Diverging Diamond Interchange

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Re: Diverging Diamond Interchange

Postby gettingthere » Thu Aug 18, 2011 3:37 am

And what is the logic with this so called 'double diamond' crossing? To cause a head-on collision when someone doesn't think for a second and ends up on the incorrect side of the road?

And what purpose does this serve? Something similar to a traffic circle but more efficient?
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Re: Diverging Diamond Interchange

Postby bgodette » Thu Aug 18, 2011 4:55 am

gettingthere wrote:And what is the logic with this so called 'double diamond' crossing? To cause a head-on collision when someone doesn't think for a second and ends up on the incorrect side of the road?

And what purpose does this serve? Something similar to a traffic circle but more efficient?
I think the "issue" that it tries to solve is asshats making a left from freeway exit that enter and block intersections when the traffic is backed up, thereby causing a secondary jam on the crossing street. But it really doesn't, now it just moves the asshat point a little bit further out on the crossing street to the crossings on either side.

The SPUI works far far better than this ever could as it's controlled by what's effectively a single set of lights. It's a normal intersection writ large and prevents "lets zoom down the exit lane and up the ramp, through the exit intersection and down the entrance ramp back onto the jammed freeway" maneuver that just makes the jam worse for everyone else as you merge again.
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Re: Diverging Diamond Interchange

Postby ircphoenix » Thu Aug 18, 2011 5:09 am

I'm pretty sure that I just wrecked my car from even LOOKING at these interchanges. Thanks guys. Thanks.
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Re: Diverging Diamond Interchange

Postby AlanOfTheBerg » Thu Aug 18, 2011 5:10 am

Use the links previously in this thread to read more about them. They actually improve traffic flow dramatically.
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Diverging Diamond Interchange

Postby gettingthere » Thu Aug 18, 2011 5:28 am

Ok. You caught me. I didn't read the entire thread.
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Re: Diverging Diamond Interchange

Postby bgodette » Thu Aug 18, 2011 5:44 am

AlanOfTheBerg wrote:Use the links previously in this thread to read more about them. They actually improve traffic flow dramatically.
I did and I'm just not seeing the improvement over an SPUI for vehicle traffic, it just moves the problem a little further away while adding an expense of driver confusion for the first few they encounter. It might be better for interchanges with pedestrian and bicycle traffic however.

Think about it this way, what happens when the on-ramp gets backed up to the point where the tail is reaching the crossing points, then add in some yahoo parking his SUV right in the middle of it. Same thing as conventional diamonds.
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Re: Diverging Diamond Interchange

Postby AlanOfTheBerg » Thu Aug 18, 2011 3:47 pm

There is no way to remove all problems. You call out one exception which affects both types of interchange flow. I can't argue with that. Add lanes to the ramp would help for a while.

[OT]
The best way to remove traffic bottlenecks is to remove traffic. :) This means combining carpooling, massive increases in mass transit, specifically buses and trains, alternative personal transportation, massive internet infrastructure increase to make telecommuting a true reality for more workers, and reduce suburban sprawl by capping allowed children per family at 2.
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Re: Diverging Diamond Interchange

Postby Daknife » Wed Apr 18, 2012 2:16 am

This is a rather old thread, but I wanted to add the insight of someone who regularly drives through both DDI's and SPUI's. While both are very efficient, the DDI is actually much more difficult to make a deadly mistake on. The first time I drove through a SPUI, it was early in the morning and I turned a little too far left and found myself on the wrong side of the center divider. Had there been any oncoming traffic there could have been an accident. And that was a newly opened interchange with nice bright paint marking the lines. With a DDI there is no question as to which way you are to go, to turn into oncoming traffic requires an intentional excessive angle turn to the right. It's intuitive, no wondering if you're following the right dashed line.

At first these looked confusing, but after a couple times through I decided they are just the opposite. Now they are cropping up all over the place. As to space requirements compared to a SPUI, the SPUI's in Utah are much wider than a traditional interchange, DDI's are much longer. A couple DDI's that have just opened fit into the space much better than a SPUI would have. The DDI's pushed a interchange back away from the freeway, but required no buildings and very little non-road land land

https://www.waze.com/editor/?zoom=5&lat=40.43123&lon=-111.89165&layers=TFFTFFFFFFTFTFTFFTTTT This one put turn restrictions on the intersection immediately to the west of I-15 and the main stop light was moved to the next intersection to the west. As it was built in an existing underpass it simply couldn't get any wider and it didn't. The whole set of intersections all flow so much more smoothly now than they did before the rebuild. Nobody get's caught waiting in the middle of an intersection waiting to turn left. Which ever way you want to turn, you just get to the appropriate travel lane and take the turn as you move with the flow of traffic. These really do work very well.
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