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Author Topic: Improving the dreaded Cloverleaf  (Read 1843 times)

tradephoric

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Re: Improving the dreaded Cloverleaf
« Reply #25 on: April 22, 2019, 06:27:56 PM »

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
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kphoger

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Re: Improving the dreaded Cloverleaf
« Reply #26 on: April 22, 2019, 07:05:44 PM »

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
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Re: Improving the dreaded Cloverleaf
« Reply #27 on: April 22, 2019, 07:17:42 PM »

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).
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webny99

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Re: Improving the dreaded Cloverleaf
« Reply #28 on: April 22, 2019, 07:32:12 PM »

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.
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kphoger

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Re: Improving the dreaded Cloverleaf
« Reply #29 on: April 22, 2019, 08:51:47 PM »


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.
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Re: Improving the dreaded Cloverleaf
« Reply #30 on: April 22, 2019, 08:56:28 PM »


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".

I was looking at where the M4 intersects itself. However, I was only looking at the map, so I didn't see the stoplights.
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kphoger

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Re: Improving the dreaded Cloverleaf
« Reply #31 on: April 22, 2019, 09:18:37 PM »

I was looking at where the M4 intersects itself. However, I was only looking at the map, so I didn't see the stoplights.

You mean at the A408 & Heathrow (interchange #4)?  Yeah, that's just a roundabout interchange, functionally no different than a dogbone.
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cpzilliacus

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Re: Improving the dreaded Cloverleaf
« Reply #32 on: April 22, 2019, 10:01:36 PM »

Replace the busier movements with flyover or flyunder ramps, and keep the others.  That's what was done at the junction of U.S. 29 and MD-200 (ICC) in the Silver Spring area of Montgomery County, Maryland.  Interchange opened to traffic in about 2011, and  so far it works well.
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cpzilliacus

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Re: Improving the dreaded Cloverleaf
« Reply #33 on: April 22, 2019, 10:03:42 PM »

Removing just one leaf of a cloverleaf can reduce weave issues, as was done at the junction of I-495 and MD-97, also in Silver Spring.
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US 41

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Re: Improving the dreaded Cloverleaf
« Reply #34 on: April 22, 2019, 10:20:49 PM »

Making them bigger would fix a lot of issues. I think if the leaves were bigger it would give you more room to weave more safely. Also collector lanes fix a lot of issues. In my opinion the I-22 / I-269 interchange in Mississippi (southeast of Memphis, TN) is the perfect cloverleaf.

I also like what they did on I-80 at its interchange with I-180 in Pennsylvania. They made the bridges on I-80 wide enough to support 4 lanes and built the collector lanes in a more cost effective manner.

The biggest issues with cloverleafs in my experiences are them causing slow downs in the right lane and causing everyone to shift over to the left lane. Traffic speeding from (typically) 25 to 70 or slowing down from 70 to 25 is also a little dangerous especially with the weaving. Collector lanes seem to fix these issues and in some cases collector lanes will have slower speed limits. I know in Danville, IL, the collector lanes at the I-74 / US 150 interchange have a 40 mph speed limit.
« Last Edit: April 22, 2019, 10:29:17 PM by US 41 »
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mrsman

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Re: Improving the dreaded Cloverleaf
« Reply #35 on: April 23, 2019, 09:36:23 AM »

Removing just one leaf of a cloverleaf can reduce weave issues, as was done at the junction of I-495 and MD-97, also in Silver Spring.

Agreed.  For a freeway to arterial interchange, cloverleafs should be changed to either a parclo a4 or parclo b4.  I wish that the 495/Georgia interchange be changed to a full parclo a4, so that there is one exit (instead of two) from the inner loop.  There are already traffic signals stopping traffic on both sides of Georgia anyway.

THe problem, of course, is the sequence of exit, entrance, exit, entrance that produces weaving.  Far better to have exit, exit, entrance, entrance and this can be done with some kind of braided cloverleaf or eliminating one of the middle two ramps by parclo.

Freeway to freeway interchanges can be modified with well-placed flyovers or well-placed left side entrances and exits.  Left side entrances and exits certainly have issues, but IMO if the left lane entrance becomes its own lane on the highway (i.e. no forced merge) then there isn't any real problem.  Left side exits are even less problematic.

