Strange Interchanges

[SkyPesos]

In suburban Cincinnati, I-75 SB exit to Lockland (Exit 12) is nearly a 90 degree right turn.

Also no fixed gore (which is definitely below interstate standards), so some driver could theoretically blow past by on the through movement using the exit only lane. Looking at GSV, it looks like a few people done that already, judging by the skid marks in the gore.

Though this interchange will be removed as part of a future phase of the "Through the Valley" project.

[jakeroot]

^ You're seeing things.  Exit 2 (I-91/VT 9) was built in its present configuration from the get-go.  Here is a photograph showing an aerial view of the interchange from 1962, a couple years after it opened

Whatever I'm seeing is visible from multiple angles.

I'm aware of what you're seeing at that location.  Especially on the southbound side, I can see what one might perceive as flat grading.  But I'm pointing out again that the current interchange configuration is what was built from the get-go.

But then why start off with, "you're seeing things", a phrase reserved for when you're alluding to someone imagining something that doesn't exist? The grading (ramp or no ramp) clearly exists.

[froggie]

^ Because they saw what he thought was a half-diamond in that grading.  I can understand where one would come to that conclusion but that is definitely not the case here.  Though in fairness, I'm more familiar with that interchange than most forum members.

[vtk]

Yes, I don't dispute the historical record here. I'm just confused as to why the embankments are that way. Also, I don't use he/him pronouns anymore.

[froggie]

^ Missed that.  Apologies.

Could not tell you why the embankments are that way.  While there's a number of I-91 construction photos now online thanks to UVM (University of Vermont), I have yet to find any for that particular interchange.  Just some aerial images from a couple years after opening.

[webny99]

Not sure if this fits the thread, but I'm fascinated by this overlapping DDI/SPUI in Marion, IL. I've never seen two interchanges overlapping like this without any access from one set of ramps to the other, much less with these two relatively new designs.

[froggie]

I'd say it fits.

Worth noting some history there...originally, I-57/IL 13 was a standard cloverleaf and The Hill Ave did not exist over 57.  The Hill Ave was built over 57 ca. 2008 along with a single southbound off-ramp.  The northbound on-ramp from The Hill was added ca. 2011.  57/13 was converted into a SPUI (along with ramps to/from the south at The Hill and widening 57 through Marion) ca. 2012-14, while The Hill was converted from a standard diamond to a DDI in 2015.

[7/8]

One I just noticed now is the 401 at Hurontario St in Mississauga, ON (Google Maps). Exiting EB, the off-ramp splits in two, with a choice of going to Hurontario or Whittle Street. The Whittle Street off-ramp requires two overpasses and simply leads to a small street one block east of Hurontario. Also, the off-ramp for Whittle starts as one-lane, goes up to two-lanes, then goes back down to one-lane before the roundabout at the north end of the Whittle. I'm surprised this off-ramp was built at all, let alone with two-lanes.

[MCRoads]

Not sure if this fits the thread, but I'm fascinated by this overlapping DDI/SPUI in Marion, IL. I've never seen two interchanges overlapping like this without any access from one set of ramps to the other, much less with these two relatively new designs.

I just found that the other day, but wasn't sure where to put it here. You also missed the roundabout on the DDI road. Progressive DOT!

Interchanges can often be close enough that although they may both be necessary, it is not necessary to give access between the ramps. Look at Lindsay St and OK-9 (I-35 exits 208 A/B) in Norman.

[thspfc]

Not sure if this fits the thread, but I'm fascinated by this overlapping DDI/SPUI in Marion, IL. I've never seen two interchanges overlapping like this without any access from one set of ramps to the other, much less with these two relatively new designs.

That reminds me of this configuration in Wausau, WI: https://www.google.com/maps/@44.9568438,-89.6671109,15.4z

If you ignore the larger WI-29 interchange, it's pretty similar, except there's a half diamond interchange at the lesser road (Sherman), compared to the full DDI at The Hill Ave. I think the one full interchange and one half interchange approach makes more sense. It causes less weaving and costs less.

[webny99]

I'd say it fits.

