Contraflow Parclo A4 interchange

[tradephoric]

I was thinking of an interchange design that could be a viable option to the massive DDI's being built in Florida.   They are planning to build a DDI at Martin Luther King Jr Boulevard & I-75 in the coming years 


https://www.tampabay.com/news/transportation/roads/Florida-has-a-gem-of-an-idea-to-move-traffic-on-and-off-I-75-It-s-called-diverging-diamonds_168229773

Instead of a massive DDI that takes up a lot of ROW anyways, what about a design like the model below?  Traffic entering the freeway from the arterial doesn't have to drive through any traffic signals (not the case at a DDI).  Thru traffic along the arterial only drives through one traffic signal that only stops one direction of travel (as opposed to at a DDI where traffic travels through 2 traffic lights that stop both directions of travel).  Traffic exiting the freeway turning left onto the arterial only drives through one traffic signal (in a DDI traffic exiting the freeway must pass under 2 traffic signals). 

https://www.youtube.com/watch?v=w1CLG0F2-4k
   

[Bitmapped]

Your idea is going to require a lot more lanes on/under the bridge, which tends to be expensive. I also don't see how your design requires less ROW than a DDI.

[tradephoric]

Your idea is going to require a lot more lanes on/under the bridge, which tends to be expensive. I also don't see how your design requires less ROW than a DDI.

To be fair both the model and the recently constructed DDI at University Parkway in Florida have the exact same number of lanes on/under the bridge deck.  If ROW is a concern the Contraflow Milwaukee A interchange becomes an option. 

https://www.youtube.com/watch?v=UzARS4WPpyE

[kphoger]

If ROW is a concern the Contraflow Milwaukee A interchange becomes an option. 

You know, for DOTs that have some extra bridges just lying around at the yard.

[tradephoric]

If ROW is a concern the Contraflow Milwaukee A interchange becomes an option. 

You know, for DOTs that have some extra bridges just lying around at the yard.

According to Marlena Gore, a project manager for the Florida Department of Transportation, the construction cost for the University Parkway DDI was $74.5 million.  You would think for that kind of money you could get an interchange that achieves better operational performance than the DDI they settled on.  Also if you look closely at the two models i posted , the Milwaukee A interchange has 2 fewer lanes crossing the main bridge deck compared to the Parclo A model (10 lanes as opposed to 12).  So there is a cost savings there with a shorter bridge deck over the main span. 

Admittedly, the Milwaukee A design requires two additional flyover ramps, but if that reduces ROW cost than that in itself can be a tremendous cost savings.  Here's the required footprint of the Contraflow Milwaukee A interchange juxtaposed over the existing University Parkway DDI in Florida.



Here is a real world example of a Milwaukee A interchange.  While it doesn't have contraflow lefts, you can get a sense at how compact it is.

[US 89]

According to Marlena Gore, a project manager for the Florida Department of Transportation, the construction cost for the University Parkway DDI was $74.5 million.  You would think for that kind of money you could get an interchange that achieves better operational performance than the DDI they settled on.  Also if you look closely at the two models i posted , the Milwaukee A interchange has 2 fewer lanes crossing the main bridge deck compared to the Parclo A model (10 lanes as opposed to 12).  So there is a cost savings there with a shorter bridge deck over the main span. 

Admittedly, the Milwaukee A design requires two additional flyover ramps, but if that reduces ROW cost than that in itself can be a tremendous cost savings.  Here's the required footprint of the Contraflow Milwaukee A interchange juxtaposed over the existing University Parkway DDI in Florida.



Here is a real world example of a Milwaukee A interchange.  While it doesn't have contraflow lefts, you can get a sense at how compact it is.

Not that a Milwaukee A wouldn't be cool (because it would be) but it also has four bridges, compared to the one or two bridges required for a DDI. In general, bridges eat up a lot more of the construction cost than ROW does. Also, the geometry on those loop ramps looks pretty tight; while it's doable, there's no way the advisory speed on those is any more than 20 mph, which could make for a tight merge where the merging traffic is going much slower than the freeway traffic.

Also, construction is one of those things that's ridiculously expensive in general. The next SPUI that gets built on Bangerter Highway is going to cost UDOT $64.2 million, for example.

[kphoger]

Also, the geometry on those loop ramps looks pretty tight; while it's doable, there's no way the advisory speed on those is any more than 20 mph, which could make for a tight merge where the merging traffic is going much slower than the freeway traffic.

The speed advisory is, in fact, exactly 20 mph.

[tradephoric]

Also, the geometry on those loop ramps looks pretty tight; while it's doable, there's no way the advisory speed on those is any more than 20 mph, which could make for a tight merge where the merging traffic is going much slower than the freeway traffic.

I don't see slow merge speeds onto the freeway being a big issue.  That Milwaukee interchange has nearly 1000 feet of straightaway before drivers enter the freeway.  Compared to some Parclo A4 designs where there is literally 0 feet of on-ramp straightaway before entering the freeway, 1000 feet sounds like plenty.

