Possible cloverleaf weaving solution?

[berberry]

I thought of this idea a couple years ago when I took a road trip from Jackson, MS to Los Angeles, CA via Amarillo, TX.  I thought of posting about it here at the time (I'm a long-time reader, rare poster, at this forum), but I can't shake the feeling that there's something I'm missing and that my idea really wouldn't work.  Can anyone tell me what's wrong with this?

First of all, assuming this will work at all, it will work ONLY where one of the intersecting roadways is not a freeway.  Also, I don't think you'd want to build an interchange like this from scratch.  If it can work at all, I thinks it's more likely to be feasible as a conversion of an existing problem cloverleaf, to be considered as an option to a parclo or cloverstack.

To one standard, full cloverleaf interchange, add CD lanes on the freeway.  To each straight ramp, add a (rush-hour-only?) left-turn option, controlled by a traffic signal where necessary.  As with many diamond interchanges, the straight ramps would be single-lanes at the point where they merge to/from the freeway or CD lane, but would be split before reaching (or after leaving) the non-freeway, with the split-off ramp accommodating, of course, the left-turning traffic to/from the non-freeway.

This would result in something like a combination of diamond and full-cloverleaf designs.  You'd have all the left-turn lanes you normally see at diamonds, but you'd also have the loop ramps as a choice for motorists.  During high-traffic periods, many motorists - and I would think almost all truckers - would likely choose to turn left rather than navigate the weaving lanes.  Other people, including those like myself who absolutely HATE sitting at traffic lights or waiting for a left-turn opportunity, would probably choose the loop ramp, except perhaps at rush hour.  And as I mentioned earlier, highway designers might choose to allow use of the left-turn lanes only at rush hour.

So what am I missing?  Could such a design help deal with the weaving issues that can become so crippling at rush hour, and thereby increase the capacity of the interchange?  This seems too crazy to ever work, but I can't figure out why not.

AbE:  After reading back through this a couple times, I see one problem I hadn't thought of before:  the close proximity of loop-ramp weaving lanes and traffic lights.  Of course, we already have that at some cloverleaf configurations - I've seen it at 3/4 and 2/4 cloverleafs, for example - but as an option for high-volume, frequently bogged-down cloverleaf interchanges that aren't quite high-volume enough to justify a full stack, this might limit the number of cases where the diamond/full-cloverleaf hybrid could work.  I would therefore consider it an option only for what otherwise would probably be a cloverleaf-to-parclo conversion.

[Scott5114]

People tend to not react well when given two options for the same thing that are better under slightly different circumstances. Exit 110 and SB I-35 in Norman, OK are kind of like this. Exit 110B (signed "Robinson St Westbound") lets out onto the service road, which traffic follows to Robinson Street, where they can turn right (W) or left (E). Exit 110A ("Robinson St") is a loop ramp which splits, so you can again turn right or left, but by using 110A you get a right turn going E and a left turn going W. Obviously the idea is to use whichever ramp will give you a right turn so you don't have to wait at the light.

Why doesn't it work? Everyone just takes the first exit that says "Robinson St". So everyone just piles onto 110B and 110A ends up with about one car or so. So the people trying to use 110B for its intended purpose (going west) cannot get through because of the swarm of people waiting to turn left. It gets severely backed up.

I have a feeling something similar would happen at your proposed interchange. People are stupid.

[Truvelo]

AbE:  After reading back through this a couple times, I see one problem I hadn't thought of before:  the close proximity of loop-ramp weaving lanes and traffic lights.  Of course, we already have that at some cloverleaf configurations - I've seen it at 3/4 and 2/4 cloverleafs, for example - but as an option for high-volume, frequently bogged-down cloverleaf interchanges that aren't quite high-volume enough to justify a full stack, this might limit the number of cases where the diamond/full-cloverleaf hybrid could work.  I would therefore consider it an option only for what otherwise would probably be a cloverleaf-to-parclo conversion.

