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Old December 18th, 2012, 06:53 AM   #8561
diablo234
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Here are some plans for a diverging diamond interchange (the first in Texas) located at the I-35/University Blvd exit in Round Rock (a suburb just north of Austin).



http://impactnews.com/articles/the-f...otos.html#4249
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Old December 18th, 2012, 08:02 AM   #8562
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Quote:
Originally Posted by Hudson11 View Post
Thruway head backs $3.1 Billion TZB proposal

http://www.lohud.com/article/2012121...medium=twitter



Have people started calling it The Clothespins yet?
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Old December 18th, 2012, 12:46 PM   #8563
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Quote:
Originally Posted by diablo234 View Post
Here are some plans for a diverging diamond interchange (the first in Texas) located at the I-35/University Blvd exit in Round Rock (a suburb just north of Austin).



http://impactnews.com/articles/the-f...otos.html#4249
Can someone explain to me what's up with that? Why have lanes going in the wrong direction and confusing some people when you can have them goign the right way like every other place on Earth?
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Old December 18th, 2012, 01:56 PM   #8564
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Originally Posted by siamu maharaj View Post
Can someone explain to me what's up with that? Why have lanes going in the wrong direction and confusing some people when you can have them goign the right way like every other place on Earth?
Well it increases traffic flow for starters. Here is a video which explains the benefit of this interchange in further detail.

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Old December 18th, 2012, 04:05 PM   #8565
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Minnesota has 2 diverging diamond interchanges under construction as we speak. I guess they work well where you have high turning volumes.
They save a lot of money in bridge costs since you dont need turn lanes on top of the bridge.
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Old December 18th, 2012, 04:28 PM   #8566
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Old December 18th, 2012, 04:56 PM   #8567
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... what you think.
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Old December 18th, 2012, 05:40 PM   #8568
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Diverging Diamonds have their own set of problems. They do not do a good job at maintaining coordination along the arterial because the DDI traffic signals often have to run a much shorter cycle than the surrounding signals. In the case of Utah, they have DDI's that run completely free from the surrounding signals meaning it's a crap shoot if you hit a green light or not.

Ever been stopped at a red light looking at a signal resting in green 700 feet up the road with no cars traveling thru the intersection... then proceed to get your green and come straight to a red light at the signal you were just staring at?
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Old December 18th, 2012, 07:46 PM   #8569
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You've described nearly every traffic light in Florida lol.
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Old December 18th, 2012, 08:17 PM   #8570
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New imagery of the 11th Street Bridges (I-295 / I-695 connector) in Washington, D.C.

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Old December 18th, 2012, 08:56 PM   #8571
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Quote:
Originally Posted by diablo234 View Post
Well it increases traffic flow for starters. Here is a video which explains the benefit of this interchange in further detail.

Well yeah, but don't people get confused? I bet I'd have been confused if I'd ever come across it. Maybe they use a lot of signs leading up to it?
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Old December 18th, 2012, 09:00 PM   #8572
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I've posted this time-distance in the past but it really highlights the concept of signal spacing and the effects it has on progression. Good signal progression in one direction leads to bad progression in the opposite direction along the time distance diagram below. Whenever you have two traffic signals spaced roughly 1/2 mile apart along a high speed arterial good progression goes out the window in at least one direction of travel.


The Diverging Diamond naturally lead to these tough "1/2 mile" spacings that are so difficult to deal with (since the DDI calls for traffic signals that stop Both directions of travel along the arterial). The Diverging Diamond interchange contributes to the problem of poor traffic signal spacing that is so prevalent throughout major metros in America.
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Old December 18th, 2012, 11:51 PM   #8573
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I kept track of new freeway openings in the United States this year.

In 2012, 231 miles of new freeway opened to traffic in 13 states (as of today). Indiana opened the most, with 67 miles of new freeway, all of it belongs to I-69. Follow-up is Texas with 48 miles of new freeway. Wisconsin comes in third with 31 miles of new freeway. California and Missouri opened just 3 miles each. I excluded the upgrade of US 71 to I-49 in Missouri because most of it was done prior to 2012.

This includes Interstate Highways, U.S. Highways and State Highways built to freeway standards.
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Old December 19th, 2012, 12:14 AM   #8574
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Quote:
Originally Posted by siamu maharaj View Post
Well yeah, but don't people get confused? I bet I'd have been confused if I'd ever come across it. Maybe they use a lot of signs leading up to it?
Well there are signs in place to guide motorists in place.

Here is a a video of a diverging diamond interchange from the driver's viewpoint in American Fork, Utah. As you can see it's not really complicated.

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Old December 19th, 2012, 12:17 AM   #8575
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Quote:
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New imagery of the 11th Street Bridges (I-295 / I-695 connector) in Washington, D.C.

I am surprised this has not been done already, hopefully it will get more traffic off New York Avenue (US 50).
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Old December 19th, 2012, 01:02 AM   #8576
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Quote:
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The new "Tappan Zee Bridge brought to you by Honda!"

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Old December 19th, 2012, 01:26 AM   #8577
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Quote:
Originally Posted by tradephoric View Post
Diverging Diamonds have their own set of problems. They do not do a good job at maintaining coordination along the arterial because the DDI traffic signals often have to run a much shorter cycle than the surrounding signals. In the case of Utah, they have DDI's that run completely free from the surrounding signals meaning it's a crap shoot if you hit a green light or not.

Ever been stopped at a red light looking at a signal resting in green 700 feet up the road with no cars traveling thru the intersection... then proceed to get your green and come straight to a red light at the signal you were just staring at?
But I think that the whole idea of DDI works best in places where there is a lot of traffic entering/leaving freeway. If most of the traffic is turning into freeway or coming from the freeway then synchronization along the arterial doesn't matter that much as relatively fewer cars drive just straight through the interchange.
In places where very few drivers turn from the arterial to freeway then DDI might loose some of it advantages by blocking through traffic and disturbing synchronization.
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Old December 19th, 2012, 04:47 AM   #8578
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Quote:
Originally Posted by diablo234 View Post
I am surprised this has not been done already, hopefully it will get more traffic off New York Avenue (US 50).
I'd be surprised if it did. 50's pretty far north of this location... as far as the Anacostia Freeway is concerned anyway.
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Old December 19th, 2012, 05:34 AM   #8579
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Speaking as someone who occasionally drives into Washington from the northeast and who's gotten to the point where I'd rather go around the Beltway to Cabin John and take the GW in than use New York, or 16th or Connecticut.... I'd be glad to stay on the Anacostia for a few miles farther if it meant I could stay on freeways right downtown.
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Old December 19th, 2012, 05:37 AM   #8580
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Quote:
Originally Posted by Professor L Gee View Post
I'd be surprised if it did. 50's pretty far north of this location... as far as the Anacostia Freeway is concerned anyway.
I was thinking more in terms of traffic getting from say the Maryland suburbs to DCA/Arlington since through traffic heading to those destinations as of right now still has to utilize US 50 which is incredibly time consuming, with the new connection to the Anacostia Freeway they can effectively bypass the traffic lights/congestion on New York Avenue (although traffic heading into DC proper as the final destination will still probably use New York Avenue regardless).
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