Improving the dreaded Cloverleaf

[Amtrakprod]

This forum is for complaining about cloverleafs and for finding ways to make them better.


iPhone

[hotdogPi]

How do I submit the form?

[kphoger]

Collector/distributor roads.

And where's the form?

[kphoger]

Also...

This.

Similar footprint, two bridges instead of one, no weaving

[CtrlAltDel]

This.
Similar footprint, two bridges instead of one, no weaving

The left entrances seem problematic here.

[jeffandnicole]

This form is for complaining about cloverleafs and for finding ways to make them better.


iPhone

No traffic lights...free flowing traffic...nothing wrong with them.  If they're placed in a high-volume area they will probably fail...but so will many other interchange designs.

[kphoger]

This.
Similar footprint, two bridges instead of one, no weaving

The left entrances seem problematic here.

Which is more problematic, though?  Weaving or left entrances?

[hotdogPi]

This.
Similar footprint, two bridges instead of one, no weaving

The left entrances seem problematic here.

Which is more problematic, though?  Weaving or left entrances?

Left entrances. Cloverleaf weaving affects one lane; trying to take a quick right exit after entering on the left requires crossing multiple lanes (although it might not be as much of a problem here).

[yand]

Also...

This.

Similar footprint, two bridges instead of one, no weaving

This also puts curves on one of the intersecting roads.
A cloverleaf-like design that could fit in the same/marginally larger footprint (from my youtube channel):

One of the biggest benefits of cloverleafs is you only need one short overpass, I think the cost effectiveness of cloverleafs is very hard to beat.

[hbelkins]

Left exits are OK, left entrances not so much. I hate I-66 west to I-81 south.

For low-volume cloverleafs, CD lanes help. For higher-volume ones, like I-64/I-265, you need flyovers.

[webny99]

Collector/distributor roads.

That would obviously be the single option that adds the most value, i.e. most benefit for the cost.

There is something similar - but simpler, as it doesn't involve a secondary roadway - used on I-90 in Buffalo: A lane for the second (loop) exit opens prior to the loop entrance ramp coming in, thus allowing traffic exiting at the loop to decelerate first and then merge with entering traffic, instead of doing both at once. Then said lane extends after the loop ramp exits as well, allowing entering traffic an opportunity to accelerate.

In the absence of a full c/d road, the above is the absolute minimum that should be done. Come to think of it, it's actually really strange it's not done more often; a few hundred feet of pavement on either side of the weave hardly costs anything, while making a world of difference for keeping the mainline flowing freely.

[Amtrakprod]

The problem I have is the weaving.

[1995hoo]

I've always liked this design (I-395 and VA-7 in Alexandria, Virginia). Relocates two of the loop-around ramps, and alters the approach to the remaining two, to eliminate the weave areas. I suppose it might be slightly more expensive due to the additional overpasses, but on the other hand it may be suitable for tighter spaces.

A much more expensive solution, implemented as part of the Wilson Bridge reconstruction project, can be seen on the north side of the interchange of the Beltway and Telegraph Road near Alexandria: One of the loop ramps uses an overpass to clear the other one, eliminating the weave area. (The south side of this interchange has been redesigned, but it never had two loop ramps because there was always a flyover ramp there, just not in the current configuration. Flyovers are never going to be the solution to all cloverleafs.)

[Revive 755]

A much more expensive solution, implemented as part of the Wilson Bridge reconstruction project, can be seen on the north side of the interchange of the Beltway and Telegraph Road near Alexandria: One of the loop ramps uses an overpass to clear the other one, eliminating the weave area. (The south side of this interchange has been redesigned, but it never had two loop ramps because there was always a flyover ramp there, just not in the current configuration. Flyovers are never going to be the solution to all cloverleafs.)

There's always the braided loop option that MNDOT used for I-694 at MN 252

[Ned Weasel]

It's also worth noting that it has become increasingly common to replace cloverleafs with diamonds when one of the roads is not a freeway.  There are three examples on I-35 in Kansas alone: Exit 183 for SB US 59; Exit 228B for EB US 56, NB US 69/US 169, and Shawnee Mission Parkway; and Exit 232B for NB US 69 and Roe Avenue.

My personal opinion is that, for interchanges where a free-flowing interchange is justified, the most cost-effective solution is to add C/D lanes and tighten the inner loop ramps (so no additional land acquisition is required).  Flyover ramps only become justified when certain left-turning movements through the interchange play a major role in the traffic flow of the surrounding area.