The Houston area has a lot of these.

Another interchange more familiar to me is in Sherman Oaks, CA.  There, 405 exit ramps to the right and then merges into the left lane of 101.  (This is for both of the "left turn" movements from 405 to 101).  Since the exit becomes its own lane, there is no immediate merging issues. Of course, it would be difficult to merge if you need to take the next exit, so people in the know would only transfer from 405 to 101 left if driving at least 2 miles (exit at White Oak  westbound or Woodman eastbound or beyond).  If I wanted to go from 405 N to 101 N to Balboa, I might instead just stay on 405 and exit at a surface street like Burbank or Victory and just take surface streets to Balboa to avoid the merges.  If I'm taking 405 to 101 and driving to Calabasas or further, the interchange works fine.


https://www.google.com/maps/place/Sherman+Oaks,+Los+Angeles,+CA/@34.1586198,-118.4721994,16z/data=!4m5!3m4!1s0x80c297dba79cbcf3:0x39b4e3f8071ff16!8m2!3d34.1489719!4d-118.451357


Here is a nearby example of a braided cloverleaf at 170 at Victory Blvd:

https://www.google.com/maps/place/Sherman+Oaks,+Los+Angeles,+CA/@34.187033,-118.4037058,16z/data=!4m5!3m4!1s0x80c297dba79cbcf3:0x39b4e3f8071ff16!8m2!3d34.1489719!4d-118.451357
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webny99

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Re: Improving the dreaded Cloverleaf
« Reply #36 on: April 23, 2019, 03:02:03 PM »

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.

Shoot, I wasn't thinking about the additional bridge decks until I looked at one on a map.
While it does have left turns, it has all right entrances and exits from the freeway mainlines, so it still fulfills one of your two requirements.
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MCRoads

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Re: Improving the dreaded Cloverleaf
« Reply #37 on: April 24, 2019, 10:05:20 AM »

Well, I think the best way to save a cloverleaf interchange is to add flyover ramps. Interestingly, if most (or all) of the loop ramps with flyovers, may become a clover stack, or a full stack.
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yand

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Re: Improving the dreaded Cloverleaf
« Reply #38 on: April 24, 2019, 02:57:43 PM »

It seems to me that every suggested improvement other than C/D roads would replace rather than improve the cloverleaf. If an interchange is using a cloverleaf it's because it doesn't deserve something better  :biggrin:
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mrsman

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Re: Improving the dreaded Cloverleaf
« Reply #39 on: April 25, 2019, 07:40:53 AM »

It seems to me that every suggested improvement other than C/D roads would replace rather than improve the cloverleaf. If an interchange is using a cloverleaf it's because it doesn't deserve something better  :biggrin:

Not necessarily.  A cloverleaf is a very old design and was the standard for freeway to freeway interchanges for a long time.  Plus, flyover ramps greatly increase the cost as you add bridges over the whole interchange.  For the most part, a cloverleaf has one freeway bridged over the other (true of every fwy to fwy interchange) and then every other movement is connected via a ramp that does not bridge over other movements.  In that regard, the cloverleaf is cheaper than something like a stack.

Many cloverleafs should be replaced with something else, but often times, the DOTs lack the money.  Cloverleaf to parclo conversions are relatively inexpensive since you are keeping most of what is there, but this won't work on a fwy to fwy interchange.

EDITED TO ADD:

There is a thread in Pac SW about 880/101.  This is an old interchange in San Jose.  Many of the loop movements are no longer so important because of newer freeways like 237 and 280 that short cut some of the movements.  Also, some of the movements can be rerouted onto surface streets, as is currently done with Old Bayshore Hwy.  Obviously not ideal, but if a loop movement that causes a lot of weaving (but doesn't carry much traffic) is simply eliminated it may improve mainline traffic. 

https://www.aaroads.com/forum/index.php?board=29.0

And yes, it is cheaper to sign a surface street connector than to add a flyover.
« Last Edit: April 25, 2019, 03:57:14 PM by mrsman »
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kphoger

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Re: Improving the dreaded Cloverleaf
« Reply #40 on: April 25, 2019, 05:18:58 PM »



Obviously, this would have limited application.
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mrsman

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Re: Improving the dreaded Cloverleaf
« Reply #41 on: April 25, 2019, 06:36:17 PM »



Obviously, this would have limited application.

