, and partly because, again, SPUI's are literally non-existent in NY/NJ/PA, so I'm kind of flying blind here.

Here's one NY example of an under SPUI: I-278 and Northern Blvd. Also includes the "signs island"  in the middle.

[vdeane]

It seems like a disaster waiting to happen for first-time users.

SPUIs in general, or having them below a freeway?

Having them below a freeway. It seems like it's a lot more common that I thought, which is partly because most of the examples I've seen on the forum and elsewhere have been overpasses, and partly because, again, SPUI's are literally non-existent in NY/NJ/PA, so I'm kind of flying blind here.

I commute on a SPUI every day.*

*Well, every day I have a commute, due to the pandemic, but you get the idea.

[froggie]

Either way, I have no idea what you're talking about. SPUIs are not usually disasters, no matter how you look at them. I'm not a fan because the intersections are gigantic, so there's tons of redundant space. But safety-wise, there doesn't seem to be any outstanding issues with them.

For most SPUIs, no.  But for those located in cities with high bicycle/pedestrian traffic, there's at least one documented location (MN 55/Lake St in Minneapolis, MN) with a high level of safety issues for non-motorized modes transiting the interchange.

[webny99]

... partly because, again, SPUI's are literally non-existent in NY/NJ/PA, so I'm kind of flying blind here.

I commute on a SPUI every day.*

That's one of how many in the entire state... two? three?

[jeffandnicole]

SPUI's are non-existent in this area, which is probably why I'm not used to seeing them under the freeway. It seems like a disaster waiting to happen for first-time users.

Then the accident rate would be thru the roof every time a new driver encounters one.

A SPUI is nothing more than a common left turn. At a typical intersection, opposing directions make simultaneous left turns all day long.

[SkyPesos]

... partly because, again, SPUI's are literally non-existent in NY/NJ/PA, so I'm kind of flying blind here.

I commute on a SPUI every day.*

That's one of how many in the entire state... two? three?

In addition to what I noted for NY above, at least two.