Worth noting some history there...originally, I-57/IL 13 was a standard cloverleaf and The Hill Ave did not exist over 57.  The Hill Ave was built over 57 ca. 2008 along with a single southbound off-ramp.  The northbound on-ramp from The Hill was added ca. 2011.  57/13 was converted into a SPUI (along with ramps to/from the south at The Hill and widening 57 through Marion) ca. 2012-14, while The Hill was converted from a standard diamond to a DDI in 2015.

Interesting. That's nearly a decade of changes to get to the current configuration! You can tell from satellite view that I-57/IL 13 used to be a cloverleaf. The cloverleaf could have theoretically been left intact even with The Hill Ave interchange; so it's interesting that it was still changed to a SPUI. Perhaps to avoid confusion with a new interchange in close proximity, or if volumes simply didn't warrant a cloverleaf? Or maybe some combination of both.

[webny99]

Interchanges can often be close enough that although they may both be necessary, it is not necessary to give access between the ramps. Look at Lindsay St and OK-9 (I-35 exits 208 A/B) in Norman.

That's true, although in that case, 28th Ave. SW is essentially part of the interchange and serves the same purpose as connecting ramps. The Marion example is a little different because you have to go close to 1/2 mile in either direction (to either Halfway Rd or N Carbon St.) to get between IL 13 and The Hill Ave.

[webny99]

That reminds me of this configuration in Wausau, WI: https://www.google.com/maps/@44.9568438,-89.6671109,15.4z

If you ignore the larger WI-29 interchange, it's pretty similar, except there's a half diamond interchange at the lesser road (Sherman), compared to the full DDI at The Hill Ave. I think the one full interchange and one half interchange approach makes more sense. It causes less weaving and costs less.

Similar to the above, in this case WI 29 has its own set of ramps to WI 52, which serves the same purpose as the connecting ramps would.

Speaking more generally, in cases with two closely spaced interchanges the most cost-effective solution would be a half-diamond in each location for just four ramps total. Of course, you'd also need a service road or very good connectivity between the two local streets, so I'm not sure if it would work at this particular location or the Marion location, but there is certainly precedent: I-390 at NY 15/NY 251, NY 5 at Hinsdale Rd/Bennett Rd, QEW at Christie St/Ontario St/Maple St.

For a counter-example, where poor local street connectivity makes this design less desirable and borderline dysfunctional, I-81 in Pulaski, NY. This one definitely needs to be two full interchanges; getting off at Pulaski for fuel/services and getting back on requires an absurd six turns over nearly 3 miles.

[webny99]

One I just noticed now is the 401 at Hurontario St in Mississauga, ON (Google Maps). Exiting EB, the off-ramp splits in two, with a choice of going to Hurontario or Whittle Street. The Whittle Street off-ramp requires two overpasses and simply leads to a small street one block east of Hurontario. Also, the off-ramp for Whittle starts as one-lane, goes up to two-lanes, then goes back down to one-lane before the roundabout at the north end of the Whittle. I'm surprised this off-ramp was built at all, let alone with two-lanes.

Interesting concept! It certainly makes it easier for freeway traffic to access the commercial development on Britannia Ave, as it avoids the right turn, weave, and subsequent left turn. I am intrigued by the second lane though; I can't imagine it's really warranted and the fact that it ends before the roundabout means that it's essentially a passing lane. Can't say I've ever seen something like that for a freeway ramp before.

[Rothman]

For a counter-example, where poor local street connectivity makes this design less desirable and borderline dysfunctional, I-81 in Pulaski, NY. This one definitely needs to be two full interchanges; getting off at Pulaski for fuel/services and getting back on requires an absurd six turns over nearly 3 miles.

Such upgrades would be such a low priority that it brings to mind one of Space Ghost's interviews:

Nobody cares, Moby.  Nobody.

[webny99]

For a counter-example, where poor local street connectivity makes this design less desirable and borderline dysfunctional, I-81 in Pulaski, NY. This one definitely needs to be two full interchanges; getting off at Pulaski for fuel/services and getting back on requires an absurd six turns over nearly 3 miles.

