Georgia’s First Diverging Diamond Opens Monday

We’ve blogged about diverging diamond interchanges before (see here, here, and here). Now we’ll get our first chance to use one on the I-285 @ Ashford-Dunwoody Rd. bridge. The AJC has a write up:

The Perimeter CIDs initiated the DDI project in 2009 when they spent $100,000 to hire an engineering firm to find an interim solution to backups at the interchange. The PCIDs secured funding for project design and engineering from the State Road and Tollway Authority and DeKalb County. That projected cost to date totals $824,423. GDOT is funding the $4.6 million cost of the DDI construction.

That same year, Missouri built the first diverging diamond, and it has proved to be a big hit, said Don Saiko, a project manager for the Missouri Department of Transportation.

After the first interchange opened in Springfield, four more were quickly added. An additional half dozen are either under construction or in the planning stages.

Saiko said backups at the Springfield interchange on I-44 would sometimes reach three miles. Now, he said, there are no backups.

Also this video:


  1. View from Brookhaven says:

    Well, I should probably enjoy my last weekend on this planet. Because I will surely perish around 7:30 on Monday morning…

    • Dave Bearse says:

      I would of thought a small government libertarian would prefer a modest two year $4.6M improvement to a big government two decade $46M (or much more) solution.

      I oppose T-SPLOST for reasons very different from yours. However like like the Bartow County Tea Party leader voicing opposition to T-SPLOST because her gas taxes were already funding MARTA, influencing of those that haven’t made up their minds is undermined by categorical opposition to any taxation to fund transportation.

      • That depends on what you get for the money…. $4.6 million for a little asphalt, traffic lights and new paint job just reminds me of the DOD paying $150 for hammers and $500 for toilet seats.

  2. peachstealth says:

    Other than not taking as much land, how is this better than a cloverleaf?

    Perhaps that would work in Macon at I-16 and Spring Street where the interstate is too close to the river for a cloverleaf.

    • Dave Bearse says:

      Other than not taking as much land, how is this better than a cloverleaf? $4.6M and completed in a year, versus many tens of millions, and completed a decade later.

      • The Last Democrat in Georgia says:

        “$4.6M and completed in a year, versus many tens of millions, and completed a decade later.”

        Try close to $200 million and completion close to TWO decades later.

        From the link to the AJC article that Buzz provided above:

        “Yvonne Williams, the president and chief executive officer of the Perimeter CIDs, said any hope of improving the intersection through normal means would have been far in the future. That plan, according to GDOT, calls for a complete reconfiguration of the bridge at an estimated cost of $170 million, including construction and right of way. Such work could not be scheduled until at least 2030.”

        • Dave Bearse says:

          I knew the $46M was low-ball, but it and the time frame were complementary 10 times more.

          • The Last Democrat in Georgia says:

            The talk of waiting at least 20 years to make pressing infrastructure improvements makes me think that this town is totally screwed.

            There seems to be very little sense-of-urgency to address the traffic and perception issues that are a problem NOW that should have been addressed many, many years ago.

          • The Last Democrat in Georgia says:

            But, hey, I guess that the Diverging Diamonds at I-285/Ashford-Dunwoody, I-85/Pleasant Hill and I-85/Jimmy Carter are better than the absolutely nothing that we would’ve gotten otherwise, despite the pressing need.

  3. rrrrr says:

    Because it lets you drive on the “WRONG” side of the road and release your “inner” Brit.

    TEA anyone?

  4. Direct Diamond Interchange (“DDI”) is a great concept. This design moves traffic much quicker than traditional bridges.

    The Gwinnett Place Community Improvement District and Gwinnett County are replacing the bridge at Pleasant Hill Road over I-85 with a Direct Diamond Interchange at Pleasant Hill., with construction about to start. Pleasant Hill Road and bridge are among the most congested in Gwinnett County and the new DDI there is going to greatly relieve traffic, too.

  5. Bridget says:

    I just did the Ash-Dun detour about an hour ago. Yes, they’re working today, but I just can’t see any way this thing will be ready for use by Monday. Maybe NEXT Monday…

    • The Last Democrat in Georgia says:

      That new interchange looks like someone from the cast of the stoner movie “Friday” designed it.

      But if it works, I promise to personally go down to the State Capitol and get the boys (and girls?) at GDOT another big bag of what is obviously their favorite brain stimulant.

      And if it doesn’t work, I promise to personally heap more scorn on an agency and state government that has seemingly been increasingly more than deserving of it as of late.

        • The Last Democrat in Georgia says:


          I think that you misunderstood. I wasn’t talking about GDOT being down at the State Capitol.

          I was talking about if the new design works, personally rewarding GDOT with another big bag of their favorite “brain stimulant” which is often bought and sold (and seemingly often used) in the area (in and) around the State Capitol if you know what I mean, seeing as though the design of that new interchange clearly had to have been thought up while in an altered state…

          But, hey, whatever helps traffic move better.

      • LDIG,

        On behalf of the commuters who use those roads, please stay away from the area. Your seething rage will no doubt cause accidents and damage to property and life.

        • The Last Democrat in Georgia says:

          Me?…Road rage?….No way!

          I don’t know what could’ve possibly ever given you that impression?

  6. Tiberius says:

    Boy, this driving on the left is going to confuse the hell out of some people.

