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Author Topic: SPUI vs DDI  (Read 20260 times)

tolbs17

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Re: SPUI vs DDI
« Reply #50 on: April 20, 2021, 09:51:36 PM »

Look at INDOT with their full cloverleafs being converted to Parclos.
Isn't that common with a lot of DOTs now; converting full cloverleafs from a freeway to arterial to some other interchange? US 40's exits to US 67, Hampton and Kingshighway in St Louis all got converted to SPUIs as part of a complete rebuild of the freeway 13 years ago. I-270's interchange with US 67 had one of the loop ramps replaced with a signal, and will be converted to a split diamond in the coming years.
But look at I-295 in Virginia.
Which point(s) on I-295? It's 53 miles long.
All of it. Most of it is cloverleafs.
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SkyPesos

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Re: SPUI vs DDI
« Reply #51 on: April 20, 2021, 09:56:08 PM »

Look at INDOT with their full cloverleafs being converted to Parclos.
Isn't that common with a lot of DOTs now; converting full cloverleafs from a freeway to arterial to some other interchange? US 40's exits to US 67, Hampton and Kingshighway in St Louis all got converted to SPUIs as part of a complete rebuild of the freeway 13 years ago. I-270's interchange with US 67 had one of the loop ramps replaced with a signal, and will be converted to a split diamond in the coming years.
But look at I-295 in Virginia.
Which point(s) on I-295? It's 53 miles long.
All of it. Most of it is cloverleafs.
Seems like Virginia have a love affair with cloverleafs in general. Found a lot of them in the NoVA area too.

tolbs17

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Re: SPUI vs DDI
« Reply #52 on: April 20, 2021, 10:05:19 PM »

Look at INDOT with their full cloverleafs being converted to Parclos.
Isn't that common with a lot of DOTs now; converting full cloverleafs from a freeway to arterial to some other interchange? US 40's exits to US 67, Hampton and Kingshighway in St Louis all got converted to SPUIs as part of a complete rebuild of the freeway 13 years ago. I-270's interchange with US 67 had one of the loop ramps replaced with a signal, and will be converted to a split diamond in the coming years.
But look at I-295 in Virginia.
Which point(s) on I-295? It's 53 miles long.
All of it. Most of it is cloverleafs.
Seems like Virginia have a love affair with cloverleafs in general. Found a lot of them in the NoVA area too.
If it was NCDOT doing that project it would have all been regular or parclos.

Btw, this one is also a standard diamond, will probably be modified to a DDI in the future.
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JoePCool14

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Re: SPUI vs DDI
« Reply #53 on: April 20, 2021, 11:39:51 PM »

Seems like Virginia have a love affair with cloverleafs in general.

Have you ever taken a trip to Illinois before by chance?
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Re: SPUI vs DDI
« Reply #54 on: April 20, 2021, 11:54:39 PM »

Seems like Virginia have a love affair with cloverleafs in general.

Have you ever taken a trip to Illinois before by chance?
Yes  :D
I had to check myself on google maps for the Chicago area interchanges, and there's way more full cloverleafs than I initially thought. I still think Virginia wins the cloverleafs count though. The Metro East area (St Louis Illinois suburbs) have a lot of whatever these interchanges are called (folded diamonds? idk).

ran4sh

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Re: SPUI vs DDI
« Reply #55 on: April 20, 2021, 11:59:35 PM »

DDIs are a lot easier to convert from a standard diamond, and they take up roughly the same footprint.

But this reason only applies to conversion to DDI from an existing interchange (specifically, it costs less because replacement of the existing bridge(s) is not required). I'm not sure if there's really a good reason to build a DDI from scratch when a SPUI is also considered.
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Re: SPUI vs DDI
« Reply #56 on: April 21, 2021, 01:18:23 AM »

The Metro East area (St Louis Illinois suburbs) have a lot of whatever these interchanges are called (folded diamonds? idk).



I would call this a folded diamond, but you could also call it a parclo AB2. I wouldn't though. I tend to only use the expression "parclo" for interchanges where loop ramps supplement the straight ramps and not replace them. But that's just me, and we all know that I have strong feelings about the names given to interchanges.
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Re: SPUI vs DDI
« Reply #57 on: April 21, 2021, 10:01:15 AM »

So, I’m going to hop into this conversation and give you this:

https://goo.gl/maps/X1amjZeW7gKUYqyD9

See, DDIs are fairly hard to screw up. The design is pretty standard, even for weird alignments. The spur though, can be various sizes, shapes and forms. THAT? That is NOT what a SPUI should look like. The whole POINT of a SPUI is to have 3 phases, Thru, Freeway On, and Freeway Off (unless it’s one of those ones where the service road has a thru movement, but with those you just add a Service Rd Thru phase). With that, coming off the freeway may be without issue, but if you’re turning onto it, we’ll, I’ll leave that as an exercise for the reader.

Honestly, though, this would be a perfect place for a DDI, no significant ramp adjustments are needed, and basically the construction would be:

Make slight adjustments to left-turn on ramps,
Close road overnight for restriping/new traffic pattern,
Install concrete islands directing traffic,
Finalize interchange.