[tradephoric]

Not that a Milwaukee A wouldn't be cool (because it would be) but it also has four bridges, compared to the one or two bridges required for a DDI. In general, bridges eat up a lot more of the construction cost than ROW does.

Not that this would be practical at many interchanges, but there is a way to eliminate the flyover ramp bridges at a Milwaukee interchange assuming the arterial street is spread far enough apart.  I call this the "Split Milwaukee B interchange":

https://www.youtube.com/watch?v=HFlo90vZxmM

EDIT:  This design would pretty much fit in the ROW of the University Parkway DDI, believe it or not.  This design would require no additional ROW, requires only two bridge decks, and provides much more efficient operation along the arterial... not to mention the pedestrian exposure along the arterial would be much less than the existing DDI.

[vdeane]

I'm guessing this DDI takes up a lot of ROW because they had a lot of ROW from the old design and decided to use it.  A DDI need not take up that much space.

[jakeroot]

I'm guessing this DDI takes up a lot of ROW because they had a lot of ROW from the old design and decided to use it.  A DDI need not take up that much space.

This, and the R102/N2 interchange in Durban, are two great examples of tight DDI's. You don't need massive sweeping curves for DDIs to work. Good signs and markings will get the job done. Props to NYSDOT.

The Florida example is more than likely massive because the number of cars that pass through that area require that many lanes to compensate for the poor through-traffic capacity.



To Tradephoric: You could design a tighter version of the original A4 contraflow interchange. Your medians appear to be 3+ lanes wide. They really only need to be a lane apart, at most.

[kphoger]

Compared to some Parclo A4 designs where there is literally 0 feet of on-ramp straightaway before entering the freeway, 1000 feet sounds like plenty.

But that's not to say a ParClo A4 has to have zero feet of on-ramp, nor that a Milwaukee won't have zero feet of on-ramp.  Your statement is not, in fact, a comparison of the two designs themselves.

[tradephoric]

Compared to some Parclo A4 designs where there is literally 0 feet of on-ramp straightaway before entering the freeway, 1000 feet sounds like plenty.

But that's not to say a ParClo A4 has to have zero feet of on-ramp, nor that a Milwaukee won't have zero feet of on-ramp.  Your statement is not, in fact, a comparison of the two designs themselves.

In the Milwaukee interchange there needs to be a grade transition from the flyover ramp to the freeway grade.  To ensure that grade isn't too steep the flyover ramps need to be set back a good distance from the main arterial which basically ensures a decent amount of straightaway on-ramp distance.

[Bitmapped]

Your idea is going to require a lot more lanes on/under the bridge, which tends to be expensive. I also don't see how your design requires less ROW than a DDI.

To be fair both the model and the recently constructed DDI at University Parkway in Florida have the exact same number of lanes on/under the bridge deck.  If ROW is a concern the Contraflow Milwaukee A interchange becomes an option. 

Your design provides for 3 through lanes in each direction on the side road. The I-75/University Parkway DDI in Sarasota has 5 through lanes in each direction. The two situations are not equivalent.

[jakeroot]

Your idea is going to require a lot more lanes on/under the bridge, which tends to be expensive. I also don't see how your design requires less ROW than a DDI.

To be fair both the model and the recently constructed DDI at University Parkway in Florida have the exact same number of lanes on/under the bridge deck.  If ROW is a concern the Contraflow Milwaukee A interchange becomes an option. 

Your design provides for 3 through lanes in each direction on the side road. The I-75/University Parkway DDI in Sarasota has 5 through lanes in each direction. The two situations are not equivalent.

It needs 5 lanes because the arterial's capacity is handicapped by the DDI. A three or even two lane arterial with a Parclo setup likely has the same capacity as what was built in Sarasota.

Remember: it's not the number of lanes. It's how quickly the road can process cars.

[mrsman]

The interchange at I-95 and MD-175 in Columbia, MD can be known as a split-parclo A4 design.

https://www.google.com/maps/place/Columbia,+MD/@39.1764111,-76.7907194,1809m/data=!3m1!1e3!4m5!3m4!1s0x89b7dfb06369a051:0xf0d6bd65b687635d!8m2!3d39.2037144!4d-76.8610462

The carriageways on the street are split, so this provides room for the left turn ramps from the freeway to merge into traffic without traffic signals.  Essentially, the arterial is 3 lanes each direction.
The right lane of the incoming arterial forces an exit onto the freeway, while a new left lane is formed from the traffic coming in from the freeway ramp.  There is only one traffic signal on each direction of MD 175.

It seems highly efficient, I'm surprised it isn't replicated more.

[jakeroot]

It seems highly efficient, I'm surprised it isn't replicated more.

I agree that it appears very efficient, but I do wonder why they didn't try and find a bit of extra cash for an underpass for those left turns. Seems like there's plenty of room for a full-blown interchange here (probably why it's not replicated more -- not enough ROW at most interchanges).