Gwinnett Boasts New “Diverging Diamond” Interchanges
Decatur Metro | September 8, 2011
Al points to this article in the AJC, which is sure to interest the more transportation-obsessed among us. Gwinnett plans to unveil a new “diverging diamond” at the busy intersection of I-85 and Jimmy Carter Blvd, with similar designs coming to other major county intersections in the coming months and year.
The unusual design, known as a DDI, routes traffic in both directions to the left over an interchange bridge, so that the lanes are briefly reversed. That allows cars turning left onto the interstate ramp to do so without facing oncoming traffic. Cars coming off the interstate also can merge more easily with traffic, designers say.
Not only do designers and advocates believe that the diverging diamond will improve traffic congestion, but that they will replace the county’s old watertowers as the “new symbol for Gwinnett”. The project is projected to cost no more than $750,000.
Huh.
Rendering above courtesy of New York DOT website
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Great for the traffic entering and leaving the interstate. Exciting for the through traffic. People get worked up enough about rotaries, how will they react to this?
What that needs is a couple of good sharrows.
This is the same thing that’s going to be done at Ashford-Dunwoody and I-285.
The Diverging Diamond demonstrates how creative engineering can help sprawl process even more cars than it already does. That makes them interesting from an innovation standpoint but they’re for cars, not for people. From a pedestrian or cyclist perspective, they’re terrible, oversized, hostile, unwalkable places. Gwinnett can have ‘em.
Well, to be fair, how many people are walking or biking at the intersection of 85 and Jimmy Carter?
It’s an area that’s heavily populated with immigrants, so my guess is that there are lots of people walking and biking.
walking and biking
i;ve ridden a bike through there a couple of times
pretty vivid experience!
wle
I see very clear crosswalks and paths in this depiction. To suggest that we should not make an interchange like this less congested because of pedestrian and cyclists is just silly in my opinion.
Uh, who said that? All I said is that they’re best suited to a particular use — processing more cars. How does that suggest it shouldn’t be built? It only suggests it’s a context-specific solution and shouldn’t be built where pedestrian and bicycle mobility is valued and prioritized.
“Gwinnett can have ‘em.”
____________
Seemed clear to me.
“shouldn’t be built where pedestrian and bicycle mobility is valued and prioritized.”
________________________
Just don’t see how this is a problem for pedestrians and cyclists.
For gwinnett’s golf-ball sized consciousness, this is progress. Solution? Two words: commuter rail.
If this thing were the symbol for my hometown, I would be so sad.
+1
Me too. Oh wait, I am from Gwinnett County. Sad, but happy to have moved to Decatur!
No more than 750k? HIGHLY doubt that figure.
Thats what I thinking.
We have drivers that can’t figure out a roundabout or sharrow so I’m sure this design will be smoothly adopted without incident….I’ll get the popcorn…
Just because we can, doesn’t mean we should.
Looking at that gave me an instant migraine. Thanks, DM.
I’m with you, Lump. It took me a while to figure it out and I’m not even drunk. Heck, sober + driving would be a challenge on that thing.
Looking at that all I can think of is We’re All Going To Die!
I think it’s great. There’s even sidewalks and crosswalks so that people can park at the Bass Pro Shop on the near side and take a leisurely stroll to the Cracker Barrel on the far side. Ahhhh, Paris!
This would be a great idea for the Memorial @ I-285 interchange.
Today, the traffic turning left onto the interstate in both directions tends to get stuck in the middle of the intersections, sometimes causing double blockage. This would avoid that scenario.
I’m really frightened by all of you who think this is confusing. My blood pressure will be up driving home today knowing you all are out on the road with me…
Your world frightens and confuses me! Sometimes the honking horns of your traffic make me want to get out of my BMW.. and run off into the hills, or wherever..
Ingenious design. Similar to a traffic circle in that it keeps traffic moving. Hope it works. Now, can someone come with a good traffic design for crossing train tracks??
It’s called a bridge.
A highway interchange as a symbol for Gwinnett? Sounds appropriate enough.
Dear Snark Patrol-
In fact, moving the cars that are using that intersection through more quickly reduces their idling time which reduces carbon emissions and wasted gas.
