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Thread: New Traffic Flow Pattern

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    Default New Traffic Flow Pattern

    'Diverging Diamond' Traffic Flow: Way of the Future?



    "It's not often that you can make traffic flow more smoothly and safely without spending significant time and money. But drivers in Springfield, Mo., are the first in the United States to use a new interchange design that transportation officials say is quick, cheap, and safe.
    The "diverging diamond" is being put to the test. Fans of the new highway interchange design say it improves traffic flow by eliminating problematic left turns. There's just one catch: It briefly sends all cars over to the left side of the road..."



    Read the rest here.
    Last edited by kevin.drew; 24-11-2009 at 02:26 PM.

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    More photos on how this works..







    Last edited by edmonton daily photo; 24-11-2009 at 05:13 PM.

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    Oh, I think my link is jussst fine.

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    ahh - when I first clicked your link, it didn't work...

    A very interesting idea and has potential for some current interchanges here I think.

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    It does seem interesting

    Again it prevents the ability to T-bone which is a good thing.

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    Interesting idea. Seeing it in action at the original link, it appears to have some very good potential.

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    That's actually quite interesting...I can think of several interchanges here that could benefit from this design (St. Albert Trail at Yellowhead Trail comes to mind).
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    Quote Originally Posted by RTA View Post
    That's actually quite interesting...I can think of several interchanges here that could benefit from this design (St. Albert Trail at Yellowhead Trail comes to mind).
    97 Street over the Yellowhead would be another good one.

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    ^ That one is a SPUI and may not convert as easily. A SPUI wouldn't really need this kind of upgrade anyway, left-turning traffic doesn't tend to pile up into the interchange, it typically waits outside of it for the next signal phase.
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    There is (perhaps was now) an interchange in Baltimore where they did something similar having the lanes flip over, alas reality didn't work out quite so well, they are now in the process of rebuilding it.

    Old view;
    http://maps.google.ca/maps?hl=en&ie=...,0.022831&z=15

    Project page
    http://www.i-95expresstolllanes.com/.../i695_etl.aspx

    Personally if I was the city I'd wait on this idea, let some other cities prove if the concept works. I think for diamond interchanges the SPUI is probably the most efficient.

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    I don't think that the intersection above and this thread are really one and the same..

    Furthermore it seems like changes are being made to add things like toll roads and more lanes.

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    They're in the process of building one of these in Utah right now too.

    http://www.udot.utah.gov/pioneer/

    From what I understand, the big advantage is that you have less time lost in running the traffic lights - you only have two phases instead of the 4 you do on a SPUI (Single Point Urban Interchange), which is what would likely go in otherwise.

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    I imagine that something like this would have to clear hurdles with Alberta Transportation and Transport Canada. Still, it looks like an interesting design, and it might work with something like Fort Road/Yellowhead Trail.
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    round-a-bouts work just fine in the UK, even for highways.

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    Quote Originally Posted by etownboarder View Post
    Quote Originally Posted by RTA View Post
    That's actually quite interesting...I can think of several interchanges here that could benefit from this design (St. Albert Trail at Yellowhead Trail comes to mind).
    97 Street over the Yellowhead would be another good one.
    Why change an existing interchange? Apply the concept to an intersection that already in dire need of a new interchange, like Yellowhead and 127 St.
    “You have to dream big. If we want to be a little city, we dream small. If we want to be a big city, we dream big, and this is a big idea.” - Mayor Stephen Mandel, 02/22/2012

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    Traffic circles are great in low volume conditions and I'd like to see more of them (like replacing all of the 4-way stops with roundabouts). They don't work well at high volume though, they get monopolized by traffic in a single direction.

    As for the "diverging diamond", I don't think it could be built within the same footprint as a SPUI. The left turn ramps will need enough room for a reasonable turning radius as well as allowing for a weaving zone between them.

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    Quote Originally Posted by Sonic Death Monkey View Post
    Why change an existing interchange? Apply the concept to an intersection that already in dire need of a new interchange, like Yellowhead and 127 St.
    Building a whole new interchange costs big bucks, while modifying an existing interchange that is nearing or at capacity for left turns would be significantly less.