    Looks great though. Look forward to seeing it live.

  7. saltycracker says:

    It is intended for the alert, law compliant but..Atlantans….obeying traffic signals…..really ?
    Hope they have those ticket cameras installed so we can get this paid for quickly.

  8. GTKay says:

    The interchange will be open, but I don’t believe all the lanes will be open yet. Also, I imagine the media will be there with their trucks and three-story antennae and people hanging out at the edge of the road with microphones like they were when the 400 emergency lanes opened. So keep that in mind if it turns out to be a less-than-flawless first day.

      • The Last Democrat in Georgia says:

        Come on, Buzz, you know that I’ll give it more than one day to work before I declare it a total disaster.

        …We should know whether or not it is a complete failure by no later than noon of the second day.

        …I’ve got GDOT’s number on speed dial to give them a piece of my mind if everything hasn’t quite panned out by then.

  9. Max Power says:

    I can’t wait to see how this functions the first time the traffic lights are out.

  10. seenbetrdayz says:

    I’d at least find a cop brave enough to stand in the middle of the intersections to make sure folks don’t keep to the right when they’re supposed to switch to the left.

    I like the concept, though. But, much like anything else, it’s going to take some getting used to. That goes with any major changes in a daily commute, though. There’s nothing more thrilling than realizing the intersection you’ve been driving through for a year on the way to work suddenly had been converted to a four-way stop a week ago, and you just now noticed the new stop signs.

    • saltycracker says:

      it cost $5.5 million (more than est. but a fraction of a cloverleaf) – we’d better hope it works and works well…

  11. GTKay says:

    Well, based on the absence of horror reports coming out of the media, the DDI seemed to have a successful morning commute. The AJC did dutifully find someone who complained that it added to her commute, but good news seems to be no news over there. Sorry to disappoint, but we still have the evening rush hour. And there’s always tomorrow.

      • bgsmallz says:

        Not that anyone cares what I think, but I think it might be a solid concept. You can really tell the difference b/w the old set up and the new set up in the amount of time that is cut down by removing some of the light cycles. I’ll be happy to see the final product (I’m still waiting to see how in the world they make a center island safe for pedestrians…it will certainly be an upgrade regardless. It didn’t take too many times crossing the on-ramp to 285 without a crosswalk to realize I needed to find a different jogging route…pedestrian traffic there is somewhat minimal, but I do see folks who are staying in the hotels trying to traverse there somewhat regularly). The real test will be when school is back in and A-D is clogged going southbound due to Marist traffic.

        Sorry…I’m sure that is TMI.

  12. DavidTC says:

    Heh, that looks like an intersection I came up with at some point. It would work exactly like this, but the premise was that there would be two cross bridges, but arranged vertically, one over the other. Which would keep anyone from having to stop at all, in any direction. The downside, of course, is that it would be rather more expensive. (OTOH, you’re building two bridges _anyway_.)

    But this seems a nice compromise, once people stop freaking out about being on the wrong side of the road. I especially like how one side fills up from the off-ramp while the other side is cutting across. I hope there’s some sort of ‘left-on-red’ option there if you end up at an off-ramp wanting to go left and there’s no oncoming traffic. I know generally left-on-red is allowed at one-way roads like this, but I hope there’s some sort of message, because a lot of people don’t know it.

    • John Vestal says:

      The solution to the “left-on-red” issue is already in use in a few spots up here in the northern ‘burbs…..the “flashing yellow arrow”.

      • bgsmallz says:

        The “turn on red” options aren’t clearly marked yet. In fact, that has been my only complaint. I was waiting to turn right on A-D road from the off ramp and I couldn’t tell if I could proceed when clear or if I needed to wait for a green arrow.

        • bgsmallz says:

          If anyone cares, they put in “No Turn on Red” signs signifying that you can’t make a right hand turn on red at the intersection. It makes sense as you probably would end up making guesses as to what the oncoming zig-zaging traffic is doing.

          Also, the middle of the road pedestrian walkway is rounding into form. It looks to be a large sidewalk ‘tunnel’ with 4 foot walls on each side. A bit intimidating to have traffic on both sides of you…but better than the old sidewalk with no cross walks.

          That should qualify in the ‘most mundane’ comments made on PP contest.

  13. Charlie says:

    This has generally been a non-news event since Monday morning.

    Does that mean it’s working?

    Anyone driven it late this week?

    • bgsmallz says:

      It seems like it is. I think it’s cut 3-5 minutes off my commute in the mornings. I used to have to wait 2-3 light cycles (not the kind from Tron) before turning left on 285 W…now it’s only 1.

      I’m commuting away from Perimeter, so my route is probably in the minority. It’d be worth hearing from someone that actually commutes to Perimeter rather than lives near there.

      I haven’t seen any accidents and also noticed yesterday afternoon that the police officers that they used to have stationed on the bridge (even before the construction) are gone.

    • Rambler1414 says:

      I was there Wednesday around lunchtime. It’s working fairly well.

      Note: The interchange is still under construction. All they did Monday was officially flip the traffic. All of the temporary signs and temporary striping are still in place. None of the new signals or raised islands are in place. It’ll take a couple of more months for it to be 10)% complete.

      As someone posted above, the true test (like 400 shoulders) will be in September when schools are back in. Traffic always drops during the summer months.

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