Converting some interchanges to DDIs requires slit more work. And if MD hasn’t put in any DDIs, this could be the perfect test bed.
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BrianP

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Re: SPUI vs DDI
« Reply #58 on: April 21, 2021, 11:32:25 AM »

So, I’m going to hop into this conversation and give you this:

https://goo.gl/maps/X1amjZeW7gKUYqyD9

See, DDIs are fairly hard to screw up. The design is pretty standard, even for weird alignments. The spur though, can be various sizes, shapes and forms. THAT? That is NOT what a SPUI should look like. The whole POINT of a SPUI is to have 3 phases, Thru, Freeway On, and Freeway Off (unless it’s one of those ones where the service road has a thru movement, but with those you just add a Service Rd Thru phase). With that, coming off the freeway may be without issue, but if you’re turning onto it, we’ll, I’ll leave that as an exercise for the reader.
As far as I can tell that SPUI still uses just three phases. 
1. left turns from the ramps.
2. eastbound Allentown Rd including left turns.
3. westbound Allentown Rd including left turns.
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hbelkins

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Re: SPUI vs DDI
« Reply #59 on: April 21, 2021, 11:38:13 AM »

The Metro East area (St Louis Illinois suburbs) have a lot of whatever these interchanges are called (folded diamonds? idk).



I would call this a folded diamond, but you could also call it a parclo AB2. I wouldn't though. I tend to only use the expression "parclo" for interchanges where loop ramps supplement the straight ramps and not replace them. But that's just me, and we all know that I have strong feelings about the names given to interchanges.

Folded diamond. Typically used when there is some sort of geological feature (river) or other factor (railroad) that makes a normal diamond impractical or more expensive.
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tolbs17

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Re: SPUI vs DDI
« Reply #60 on: April 21, 2021, 12:02:00 PM »

The Metro East area (St Louis Illinois suburbs) have a lot of whatever these interchanges are called (folded diamonds? idk).



I would call this a folded diamond, but you could also call it a parclo AB2. I wouldn't though. I tend to only use the expression "parclo" for interchanges where loop ramps supplement the straight ramps and not replace them. But that's just me, and we all know that I have strong feelings about the names given to interchanges.

Folded diamond. Typically used when there is some sort of geological feature (river) or other factor (railroad) that makes a normal diamond impractical or more expensive.
Like see 264 at downing rd and black creek.
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tolbs17

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Re: SPUI vs DDI
« Reply #61 on: April 21, 2021, 12:11:06 PM »

I realized the link was the wrong coordinates. It's the interchange at I-85 and S Elm Eugene St. That interchange opened in 2004.
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SkyPesos

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Re: SPUI vs DDI
« Reply #62 on: April 21, 2021, 12:23:33 PM »

The Metro East area (St Louis Illinois suburbs) have a lot of whatever these interchanges are called (folded diamonds? idk).



I would call this a folded diamond, but you could also call it a parclo AB2. I wouldn't though. I tend to only use the expression "parclo" for interchanges where loop ramps supplement the straight ramps and not replace them. But that's just me, and we all know that I have strong feelings about the names given to interchanges.

Folded diamond. Typically used when there is some sort of geological feature (river) or other factor (railroad) that makes a normal diamond impractical or more expensive.
Like see 264 at downing rd and black creek.
I don’t see a Downing Rd or a Black Creek at either of the I-264 variants. The Louisville 264 have a folded diamond near the airport though.

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Re: SPUI vs DDI
« Reply #63 on: April 21, 2021, 12:37:10 PM »

Like see 264 at downing rd and black creek.
I don’t see a Downing Rd or a Black Creek at either of the I-264 variants. The Louisville 264 have a folded diamond near the airport though.

Given where tolbs17 lives, it might be US 264.
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Re: SPUI vs DDI
« Reply #64 on: April 21, 2021, 12:43:28 PM »

Given where tolbs17 lives ...

Pet peeve of mine.  Sorry guys, but don't post something vague and then expect me to determine where it is based on where you live.  That means I have to look at your profile (if you even have your location listed), assume you're not on vacation and posting about wherever you happen to be at the time, then break out a map and figure it out myself.  Chances are, I'm just not that interested in whatever you have to say to make it worth it.  Just include a Google Maps link and make life easier for the rest of us.  Then we might actually enter the discussion.

[/rant]
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Re: SPUI vs DDI
« Reply #65 on: April 21, 2021, 12:45:57 PM »

Given where tolbs17 lives ...

Pet peeve of mine.  Sorry guys, but don't post something vague and then expect me to determine where it is based on where you live.  That means I have to look at your profile (if you even have your location listed), assume you're not on vacation and posting about wherever you happen to be at the time, then break out a map and figure it out myself.  Chances are, I'm just not that interested in whatever you have to say to make it worth it.  Just include a Google Maps link and make life easier for the rest of us.  Then we might actually enter the discussion.

[/rant]
Agreed.

I looked, it's US-264 near Wilson, NC.