    Not that the Yellowhead couldn't use a few more interchanges, but that really is a different discussion from this one.
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    ^ I don't like the idea of spending money on an existing interchange that can be used for a new interchange.
    “You have to dream big. If we want to be a little city, we dream small. If we want to be a big city, we dream big, and this is a big idea.” - Mayor Stephen Mandel, 02/22/2012

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    I really don't think the cost of realigning roads and signals across an existing interchange is remotely comparable to building an entirely new one.
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    Actually in the UK they use two types of interchanges using traffic circles or roundabouts, one has two small roundabouts where the traffic lights would be, this works well for lower volume roads
    http://maps.google.com/?ie=UTF8&ll=5...,0.021243&z=16

    For more larger volumes they use a large traffic circle with two bridges, this would be a very similar concept to Whitemud 170th or Whitemud 111th
    http://maps.google.com/?ie=UTF8&ll=5...,0.042486&z=15

    For even larger volumes the cross road can be elevated over or sunken under. Personally I think the traffic circle concept is better than flipping the traffic over to the other side. The only advantage to flipping traffic would be where most of the traffic turns left.

  22. #22

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    Quote Originally Posted by sundance View Post
    There is (perhaps was now) an interchange in Baltimore where they did something similar having the lanes flip over, alas reality didn't work out quite so well, they are now in the process of rebuilding it.

    Old view;
    http://maps.google.ca/maps?hl=en&ie=...,0.022831&z=15

    Project page
    http://www.i-95expresstolllanes.com/.../i695_etl.aspx

    Personally if I was the city I'd wait on this idea, let some other cities prove if the concept works. I think for diamond interchanges the SPUI is probably the most efficient.
    Yeah I think people aren't realizing in the schematic above that the cars that are going "left" end up recovering on the wrong side of the road to facilitate this design which then requires a flip over at some point.
    People can't use traffic circles here. This would be a nightmare for the lowest common denominator driver.

    Keeping in mind also the quoted example in the link is a bridged overpass. So I fail to see how left turns are in issue in this anyway.. Stupid design.
    Last edited by Replacement; 26-11-2009 at 09:20 AM.

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    Darwinian selection will remove the people who can't use traffic circles.

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    Quote Originally Posted by Replacement View Post
    Yeah I think people aren't realizing in the schematic above that the cars that are going "left" end up recovering on the wrong side of the road to facilitate this design which then requires a flip over at some point.
    By "cars that are going left" you're meaning all the people who are forced to the left side, but who are actually going straight? What could possibly be wrong with throwing two chicanes into 97st? And two chicanes on St. Albert Trail would be a nice complement to the squarecircle at 118ave.

    So where would this actually work? It has to be somewhere where the straight-through traffic on the cross-street is tiny compared to the volume turning. Maybe 127st? Or out on one of the corners of the Henday somewhere? It's basically useless anywhere you have a real grid though.
    Last edited by newfangled; 26-11-2009 at 12:21 PM.

  25. #25

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    Here is another image of this type of intersection. It is not that new. The 'Diverging Diamond' has been in text books for more than a few years.

    Here is lots of information on this type and many others. You can view several dozen types and read detailed info on many of them. Remember to click the submit button after you make a selection. You can see animation of the intersections as well.

    http://attap.umd.edu/UAID_gss.php?UA...=22&iFeature=1
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  26. #26

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    More on traffic flow

    Here’s how self-driving cars could clear up traffic jams
    By Brad Plumer, Published: September 24

    This is a fun 23-minute presentation from Tom Vanderbilt on the often-bizarre psychology of driving and why traffic jams happen:

    http://www.washingtonpost.com/blogs/...-traffic-jams/


    I've posted this thought elsewhere on c2e (see below). The people that pass the lineup in the disapearing lane, then move over keep pushing back in the queue those already in the lane behind them.


    "We're all basically idiots when it comes to merging. Whenever a road shrinks from two lanes to one, it would actually be most efficient for everyone to stay in their lane right until the point where the lanes converge and then execute a "zipper merge." But most drivers feel bad about doing this and tend to shift over to the open lane early. This causes congestion."

    http://www.washingtonpost.com/blogs/...-traffic-jams/
    Last edited by KC; 24-09-2013 at 04:11 PM.

  27. #27

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    Quote Originally Posted by Edmonton PRT View Post
    Here is another image of this type of intersection. It is not that new. The 'Diverging Diamond' has been in text books for more than a few years.

    Here is lots of information on this type and many others. You can view several dozen types and read detailed info on many of them. Remember to click the submit button after you make a selection. You can see animation of the intersections as well.

    http://attap.umd.edu/UAID_gss.php?UA...=22&iFeature=1
    bumped



    Canada’s first ‘diverging diamond interchange’ now open to Calgary traffic

    http://globalnews.ca/news/3667111/ca...lgary-traffic/
    The project is Canada’s first Diverging Diamond Interchange, and the city acknowledges it may seem strange for some drivers at first. While travelling through the interchange, traffic crosses briefly onto the opposite side of Macleod Trail.

