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Old June 7th, 2007, 11:34 PM   #301
Paddington
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1. They cost too much to build.
America is a rich country.

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2. The many bridges destroy the sight for the drivers.
I've never heard that one before. What do you need to look up at the sky at all times or something? The road visibility is just fine on a stack interchange.


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Hmm.. don't get the point, it stops traffic, not only for those that wants to enter to the left, but also on the upper road. Wouldn't an ordinary cloverleaf work better here?


Should be upgraded into a CL. It seems that it barely can handle the traffic. Having traffic lights in a congested intersection doesn't make any sense.
Not really. Many cloverleafs (connecting city roads and expressways) in the U.S. have been replaced with SPUI interchanges. A SPUI does have the drawback of one traffic light on the surface road (and lights on the left turn lanes of the ramps), but it allows for concurrent left turns. It takes up much less space than a cloverleaf, and moves traffic faster than a typical diamond interchange and perhaps faster than a cloverleaf in certain situations (high traffic areas with lots of weaving). SPUI interchanges are also better for pedestrians than cloverleafs.
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Old June 8th, 2007, 12:10 AM   #302
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America is a rich country.
I bet you won't give this reason to your boss in order to explain the cost of your proposed project
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Old June 8th, 2007, 02:42 AM   #303
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I bet you won't give this reason to your boss in order to explain the cost of your proposed project
They spent a few dollars on this one:



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Old June 8th, 2007, 03:05 AM   #304
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We are still talking about cost vs. benefits, right? For instance, Bay Area's I-80 and I-880 junction had to be stack interchange because there was no other alternatives. Therefore, I think neither you nor fetg_ are right arguing about different things. You have to look at each particular case to decide what will be better.
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Old June 8th, 2007, 03:09 AM   #305
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Cloverleafs have too many inherent points of conflict, even with C/D roads. More modern designs are superior. Stacks have their drawbacks, but they are the best for throughput.
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Old June 8th, 2007, 03:43 AM   #306
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We are still talking about cost vs. benefits, right? For instance, Bay Area's I-80 and I-880 junction had to be stack interchange because there was no other alternatives. Therefore, I think neither you nor fetg_ are right arguing about different things. You have to look at each particular case to decide what will be better.
That's true, but what I do know is that we build very few cloverleafs today and are replacing many of the old ones. Back in the 1950's and 1960's almost all interchanges were cloverleafs. These days, the most common surface road-expressway interchange is the diamond, especially in the suburban areas where most of the growth is. For expressway-expressway interchanges, symmetric four level stacks are popular in the South West, and elsewhere in the country cloverleaf-flyover combinations and asymmetric flyover-stack hybrids are more typical of modern construction.

A lot of the old cloverleafs are being replaced with partial cloverleafs and SPUI's where they interchange with city roads, and cloverleaf-flyover combinations where they interchange with other expressways.

Last edited by Paddington; June 8th, 2007 at 03:53 AM.
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Old June 8th, 2007, 09:17 AM   #307
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I hate cloverleafs with a passion. If it were up to me, every interchange in urban areas would be either a stack, modified stack, or SPUI. Diamond interchanges work fine in rural areas.
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Old June 8th, 2007, 12:10 PM   #308
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America is a rich country.
But Americans doesn't like to pay taxes

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I've never heard that one before. What do you need to look up at the sky at all times or something? The road visibility is just fine on a stack interchange.
Better sight by more more space.

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Not really. Many cloverleafs (connecting city roads and expressways) in the U.S. have been replaced with SPUI interchanges. A SPUI does have the drawback of one traffic light on the surface road (and lights on the left turn lanes of the ramps), but it allows for concurrent left turns. It takes up much less space than a cloverleaf, and moves traffic faster than a typical diamond interchange and perhaps faster than a cloverleaf in certain situations (high traffic areas with lots of weaving). SPUI interchanges are also better for pedestrians than cloverleafs.
Better than diamonds, but are they really half as good as CLs? Considering that traffic light is used, it wastes time for drivers and create traffic stocks. Only a minority of the traffic use the loops. Why not put up traffic light in an existing CL instead?
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Old June 8th, 2007, 12:14 PM   #309
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Cloverleafs have too many inherent points of conflict, even with C/D roads. More modern designs are superior. Stacks have their drawbacks, but they are the best for throughput.
You may replace extremely busy loops with one flyover. It's possible to eliminate all weaving with just two flyovers.
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Old June 8th, 2007, 01:14 PM   #310
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Diamond interchanges work fine in rural areas.
I hope you mean exits, and not interchanging freeways.

We have some grade interchanges, and they cause a lot of traffic jams and pollution.

Cloverleafs have one advantage, when an outside connecting road is closed (for roadworks/accidents), you can go 3 times through the "leaf" and still go to the right direction. With flyovers, you can't, and have to turn on the next exit.
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Old June 8th, 2007, 05:07 PM   #311
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You may replace extremely busy loops with one flyover. It's possible to eliminate all weaving with just two flyovers.
Let's not forget the problem of big trucks flipping over on loops due to excess speed. The extremely low speed that they must navigate the interchange at is a significant problem that can only be addressed by lengthening the distance traveled through the interchange.