Black Creek - https://www.google.com/maps/@35.674038,-77.9062037,939m/data=!3m1!1e3
Downing Rd - https://www.google.com/maps/@35.6958441,-77.9748382,1183m/data=!3m1!1e3
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tolbs17

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Re: SPUI vs DDI
« Reply #66 on: April 21, 2021, 03:11:41 PM »

Given where tolbs17 lives ...

Pet peeve of mine.  Sorry guys, but don't post something vague and then expect me to determine where it is based on where you live.  That means I have to look at your profile (if you even have your location listed), assume you're not on vacation and posting about wherever you happen to be at the time, then break out a map and figure it out myself.  Chances are, I'm just not that interested in whatever you have to say to make it worth it.  Just include a Google Maps link and make life easier for the rest of us.  Then we might actually enter the discussion.

[/rant]
I was at work and was using my phone...
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kphoger

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Re: SPUI vs DDI
« Reply #67 on: April 21, 2021, 03:22:17 PM »

I was at work and was using my phone...

Then give context, like a town name or something.

Don't just throw out "264 at downing rd and black creek" in reply to a post whose only geographical context was metro Saint Louis, then expect us to know you're talking about Wilson County, NC.
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Re: SPUI vs DDI
« Reply #68 on: April 21, 2021, 11:56:29 PM »

Given where tolbs17 lives ...

Pet peeve of mine.  Sorry guys, but don't post something vague and then expect me to determine where it is based on where you live.  That means I have to look at your profile (if you even have your location listed), assume you're not on vacation and posting about wherever you happen to be at the time, then break out a map and figure it out myself.  Chances are, I'm just not that interested in whatever you have to say to make it worth it.  Just include a Google Maps link and make life easier for the rest of us.  Then we might actually enter the discussion.

[/rant]

Thanks for saying that.   :clap:   Without context it would be reasonable to assume I-264 rather than US 264.

tolbs17

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Re: SPUI vs DDI
« Reply #69 on: July 24, 2021, 04:31:30 PM »

How is a Parclo A4/B4 better than a DDI and SPUI?
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jeffandnicole

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Re: SPUI vs DDI
« Reply #70 on: July 24, 2021, 04:47:49 PM »

How is a Parclo A4/B4 better than a DDI and SPUI?

There's never one blanket answer. An interchange design is chosen based on traffic, roadway feature, volume, etc
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Re: SPUI vs DDI
« Reply #71 on: July 24, 2021, 10:22:47 PM »

True. But if I were to give a blanket answer anyways:

* parclos have fewer conflict points than SPUIs or DDIs;
* parclos are more easily implemented along signalized corridors as they have very simple phasing;
* parclos allow for non-signalized operation (B4 in particular); the vast majority of SPUIs and DDIs are signalized (maybe all but a handful) (unsignalized B4, unsignalized A4).

My general preference is for B4 parclos over A4 parclos; B4's have left turns, which are harder to implement on existing, potentially narrow bridges, but are simpler to operate than the A4's left turns that require both directions to stop. Additionally, the B4 has better traffic distribution (traffic turning left stays left, traffic turning right stays right) compared to A4s which have all movements on the right-most lanes (sometimes better, to be fair).

SkyPesos

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Re: SPUI vs DDI
« Reply #72 on: July 24, 2021, 10:32:20 PM »

My general preference is for B4 parclos over A4 parclos; B4's have left turns, which are harder to implement on existing, potentially narrow bridges, but are simpler to operate than the A4's left turns that require both directions to stop. Additionally, the B4 has better traffic distribution (traffic turning left stays left, traffic turning right stays right) compared to A4s which have all movements on the right-most lanes (sometimes better, to be fair).
Huh, so you prefer the less common one of the two. I don't think I've ever seen a B4 parclo, almost always A4.

tolbs17

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Re: SPUI vs DDI
« Reply #73 on: July 25, 2021, 12:36:25 AM »

The advantages of SPUIs compared to other interchanges is when turning left, it's easier for big vehicles such as trucks, buses, and RVs to turn easier without making a wider turn.

And the next advantage is that of where you stop, is only in one junction. No need to stop twice compared to the other interchanges.

NCDOT still builds SPUIs, like the one at I-295 and US-401 in Western Fayetteville, although they consider it more if the highway is going over the arterial. Although in general it's more expensive. That's just a fact.
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Re: SPUI vs DDI
« Reply #74 on: July 25, 2021, 01:57:51 AM »

My general preference is for B4 parclos over A4 parclos; B4's have left turns, which are harder to implement on existing, potentially narrow bridges, but are simpler to operate than the A4's left turns that require both directions to stop. Additionally, the B4 has better traffic distribution (traffic turning left stays left, traffic turning right stays right) compared to A4s which have all movements on the right-most lanes (sometimes better, to be fair).
Huh, so you prefer the less common one of the two. I don't think I've ever seen a B4 parclo, almost always A4.

I've heard the A4 is preferred because of concerns around tip-over with the B4 off-ramp using a loop, but I've always considered that an old wives tale.

I live very close to a B4 parclo here in Tacoma, converted from an old cloverleaf. It flows ridiculously well, and I have never seen anything tip over using the loop. I did some extensive Googling and can't find evidence of it occurring either.

 


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