    “The only weird thing about it is there’s an intersection on either side and when you cross through the intersection onto the green, you very briefly end up driving on the left side of the road, so you feel like you’re in England,” Calgary Mayor Naheed Nenshi said.


    The city has produced the following animation to help explain how the interchange works.
    There are a bunch of them in Salt Lake City and they work very well IMHO
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  28. #28

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    Still not sold on it. It still looks like a detour. A question is how those new to the interchange, and never having engaged it before would fare in this exchange in standard winter conditions when the lane markings are covered. Which leads me to wonder what lane recovery will look like even if drivers figure out where the hell to be going on that road.

    Make it clover leaf, KISS. Sometimes the simplest designs and solutions are the best ones.

    All that said these appear to have their use in interchanges that involve quite a lot of left turns. I can see little argument for these if there is not a substantial amount of lefts in an area, but still dealt with better by a flyover lane or underpass lane.

    I'd like to see the relative costs of the respective designs. I doubt this one saved money.
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  29. #29

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    If clover leaf worked we wouldn't be abandoning them en masse.
    "Men never do evil so completely and cheerfully as when they do it from religious conviction" - Blaise Pascal

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    Pfft. It'd have worked just fine in Calgary if the City had the moxie to do it the old fashioned way & the endless money it'd require to buy out the massive amount of already-developed land! You're just thinking inside the box, Chmilz
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    Problem with cloverleafs, of which they had many when I lived in Calgary, is that you have traffic trying to accelerate up to speed in the same lane as traffic is decelerating to exit.

    Brake shops love them!
    ... gobsmacked

  32. #32

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    That, and they take a huge amount of space and are extremely dangerous to traverse without a car.
    There can only be one.

  33. #33

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    Quote Originally Posted by McBoo View Post
    Problem with cloverleafs, of which they had many when I lived in Calgary, is that you have traffic trying to accelerate up to speed in the same lane as traffic is decelerating to exit.

    Brake shops love them!
    Cloverleafs were designed and used even at a time where acceleration and braking and handling were more limited in vehicles. Todays vehicles should be able to handle these easier. I have no trouble maintaining sufficient speed in a cloverleaf and accelerating to merge. Also no trouble observing what I am merging into.

    The beauty of Cloverleafs are they are relatively less intensive engineering wise. They don't require intense construction or cost.

    The land and taking up space comment is a red herring in most situations, plus this is Canada, we have a lot of land. Compression of roadways due to competing land use is not typically an issue here.

    In anycase how much less space is the Traffic Flow through pattern typically taking?
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    Quote Originally Posted by Replacement View Post
    Cloverleafs were designed and used even at a time where acceleration and braking and handling were more limited in vehicles. Todays vehicles should be able to handle these easier. I have no trouble maintaining sufficient speed in a cloverleaf and accelerating to merge. Also no trouble observing what I am merging into.
    This is hilarious to me, since I remember you blaming all sorts of things (except yourself) for your inability to stay within the speed limits. You're a merge master but lack the ability to see speed limit signs or accurately manage the speed of your vehicle, interesting.

    Quote Originally Posted by Replacement View Post
    The beauty of Cloverleafs are they are relatively less intensive engineering wise. They don't require intense construction or cost.
    Except for the land. Oh, wait, you've got more to say about land:

    Quote Originally Posted by Replacement View Post
    The land and taking up space comment is a red herring in most situations, plus this is Canada, we have a lot of land. Compression of roadways due to competing land use is not typically an issue here.
    Except in this case there's been development there for years, which you're conveniently forgetting as you move the goalposts at fevered speeds.
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  35. #35

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    ^What on Earth are you yabbering about? The discussion is about "New Traffic flow pattern" it is not specifically about the Calgary interchange. People are discussing this concept with ideas around Edmonton use application. My comments are consistent with that. Typically in interchanges land is not an issue. Usually the main roadway or freeway has sufficient land use allocation for differential design.
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    Quote Originally Posted by Highlander II View Post
    That, and they take a huge amount of space and are extremely dangerous to traverse without a car.
    Actually, the design has safer pedestrian ways than cloverleafs.
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  37. #37

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    Try it, you will like it. I drove through one, at least twice every day in Salt Lake City for 3 months.