Such upgrades would be such a low priority that it brings to mind one of Space Ghost's interviews:

Nobody cares, Moby.  Nobody.

Only because it's the middle of nowhere. Throw that configuration in a city or suburb and it would be a nightmare.

[Rothman]

For a counter-example, where poor local street connectivity makes this design less desirable and borderline dysfunctional, I-81 in Pulaski, NY. This one definitely needs to be two full interchanges; getting off at Pulaski for fuel/services and getting back on requires an absurd six turns over nearly 3 miles.

Such upgrades would be such a low priority that it brings to mind one of Space Ghost's interviews:

Nobody cares, Moby.  Nobody.

Only because it's the middle of nowhere. Throw that configuration in a city or suburb and it would be a nightmare.

Let me know when you come back from Fantasyland. ;D

[vdeane]

Stuff like I-81 in Pulaski is why I don't like getting off the interstate without planning in advance.  That gap is so large that both directions might not even have the same exit number when I-81 goes mile-based (unless they decide to fudge one of the directions).

[ran4sh]

That should in no way be treated as a single interchange. In other words, the exit numbers should be different even without converting to mile-based.

[DJStephens]

Believe that is what A - B - C suffixes are for.  Have no idea if that is standard.   

[J N Winkler]

My fix for the I-81/Pulaski situation, which is basically a split diamond with no direct connection between the two halves, would be simply to place "No Re-entry In Same Direction" signs (for which a standard design exists in Ohio and possibly other states) on the approach to both exit ramps.

Was this segment of I-81 built fairly early in the era of first Interstate construction?  There is a similar succession of restricted-access interchanges a bit further north in Lacona.

[webny99]

My fix for the I-81/Pulaski situation, which is basically a split diamond with no direct connection between the two halves, would be simply to place "No Re-entry In Same Direction" signs (for which a standard design exists in Ohio and possibly other states) on the approach to both exit ramps.

Certainly agreed. I've seen variations of this type of signage in Pennsylvania and Maryland, but to my knowledge no variations of this are used in New York. NYSDOT seems to prefer supplementary "TO I-81" banners, and in fairness, these do appear at both half-diamond interchanges and at the intersections in between, such that anyone who exits and wishes to re-enter would theoretically be able to follow signage to do so. IMO it's not an excuse not to inform drivers before they exit, but I suspect it to be NYSDOT's reasoning nonetheless.

Was this segment of I-81 built fairly early in the era of first Interstate construction?  There is a similar succession of restricted-access interchanges a bit further north in Lacona.

The first sections of I-81 north of Syracuse opened in the late 1950's, but both the Pulaski and Lacona interchanges appear to be part of the section that opened in 1961, at least according to Wikipedia.

[vdeane]

My fix for the I-81/Pulaski situation, which is basically a split diamond with no direct connection between the two halves, would be simply to place "No Re-entry In Same Direction" signs (for which a standard design exists in Ohio and possibly other states) on the approach to both exit ramps.

Certainly agreed. I've seen variations of this type of signage in Pennsylvania and Maryland, but to my knowledge no variations of this are used in New York.

Oddly enough, such signage used to be used on I-88 but no longer is.  There's also this odd exit.

[webny99]

There's also this odd exit.

Which, to bring things full circle, happens to be a pretty good candidate for this thread! 

I've never understood why that one ramp exists without any counterpart whatsoever. At least a southbound entrance ramp would be nice, and you could probably make the case for a full interchange, especially if there was better access to the development south of Mud Creek.

[Rothman]

There's also this odd exit.

Which, to bring things full circle, happens to be a pretty good candidate for this thread! 

I've never understood why that one ramp exists without any counterpart whatsoever. At least a southbound entrance ramp would be nice, and you could probably make the case for a full interchange, especially if there was better access to the development south of Mud Creek.

I would have thought vdeane would have recognized one of the largest wetland areas in the region...

Oddly enough, the one-ramper was just discussed at SMTC.  Never going to be a full interchange due to the gigantic wetland issue.