You could install some signals that direct traffic onto the left turn lanes during rush hour and the loops during quieter periods. Perhaps red X and green ↑ could be used to show which ramps can and can't be used. That way traffic won't be making left turns by using both ramps simultaneously.

[vdeane]

The interchange of I-590 south with NY 31 has something like this.  There's a normal ramp to NY 31 (exit 2A) for traffic heading west but allows left turns at a light followed by a loop ramp to NY 31 east (exit 2B).  There isn't a huge backup problem, probably because exit 2A is signed for NY 31 west - you don't know you can make a left turn until you get to the light.  Also, the light is a VERY long wait for traffic on the ramp, so the only people that use it are going to Westfall Rd or Allens Creek Rd and can't use the ramp.

http://maps.google.com/maps?ie=UTF8&hl=en&hq=&hnear=Rochester,+Monroe,+New+York&ll=43.116257,-77.551031&spn=0.011325,0.027788&z=16

[hbelkins]

There are also two options for travelers using US 119 north in Charleston, WV to access I-64. A ramp on the right leads to a flyover, and a traffic light on the left also allows drivers to access that flyover.

[mightyace]

http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Nashville,+TN&sll=37.0625,-95.677068&sspn=32.472848,79.013672&ie=UTF8&hq=&hnear=Nashville,+Davidson,+Tennessee&ll=36.152707,-86.857395&spn=0.008074,0.01929&t=h&z=16

Even without the remaining flyover ramps on the west side of the interchange, the west side I-40/Briley Parkway/Whitebridge Rd. exit has two options to Briley north exiting west and two from Briley south entering east.  In each case, there is the flyover ramp or the original diamond ramp.

[UptownRoadGeek]

That seems dangerous in my opinion. Only because they drivers would screw up what to do. Access would have to be restricted to the different ramps at different times of the day for it to work smoothly. Close the loops and activate the light at peak time and close the left turn and deactivate the lights during off-peak.

Here are some alternative cloverleaf conversions that I've seen.
Mobile, AL



New Orleans, LA

[Truvelo]

Here are some alternative cloverleaf conversions that I've seen.

I don't like the idea of converting cloverleafs into parclos due to the addition of traffic lights. I much prefer the idea of adding bridges to remove the weaving and retaining full freeflow of all movements although I see cost being an issue.

Does a diamond interchange where some direct connectors have been added later count? This is common worldwide where the original ramps can't cope with the amount of turning traffic. Here in the UK we have several freeway to freeway interchanges with roundabouts that struggle to cope with the traffic demands. Some have had direct connectors added for the busiest movements such as the example below where north<>west movements can avoid the roundabout. In this case traffic making these turns can use either the direct connectors or the original roundabout.

http://maps.google.co.uk/?ie=UTF8&ll=53.732314,-1.51298&spn=0.008962,0.023711&t=k&z=16

[aswnl]

Reconstruction from a cloverleaf to a clover-turbine is what has been done in the Netherlands (Oudenrijn interchange). Two indirect ramps have been replaced by two semi-direct ramps.

Before: (south is to the right)


After: (south is down)

[Alps]

That seems dangerous in my opinion. Only because they drivers would screw up what to do. Access would have to be restricted to the different ramps at different times of the day for it to work smoothly. Close the loops and activate the light at peak time and close the left turn and deactivate the lights during off-peak.

Here are some alternative cloverleaf conversions that I've seen.

New Orleans, LA

Interesting thing about that one is that there is a double weave getting eliminated - Causeway between I-10 ramps and from there up to Veterans Blvd.  That's where the extra ramps are coming from.

[Truvelo]

Here's how we do it in the UK

Before

After

The map on Google is totally wrong so I've used OSM for the correct layout.

[english si]

To be fair though, not a huge amount of traffic uses that junction. I wonder why the bridges are extra-wide though - they aren't on the cloverleaf to the south (Scotland's remaining one, and half the UK's cloverleafs now), which would be busier.

Of course, killing a junction which had loads more capacity and was free-flowing is annoying.