Diverging Diamond: Lots of Press First Day

First morning of the Ashford Dunwoody Divering Diamond

It seems that things were successful today, the first full working day of the Ashford Dunwoody Diverging Diamond.

I was out for the evening rush hour, and with all the caveats that come with “it’ll take a few days to tweak the signals” things worked well. The queues on Ashford Dunwoody cleared very quickly and there was little or no confusion that I observed. There was some backup on the eastbound off ramps that affected the interstate, but I have high hopes that the aforementioned signal tweaks will alleviate that in the future. The backup was a transient event that was caused by the high volumes of traffic that use the Ashford Dunwoody off ramp. It’s a well known traffic engineering principle that after a certain volume of vehicles, traffic “quality” becomes unstable, and can be disrupted by very small events. The disruption can take a long time to clear, and can occur very quickly. For example, here is a picture of the congested off ramp, about 20 minutes before it locked up.

The new eastbound off ramp for the Ashford Dunwoody divering diamond

It was working great at 5:05 PM and then it went kerplooie for a while. Unfortunately, that happens, but some very good engineers were on hand to adjust and work with it.

As the title of the post says, there was a lot of press coverage today. Just a sample is:

Atlanta Journal Constitution: Commuters Survive Opening Day at New Interchange
CBS Atlanta
NBC Atlanta

I call your attention specifically to the AJC article. There’s a reference in there that I will quote in full, to emphasize that construction is not complete yet:

Mark Rackin said work on the project added 10 minutes to his commute by eliminating the dedicated right-turn lane onto Lake Hearn Drive where he works. Monday’s opening, he said, cost him another 10 minutes.

“When I heard all the hoopla Sunday afternoon, I knew what was coming and dreaded today’s drive,” he said. “I was right; it was the worst ever.”

The dedicated right turn lane to Lake Hearn Drive is likely to remain closed for a while, but it’s been closed for at least a month before this. What caused the congestion being referred to is that the right turns onto Ashford Dunwoody are now controlled by right turn arrows, which are red while the southbound Ashford Dunwoody traffic is moving.

Right turn arrows for the east to south turning movement off the I-285 off ramp

These arrows indicate that you are not supposed to turn on red1 which is different than the previous movement which allowed for right turns on red.

There is light at the end of that tunnel, though. As soon as the “slip ramp” from the off ramp directly to Lake Hearn Drive is opened, the congestion referred to in the quote will vanish. There is still work to do, though, shown here.

The yet-to-be-completed Lake Hearn Drive slip ramp

It’s looking great and I’m very excited to see it working. I’ll be more excited once the “splitter islands” are in place rather than being outlined by barrels. I’ll be even more excited than that once the median island is constructed and pedestrians can start using it, but that is another post.

  1. Actually, my Georgia Code knowledge is abandoning me here; I’m not sure you cannot turn on a red arrow if there is no attendant “NO RIGHT TURN ON RED” sign. I’ll look that up later. []
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