Why are states downgrading interchnges?

[NE2]

That's a B6, because it has six ramps.  A B4 has only four ramps:

No, a B2 has four ramps.
https://www.aaroads.com/forum/index.php?topic=8127

[vtk]

That's a B6, because it has six ramps.  A B4 has only four ramps:

No, a B2 has four ramps.
https://www.aaroads.com/forum/index.php?topic=8127

I must have misremembered something.  Point conceded.

[hbelkins]

The US 71 & US 59 and I-30 interchange in Texarkana was a cloverleaf turned into a diamond, but a downgrade I would exactly not say so.  All they did was eliminate the weaving that originally existed. 

Now if you look at it for the signal aspect, it may be a downgrade cause you now have to wait at a signal instead of free flowing as you were for some time before.  However, signals are being erected all throughout many states at typical intersections where for years we flowed smoothly and now have to stop for a minuet or two along our travel paths.  So this is basically no different than that.

I would guess that the development of I-49 as a through route will take a lot of traffic out of that interchange.

Actually, I don't have any problems with them. What do you dislike about them?

I don't hate SPUIs, and I do think they're really good for replacing diamonds in tight spaces with high traffic counts. It's also really fun to zip across all those lanes once the light turns green when you're exiting and turning left. No second intersection!

But they're called Single Point Urban Interchanges. In urban areas, they're great. Where there's more space, I (like Tradephoric) would prefer a parclo.

The new interchange between the Natcher Parkway extension and Plano Road (KY 622) in Bowling Green, Ky., was built as a SPUI. It is right in the middle of what formerly was a corn field. I don't know if it was built in anticipation of development in that area or what, but I was surprised to see a SPUI in the middle of nowhere.

[tradephoric]

It isn't surprising they chose the parclo A4 as that seems to be the preferred type of parclo.  Compare the time-distance diagram along US-40 for each type of parclo.




With a parclo B4 you can maintain good dual progression between High School Road and Morris Street as the ramp signals only stop one direction of travel (and can be easily coordinated to the upstream signal).  With the parclo A4, the ramp signals stop both directions of travel and good progression deteriorates in at least one direction of travel. 

[txstateends]

Now if you look at it for the signal aspect, it may be a downgrade cause you now have to wait at a signal instead of free flowing as you were for some time before.  However, signals are being erected all throughout many states at typical intersections where for years we flowed smoothly and now have to stop for a minuet or two along our travel paths.  So this is basically no different than that.

Parclo B4 in Dallas, Texas:

Ah yes, the current arrangement at US 75/Loop 12-Northwest Hwy. in Dallas.  It was originally built as a full cloverleaf but was changed when US 75 was redone 1989-1999.  I remember how surprised I was when it was changed, but I've come to accept it.

[Alps]

US 1 & 9 and NJ 35 in Woodbridge was converted to a diamond from its original cloverleaf form, however I think that had to do with weaving issues.

It had to do with outdated interchange design - very tight loops, and NJ 35 briefly acted like a freeway between traffic lights - cars would speed up, hit the wider road in the underpass, and try to pass someone before the road narrowed again. Very dangerous in the case of NJ driving. Also keep in mind that the interchange was built in 1929, back when this was US 1 over US 9, the two most important north-south routes in the state. Now there's the Parkway and Turnpike, and the road underneath is just NJ 35, with US 9 also rerouted. There hasn't been a need for a cloverleaf here in at least 60 years.

[Crazy Volvo Guy]

Getting rid of weaving movements is a Good Thing.

This, times a billion.  Nothing frustrates me more than weave lanes when driving a vehicle that is 73 feet long and slow to accelerate and brake.  Even when I'm not actually using that weave lane.

[Duke87]

As has been hinted at, I think in most cases it's likely a result of progress in roadway design. There was a time when trying to provide a lot of free-flowing movements was considered cool, with out regards to the effects it had other than that it sped traffic up. A lot of old junctions involved tight loops, weaving, or some other design aspect that is in the modern day known to have a negative impact on safety. Since fixing the safety issue while keeping the interchange as "powerful" as it currently is is often not worth the cost and/or not possible given space constraints, "downgrading" the interchange often becomes the preferred alternative - because the interchange still does its job (albeit perhaps it causes some people to have to wait an extra 30 seconds), but it increases safety.

And in some cases (see the US 1&9/NJ 35 example), even from a traffic flow perspective the "downgrade" is an obvious improvement. Yes, the new interchange has a signal where the old one didn't. But it also has acceleration lanes, rather than blind curves ending at yield signs.

[lepidopteran]

Near Columbus, OH, the (northern) interchange between arterial US-23 and I-270 is currently a full cloverleaf.  A plan is underway remove two of the loops and make a signalized parclo.

http://www.dot.state.oh.us/projects/I-270/23/Pages/default.aspx

[vtk]

Near Columbus, OH, the (northern) interchange between arterial US-23 and I-270 is currently a full cloverleaf.  A plan is underway remove two of the loops and make a signalized parclo.

http://www.dot.state.oh.us/projects/I-270/23/Pages/default.aspx

Weaving is a big problem there currently.

[Brian556]

The  US 60/ BUS I-40 (OLD US 66) Amarillo, Tx was downgraded to an intersection, due to traffic volumes declining due to I-40 being built.

https://maps.google.com/?ll=35.252348,-101.645744&spn=0.012406,0.024912&t=h&z=16

Also, in Dallas, there was a flyover NB SH 310 (OLD US 75) at Illinois Av (FMR SH 246). It's now a flat intersection.

https://maps.google.com/?ll=32.711433,-96.75391&spn=0.006391,0.012456&t=h&z=17

[lepidopteran]

In Miami Beach, FL, there used to be a single flyover ramp from W. 63rd St. to NB A1A (Indian Creek Dr. along the Intracoastal, as opposed to Collins Ave. along the beach which at that point is NB only.)  The structure was all concrete IIRC, and was held up by sleek V-like piers.  Since the ramp was one-movement-only, there were flashing red lights at the ramp's exit on A1A.  Not completely sure why it was demolished, but I suspect that maintenance issues were at least partly to blame.  Anyone know for sure?

[NE2]

In Miami Beach, FL, there used to be a single flyover ramp from W. 63rd St. to NB A1A (Indian Creek Dr. along the Intracoastal, as opposed to Collins Ave. along the beach which at that point is NB only.)  The structure was all concrete IIRC, and was held up by sleek V-like piers.  Since the ramp was one-movement-only, there were flashing red lights at the ramp's exit on A1A.  Not completely sure why it was demolished, but I suspect that maintenance issues were at least partly to blame.  Anyone know for sure?

It seems to have been a combination of outdated design (including low clearance underneath) and locals' desire to tear it down to piss off CP Zilliacus.