    They are way better than many other forms of interchange with lights. Remember, this is not a full free flow replacement for a large cloverleaf interchange but a replacement for conventional diamond interchanges and high volume at-grade intersections.

    Here are some points
    "The diverging diamond interchange was listed by Popular Sciencemagazine as one of the best innovations in 2009 (engineering category) in "Best of What's New 2009""

    Studies show that the design have consistently proven to reduce accidents and increase traffic volumes with less delays.

    Safety Benefits
    Fewer conflict points (14 for DDI, 26 for conventional)
    Conflict points spread out throughout interchange
    Better sight distance at turns
    Virtually no driver confusion (FHWA study and new DDI observations in Springfield, MO)
    Traffic calming features when desired
    Wrong way entry to ramps extremely difficult
    Pedestrian crossings are shorter

    Supporting Data
    MODOT survey shows that 97% of drivers feel safer in the new Springfield DDI compared to the previous diamond interchange
    Crash data for the new Springfield DDI show a 60% reduction in collisions in a five-month comparison of the old interchange
    Versailles, France DDI showed that within a five-year time span that was examined, there were only been 11 reported light crashes
    Operational Benefits


    Unique phase combinations
    “Free” or simple left and right turns from all directions
    Increases left turn lane capacity without needing more lanes
    Only two phases needed, shorter cycle length
    Lanes with multiple assignments in all directions
    Better storage between the ramp terminals
    More functional during a power outage
    U-turns from highway are accommodated well
    Better signal network synchronization
    Supporting Data


    MODOT survey shows that 95% of drivers felt that there was less congestion in the new Springfield DDI compared to the previous diamond interchange
    Daily traffic backups that sometimes had over a mile queue were completed eliminated once the construction of the new Springfield DDI was complete.
    Cost Benefits


    For a retrofit
    Existing bridge can usually be used
    Additional right-of-way rarely needed
    Construction time is reduced
    Maintenance of traffic is simplified during construction

    For a new interchange

    Fewer lanes than other interchange forms
    Less bridge structure
    Less right-of-way than a cloverleaf form

    http://www.divergingdiamond.com/benefits.html
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    I would imagine those studies have taken place mostly in non winter climates. Requiring people to lane position multiple times and including on the wrong side of the road does not seem like an innately great idea for a winter climate. That said I would have to experience it in winter conditions to know one way or the other.

    In anycase when discussing these things its not my personal preference that I am engaged in its a realization of the need to KISS regarding our collective driving population which contains drivers that hit stationary objects more than any jurisdiction I am aware of.

    Where would you think such an exchange is required, or should be tried in Edmonton area?
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  39. #39

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    Quote Originally Posted by Replacement View Post
    I would imagine those studies have taken place mostly in non winter climates. Requiring people to lane position multiple times and including on the wrong side of the road does not seem like an innately great idea for a winter climate. That said I would have to experience it in winter conditions to know one way or the other.

    In anycase when discussing these things its not my personal preference that I am engaged in its a realization of the need to KISS regarding our collective driving population which contains drivers that hit stationary objects more than any jurisdiction I am aware of.

    Where would you think such an exchange is required, or should be tried in Edmonton area?
    So you basically swap sides on the overpass and then return to the normal side. Seems that they could have raised one direction of travel higher and added a couple overpasses for it on either side of the bridge to eliminate those two criss-cross intersections.

    Also it seems somewhat like a reversing traffic circle, without the circle's advantage of eliminating oncoming traffic intersections.
    Last edited by KC; 15-08-2017 at 03:37 PM.

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    Might not be current now that planning is well underway to upgrade Yellowhead to full freeway status, but at one time there was a plan for a diverging diamond at Yellowhead and Fort Road.
    ... gobsmacked

  41. #41

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    ^ That was still the plan last I heard.

    ^^ That's called a DCMI. http://www.dcmiinterchange.com None have been built anywhere, but it's a good concept. $$$ for the extra bridges though.

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    Cloverleafs (leaves?) work well in moderate traffic situations, they can work better if you separate the ramps from the main traffic flow with collector/distributor (c/d) lanes, such as on Whitemud and AHD east.

    Folded cloverleaf, or folded diamonds (AHD east/Baseline and others) can handle more traffic.

    To handle to most traffic you can only have at most 1 loop ramp per side, AHD Yellowhead west for example, and about the only thing more you can more lanes to the mainline flow and relevant ramps.

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