SPUI vs DDI

[tolbs17]

A disadvantage of a SPUI interchange is that you cannot make a U-turn going in the opposite direction compared to the other interchanges.

I though SPUIs are one of the easier interchanges to make a U-turn.

I was thinking that too!

If this interchange was constructed today, it would have been a DDI I'm sure.

[tolbs17]

SPUIs and Parclo B4s are more appropriate for main highways.

DDIs and Dumbbells (and dogbones) are for small arterials.

[SkyPesos]

SPUIs and Parclo B4s are more appropriate for main highways.

DDIs and Dumbbells (and dogbones) are for small arterials.

Not even small arterials for DDIs. Major arterials with tons of traffic entering or exiting the freeway compared to staying on the arterial could warrant a DDI over a SPUI.

[ztonyg]

SPUIs and Parclo B4s are more appropriate for main highways.

DDIs and Dumbbells (and dogbones) are for small arterials.

Not even small arterials for DDIs. Major arterials with tons of traffic entering or exiting the freeway compared to staying on the arterial could warrant a DDI over a SPUI.

That was the reasoning for the first full DDI in the Phoenix area at Happy Valley Rd and I-17.

[tolbs17]

SPUIs and Parclo B4s are more appropriate for main highways.

DDIs and Dumbbells (and dogbones) are for small arterials.

Not even small arterials for DDIs. Major arterials with tons of traffic entering or exiting the freeway compared to staying on the arterial could warrant a DDI over a SPUI.

In that case, I would go with a Parclo.

[tolbs17]

SPUIs and Parclo B4s are more appropriate for main highways.

DDIs and Dumbbells (and dogbones) are for small arterials.

Not even small arterials for DDIs. Major arterials with tons of traffic entering or exiting the freeway compared to staying on the arterial could warrant a DDI over a SPUI.

That was the reasoning for the first full DDI in the Phoenix area at Happy Valley Rd and I-17.

Not a major highway.

[SkyPesos]

SPUIs and Parclo B4s are more appropriate for main highways.

DDIs and Dumbbells (and dogbones) are for small arterials.

Not even small arterials for DDIs. Major arterials with tons of traffic entering or exiting the freeway compared to staying on the arterial could warrant a DDI over a SPUI.

That was the reasoning for the first full DDI in the Phoenix area at Happy Valley Rd and I-17.

Not a major highway.

Is 6 lanes not wide enough for an arterial?

[tolbs17]

SPUIs and Parclo B4s are more appropriate for main highways.

DDIs and Dumbbells (and dogbones) are for small arterials.

Not even small arterials for DDIs. Major arterials with tons of traffic entering or exiting the freeway compared to staying on the arterial could warrant a DDI over a SPUI.

That was the reasoning for the first full DDI in the Phoenix area at Happy Valley Rd and I-17.

Not a major highway.

Is 6 lanes not wide enough for an arterial?

Oh, it's wide. Just not an expressway design.

[US 89]

SPUIs and Parclo B4s are more appropriate for main highways.

DDIs and Dumbbells (and dogbones) are for small arterials.

Not even small arterials for DDIs. Major arterials with tons of traffic entering or exiting the freeway compared to staying on the arterial could warrant a DDI over a SPUI.

That was the reasoning for the first full DDI in the Phoenix area at Happy Valley Rd and I-17.

Not a major highway.

Is 6 lanes not wide enough for an arterial?

Oh, it's wide. Just not an expressway design.

Try Bangerter Highway and SR 201 in western Salt Lake City, then. For an idea of how much traffic turns there, look how many left turn lanes there are from westbound 201. Traffic still routinely backs up onto the mainline at that exit.

[tolbs17]

Battleground Ave and Lawndale Dr, they went with a SPUI because a DDI would have taken up more space.

And like I said, SPUIs are better if the freeway goes over the arterial and if it's a new freeway rather than upgrading the existing. In that case, the DDI is better.

Look at Six Forks Rd and US 401. I'm sure those would have been built as a diverging diamond if they were built like right now.

[ztonyg]

SPUIs and Parclo B4s are more appropriate for main highways.

DDIs and Dumbbells (and dogbones) are for small arterials.

Not even small arterials for DDIs. Major arterials with tons of traffic entering or exiting the freeway compared to staying on the arterial could warrant a DDI over a SPUI.

In that case, I would go with a Parclo.

Unless you're ADOT (Arizona) which seems to hate Parclos like a passion. There are only a handful of parclos in the entire state. It's pretty much 85% diamond, 10% SPUI, and 5% other (parclo, barbell, DDI) here.

[SkyPesos]

SPUIs and Parclo B4s are more appropriate for main highways.

DDIs and Dumbbells (and dogbones) are for small arterials.

Not even small arterials for DDIs. Major arterials with tons of traffic entering or exiting the freeway compared to staying on the arterial could warrant a DDI over a SPUI.

In that case, I would go with a Parclo.