Chris: In the US, "interchange" is often used to mean any intersection with a freeway, regardless of the type of road.
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Old June 8th, 2007, 05:25 PM   #312
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how do you call an interchange between Freeways? Intersection? Junction?
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Old June 8th, 2007, 05:43 PM   #313
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Cloverleafs have one advantage, when an outside connecting road is closed (for roadworks/accidents), you can go 3 times through the "leaf" and still go to the right direction. With flyovers, you can't, and have to turn on the next exit.
Exactly.. not to mention that by building stacks, you get kinda locked for future expansion plans.

Anyway, I have three suggestions for how to modifie cloverleafs in order to make them fit better(I'm no artist, so they might not look perfect, but they should be simple to understand). If something is unclear, I can make a new image with greater details.

1. Space saving cloverleaf. This can replace daimonds and SPUs that face capacity problems. Might not handle capacity as well as a traditional cloverleaf. It's a diamond with the extra feature of inner roads. It can also replace traditional CLs when space is needed and when traffic is low.


2. Cloverleaf roundabout. I've only drawed the C/D roads/ramps. This is a cloverleaf with roundabout-rules applied to the four loops where incoming traffic will enter. So there will be no weaving issues. This is better than any roundabout interchange that exists today and because you only pass one ingoing roads, instead of three, as with the Manchesters famous M-way rouandabout. That, apart from the fact that it's way cheaper to build.


3. Cloverleaf with two flyovers. This is the alternative that can take the same capacity as a four-level stack, but is cheaper to build, cheaper to extend and looks better.
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Old June 8th, 2007, 05:45 PM   #314
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Let's not forget the problem of big trucks flipping over on loops due to excess speed. The extremely low speed that they must navigate the interchange at is a significant problem that can only be addressed by lengthening the distance traveled through the interchange.
Than make the loops to lean inwards. Problem solved.
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Old June 8th, 2007, 05:58 PM   #315
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Those loops have not such a good capacity. You might get stuck in a traffic jam when a lot of weaving exists.

However, i've never seen a loop with more than 1 lane.
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Old June 8th, 2007, 08:16 PM   #316
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Those loops have not such a good capacity. You might get stuck in a traffic jam when a lot of weaving exists.

However, i've never seen a loop with more than 1 lane.
Well, two lane loops can exist as long as there is flyovers to prevent weaving. See my third suggestion.

The cloverabout(second suggestion) handles weaving by making the cloverleaf with roundabout design and roundabout rules. Such can have 2-3 lines. The entrances/exits can be wider, since they are more important.
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Old June 8th, 2007, 08:16 PM   #317
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I hate cloverleafs with a passion. If it were up to me, every interchange in urban areas would be either a stack, modified stack, or SPUI. Diamond interchanges work fine in rural areas.
IMHO, the worst 'urban' cloverleaf interchange is I-90 (Northwest Tollway)/290/IL 53 in Schaumburg, IL. Two 8 lane highways meet there.

http://maps.google.com/?ie=UTF8&ll=4...&t=k&z=14&om=1

A couple of other not-so-good ones are I-39/90/90/US 151 in Madison, WI (WisDOT recently added collector/distributor lanes to the interstate side of that interchange to take care of a bad weaving safety problem there) and I-39/43/90/WI 81 in Beloit, WI (that one needs flyovers and a better separation from local streets).

For the most part, cloverleafs can and do work very well for freeway-freeway junctions in more rural places where most of the vehicles stay on the routes that they are already on.

A few examples of this are I-35/90 at Albert Lea, MN, I-35/US 20 at Williams, IA, I-43/US 12 at Elkhorn, WI, I-39/80 at LaSalle-Peru, IL and I-39/88 (Reagan Tollway) at Rochelle, IL.
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Old June 8th, 2007, 11:09 PM   #318
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how do you call an interchange between Freeways? Intersection? Junction?
Usually that is just called an interchange as well.

Oh, and superelevating the curves on a cloverleaf? That doesn't really help, either. The circumference of the curves is simply too small for many trucks to navigate them safely, and given the weight of many trucks, the superelevation can be even more dangerous.
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Old June 9th, 2007, 12:39 AM   #319
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Oh, and superelevating the curves on a cloverleaf? That doesn't really help, either.
Yes it does help, since the truck can drive faster and still keep the truck on the road.

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The circumference of the curves is simply too small for many trucks to navigate them safely, and given the weight of many trucks, the superelevation can be even more dangerous.
If that's a problem for trucks, then what about standard trumpet interchanges? You have the same loop there. The solution is usually to drive slower. But according to the solution above, it's possible to drive the same speed more secure.
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Old June 9th, 2007, 03:34 AM   #320
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If that's a problem for trucks, then what about standard trumpet interchanges? You have the same loop there. The solution is usually to drive slower. But according to the solution above, it's possible to drive the same speed more secure.
The loops on trumpets cover a greater distance than on cloverleafs. To get them that large on cloverleafs would require an unreasonable amount of space. Not only that, but trumpets are not as great an idea in cities due to once again, the space concern.
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