[tradephoric]

Convert them to something like this. 


https://www.google.com/maps/@28.63102,-81.38741,777m/data=!3m1!1e3

https://www.youtube.com/watch?v=B8DUMjlKqx8

[yand]

Convert them to something like this. 


https://www.google.com/maps/@28.63102,-81.38741,777m/data=!3m1!1e3

https://www.youtube.com/watch?v=B8DUMjlKqx8

Should people be physically blocked from making a u-turn? Or do people have good enough sense not to do it? Or is it sometimes permissible?

[tradephoric]

^So I'm assuming if someone takes the wrong turn you want them to be able to make a U-turn directly within the interchange design itself?  I don't think this would be necessary and/or common in these type of designs.  Here are some additional real-world examples of them:

https://www.google.com/maps/@33.91199,-84.35671,735m/data=!3m1!1e3
https://www.google.com/maps/@39.6990515,-86.1485446,810m/data=!3m1!1e3
https://www.google.com/maps/@35.47833,-97.57863,721m/data=!3m1!1e3
https://www.google.com/maps/@35.51118,-97.57637,721m/data=!3m1!1e3
https://www.google.com/maps/@28.3460328,-81.5333474,779m/data=!3m1!1e3

[sprjus4]

Convert them to something like this. 


https://www.google.com/maps/@28.63102,-81.38741,777m/data=!3m1!1e3

https://www.youtube.com/watch?v=B8DUMjlKqx8

The only issue I've got here are the left exits. Interchange designs like these have been used for decades, and they have caused problems, slower traffic impeding the left lane to exit, a load of traffic trying to merge on all at once, slowing traffic way down, increasing accident chances, etc. Why it's still being used is beyond me.

[US 89]

Convert them to something like this. 


https://www.google.com/maps/@28.63102,-81.38741,777m/data=!3m1!1e3

https://www.youtube.com/watch?v=B8DUMjlKqx8

The only issue I've got here are the left exits. Interchange designs like these have been used for decades, and they have caused problems, slower traffic impeding the left lane to exit, a load of traffic trying to merge on all at once, slowing traffic way down, increasing accident chances, etc. Why it's still being used is beyond me.

That design is no different than a parclo B4, except that there's a free-flow movement instead of a direct left turn across oncoming traffic. Add that to the fact that Maitland isn't really a freeway, and I don't have any issues with something like this.

[tradephoric]

The only issue I've got here are the left exits. Interchange designs like these have been used for decades, and they have caused problems, slower traffic impeding the left lane to exit, a load of traffic trying to merge on all at once, slowing traffic way down, increasing accident chances, etc. Why it's still being used is beyond me.

To me having left entrance/ext ramps aren't that problematic when they are along the arterial street (or even a state highway with speed limits of 55 mph or below).  Often traffic along an arterial can get jammed up approaching the freeway if both freeway on-ramps are on the right-hand side.  By having a left-turn ramp you can distribute traffic more evenly along the main arterial.  This example isn't a bad design to me as this is a freeway to arterial interchange.... people have to learn when to freak out about left-turn entrance/exits and when not to...

https://www.google.com/maps/@35.47833,-97.57863,721m/data=!3m1!1e3

[kphoger]

Who can fix the cloverleaf while still retaining its most attractive elements?

only two bridge decks (assuming a dual carriageway)
all right entrances and exits

[hotdogPi]

Who can fix the cloverleaf while still retaining its most attractive elements?

only two bridge decks (assuming a dual carriageway)
all right entrances and exits

Some variant on the roundabout in West Drayton (UK). There are similar designs for I-93 at MA 213 (no fourth leg, but one could be created if the geometry was modified slightly) and I-95 at US 1 in Topsfield, MA (the inside ramps could easily be moved to the outside, but the "change direction" ramps on US 1 aren't high speed).

[webny99]

Who can fix the cloverleaf while still retaining its most attractive elements?

only two bridge decks (assuming a dual carriageway)
all right entrances and exits

A volleyball interchange does that, but with left turns, which are no better than loop ramps.

With a super-wide median, you could get rid of all left exits or entrances, but not both.

[kphoger]

Who can fix the cloverleaf while still retaining its most attractive elements?

only two bridge decks (assuming a dual carriageway)
all right entrances and exits

Some variant on the roundabout in West Drayton (UK).

Where are you talking about?  All I see in West Drayton are roundabout-under-motorway interchanges, which have stoplights and (by nature of roundabouts) inside "entrances/exits".

A volleyball interchange does that

A volleyball interchange fulfills none of the elements of a cloverleaf:  it's not free-flowing, it has multiple bridge decks, and it has left turns.