Unless you're ADOT (Arizona) which seems to hate Parclos like a passion. There are only a handful of parclos in the entire state. It's pretty much 85% diamond, 10% SPUI, and 5% other (parclo, barbell, DDI) here.

Sounds like the opposite of Ontario. A4 Parclos seem like the go-to there, which I don't mind, as it's a solid design. I think someone else here mentioned it yesterday in the Best Interchange Designs thread.

[tolbs17]

Look at INDOT with their full cloverleafs being converted to Parclos.

[webny99]

Is 6 lanes not wide enough for an arterial?

Oh, it's wide. Just not an expressway design.

Try Bangerter Highway and SR 201 in western Salt Lake City, then. For an idea of how much traffic turns there, look how many left turn lanes there are from westbound 201. Traffic still routinely backs up onto the mainline at that exit.

Could that be a problem with the signal timing? It seems ridiculous that it would still back up onto the freeway with three left turn lanes. The only comparable example I can think of is I-490 at NY 441, and even though the right lane of I-490 is often slow approaching the exit, I've never known the line for the signal to back right up onto the freeway.

[kphoger]

How about an improved diamond interchange?

Isn't that what a DDI is?

That's what two of the three letters stand for, after all!

As for the third letter, though, Diverging ≠ Improved.

Or at least, they're not synonyms, even if you could argue that something could be both at once.

I get it.  But, if agencies didn't consider the DDI to be an improvement, then they wouldn't design them at all.  After all, a standard diamond interchange (SDI?) is cheaper.

[webny99]

How about an improved diamond interchange?

Isn't that what a DDI is?

That's what two of the three letters stand for, after all!

As for the third letter, though, Diverging ≠ Improved.

Or at least, they're not synonyms, even if you could argue that something could be both at once.

I get it.  But, if agencies didn't consider the DDI to be an improvement, then they wouldn't design them at all.  After all, a standard diamond interchange (SDI?) is cheaper.

And of course, there are many different aspects of "improved", traffic flow and safety being chief among them. You could argue - and I'm sure people have - that the DDI improves some aspects but not others.

[tolbs17]

Would the SPUI or DDI be better for the US 17/70 and Dr. MLK JR Blvd interchange in New Bern?

[vdeane]

Battleground Ave and Lawndale Dr, they went with a SPUI because a DDI would have taken up more space.

And like I said, SPUIs are better if the freeway goes over the arterial and if it's a new freeway rather than upgrading the existing. In that case, the DDI is better.

Look at Six Forks Rd and US 401. I'm sure those would have been built as a diverging diamond if they were built like right now.

More space?  Maybe for one of those jumbo things a lot of DOTs seem to install for whatever reason, but they don't have to take up any more room than a standard diamond.

[tolbs17]

Battleground Ave and Lawndale Dr, they went with a SPUI because a DDI would have taken up more space.

And like I said, SPUIs are better if the freeway goes over the arterial and if it's a new freeway rather than upgrading the existing. In that case, the DDI is better.

Look at Six Forks Rd and US 401. I'm sure those would have been built as a diverging diamond if they were built like right now.

More space?  Maybe for one of those jumbo things a lot of DOTs seem to install for whatever reason, but they don't have to take up any more room than a standard diamond.

Those are wider interchanges compared to the one on friendly avenue

[vdeane]

Battleground Ave and Lawndale Dr, they went with a SPUI because a DDI would have taken up more space.

And like I said, SPUIs are better if the freeway goes over the arterial and if it's a new freeway rather than upgrading the existing. In that case, the DDI is better.

Look at Six Forks Rd and US 401. I'm sure those would have been built as a diverging diamond if they were built like right now.

More space?  Maybe for one of those jumbo things a lot of DOTs seem to install for whatever reason, but they don't have to take up any more room than a standard diamond.

Those are wider interchanges compared to the one on friendly avenue

Friendly Avenue? 

[SkyPesos]

Battleground Ave and Lawndale Dr, they went with a SPUI because a DDI would have taken up more space.

And like I said, SPUIs are better if the freeway goes over the arterial and if it's a new freeway rather than upgrading the existing. In that case, the DDI is better.

Look at Six Forks Rd and US 401. I'm sure those would have been built as a diverging diamond if they were built like right now.

More space?  Maybe for one of those jumbo things a lot of DOTs seem to install for whatever reason, but they don't have to take up any more room than a standard diamond.

Those are wider interchanges compared to the one on friendly avenue

Friendly Avenue? 

I-73 exit 104. Also, it's an SPUI, not a DDI as I imagined based on the context here.

[vdeane]

Ah.  Hard to tell what that is when "Friendly Avenue" hasn't been mentioned elsewhere in this thread by name.  In any case, the difference in the width of that interchange and the one I posted seems to be median width; looking at my example and the distance the ramp is from the freeway mainline, I'm sure it would be just as narrow if the freeway ROW was the same width.

[SkyPesos]

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.

[tolbs17]

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.

[SkyPesos]

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.