The intersection at I-285 and Ashford Dunwoody will be the first of its kind in the state. I’m certain several Decaturites will appreciate that as they use ADR and Clairmont/Clairemont to bypass 285 to get to Perimeter. (Some people in Decatur drive…gasp!) (Although…the Clifton Corridor would actually make transit from Decatur to the PCID a viable option..fingers crossed.)
Anyway, as a former Decatur resident who now lives close to the 285-Ashford Dunwoody intersection, I can report that there are no functioning crosswalks at this intersection, the two right hand entry ramps to 285 on the SB side create a huge mess. So as for the comment…”From a pedestrian or cyclist perspective, they’re terrible, oversized, hostile, unwalkable places”…that’s really relative, you dig?
As far as the $750K price tag…this article states the Ash-Dun DDI will be closer to $8M.
http://www.thecrier.net/article_ed8eb741-0873-553a-a0a6-f5da23a452a1.html
It’s not relative. It’s a fair assessment in any context, even if a DD represents some modest improvement over what’s there now. What’s relative is when an auto-focused solution such as the DD might be appropriate. As I said before, they process more cars more efficiently. They represent innovation if that’s the problem you’re trying to solve, and the spot in Gwinnett or the spot you mention may be perfectly reasonable candidates. That’s for their respective communities to decide.
But that doesn’t make their infrastructure any friendlier to peds or bikes so, if the mobility of those folks is one of your community priorities, DDs are likely not the tool you want to use.
You’re right…if there were no sidewalks and to cross the street I had to use a vine to swing over a lake filled with crocodiles just like in Pitfall, the diverging diamond would still be a terrible idea.
Terrible, over sized, hostile, and unwalkable…none of those words invite any sort of relative comparison…riiiiiiiiiiiight.
Anyway, the DDI is ‘auto focused’…but it doesn’t mean it craps on the needs of pedestrians or can only be a ‘modest’ improvement. Just because they aren’t burning down the ramps to 285 and replacing the bridge with a single lane roadway surrounded by Elysian fields doesn’t mean it can’t be pedestrian friendly. Somewhere in the world, there will be busy roads…I think they can coexist with pedestrians if we try.
Wide sidewalks, clearer traffic signals, marked/upgraded/working cross walks, and new trees are all a part of the design to incorporate that corridor with the other many pedestrian improvements throughout the PCID.
As far as the loaded statement about ‘community priorities’…well, Decatur in itself doesn’t have to make many choices about intersections with interstates and that has nothing to do with community priorities. Anyway, a good example would be improvements at Scott-NDR-Medlock…I can tell you that crossing that intersection has never been a good idea. I’m still not sure how I survived the bike rides from Glennwood Estates to Medlock Park. If traffic improvements were made at that intersection, it would probably be ‘auto-focused’, but I imagine it would still result in a much more friendly ped environment.
One last note and I’ll leave with this…the AJC, as usual, missed the boat. Note this ‘small detail’ of why some Gwineetians are envisioning this a a symbol for the area.
http://www.bizjournals.com/atlanta/news/2011/09/09/bridge-to-provide-new-gateway-to.html
Will they dress up the existing bridge? The TIA project for a new bridge on Jimmy Carter Blvd at I-85 did not make the unconstrained list. I think the existing, seven lane bridge is wide enough for a six lane DDI.
They would be much better off making double-roundabout diamond interchanges.
The interstate would still pass over or under the surface street but the intersections between the ramps and the surface street would happen at roundabouts instead of standard intersections or this DDI mess.
See: http://maps.google.com/maps?q=vail,+colorado&hl=en&ll=39.644139,-106.377879&spn=0.004759,0.009645&sll=37.0625,-95.677068&sspn=40.001301,79.013672&vpsrc=6&t=h&z=17 and http://maps.google.com/maps?q=vail,+colorado&hl=en&ll=39.6279,-106.420586&spn=0.00238,0.004823&sll=37.0625,-95.677068&sspn=40.001301,79.013672&vpsrc=6&t=h&z=18
Understand the skepticism regarding the $750K price-tag. That cost only relates to the architectural component (which the CID is covering). The County is paying for the actual DDI reconfiguration (the cost for that is in the neighborhood of $4M.
Regarding the pedestrian component, the new design will be much more pedestrian friendly than the current layout. If you’ve ever been on that interchange you know that it is actually a bit scary to walk across. In an ideal world we would be building 15 foot sidewalks, but we have to work with current footprint of the bridge (replacing it is about another $80M).