But it would work at a fwy/arterial interchange where the arterial has a wide enough ROW for Michigan lefts.  Basically combine parclo b4 with a Michigan left.  No need to turn across traffic to the fwy entrance, use the Mich left instead.

And as far as "arterials" go, this could even work for some types of semi-freeways like Jersey freeways, expressways, and other semi-limited roadways that aren't full freeways, but still want to restrict signals and cross traffic as much as possible
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Re: Improving the dreaded Cloverleaf
« Reply #42 on: April 25, 2019, 08:13:04 PM »

Don't forget about the braided cloverleaf:

Here is US 50's cloverleaf with I-495 in Merrifield VA with braided ramps utilized for a SPUI interchange on each side of the Beltway...

https://goo.gl/maps/mQ21ejB8Yct

In Washington, the highest volume cloverleaf would almost certainly be the 167/405 cloverleaf. There's an overpass for one of the movements, but the movement is still a loop, and the interchange is still very recognisable as a cloverleaf. At all times of day (even at 2 am), the southbound to southbound cloverleaf (the one with the overpass) backs up well before the interchange. Some directional ramps for the HOV lanes should help improve things next year:

https://goo.gl/VZy5bL



and a California example:
https://www.google.com/maps/@34.1866034,-118.4009598,17.5z
« Last Edit: April 25, 2019, 08:17:04 PM by johndoe »
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AlexandriaVA

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Re: Improving the dreaded Cloverleaf
« Reply #43 on: April 25, 2019, 08:29:10 PM »

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.

My exit...use it every day  :sombrero:

EDIT: Since you're talking DC area, what do you think about the North Cap Street cloverleaf (https://www.google.com/maps/@38.9315345,-77.0085404,17z)? I always thought this was totally random...the only cloverleaf in the city, and it's not even on a freeway.
« Last Edit: April 25, 2019, 08:31:25 PM by AlexandriaVA »
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PHLBOS

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Re: Improving the dreaded Cloverleaf
« Reply #44 on: April 26, 2019, 04:42:18 PM »

Since you're talking DC area, what do you think about the North Cap Street cloverleaf (https://www.google.com/maps/@38.9315345,-77.0085404,17z) ? I always thought this was totally random...the only cloverleaf in the city, and it's not even on a freeway.
Above-Google Map link fixed; had to place a space between the parenthesis and the question mark to get the link to go to the right location.

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thspfc

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Re: Improving the dreaded Cloverleaf
« Reply #45 on: April 26, 2019, 05:03:07 PM »

IMO, Cloverleafs at less busy interchanges (where a rural interstate meets a rural interstate for example), aren't bad. When there are cloverleaf ramps where there should be flyovers, that's dangerous.
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Brandon

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Re: Improving the dreaded Cloverleaf
« Reply #46 on: April 26, 2019, 05:45:38 PM »



Obviously, this would have limited application.

Isn't something similar already in use in Mexico?
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Re: Improving the dreaded Cloverleaf
« Reply #47 on: April 27, 2019, 10:49:32 AM »

Lends itself to all sorts of TWSS-type jokes. If you drive through the cloverbone, does that make you a boner?
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D-Dey65

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Re: Improving the dreaded Cloverleaf
« Reply #48 on: April 27, 2019, 11:37:52 AM »

Collector/distributor roads.
I'd like to see that on the Bruckner Expressway between Buckner Boulevard and Gun Hill Road (or Baychester Avenue), but with no access to the Pelham Parkway and Hutchinson River Parkway interchanges.
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Re: Improving the dreaded Cloverleaf
« Reply #49 on: April 27, 2019, 04:45:27 PM »



Obviously, this would have limited application.

Isn't something similar already in use in Mexico?

There's this:  https://goo.gl/maps/RLfUJmjzXiuXfrCLA

Ramps for the right-turn movements between the expressway and the crossing arterial, and jughandles on the arterial to complete the left-turn movements.
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