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John Ruch Posted by on December 13, 2016.

Abernathy tunnel is among bike/walking-friendly ideas for 285/400 project

Advocates are pushing for better bicycle and pedestrian facilities on Sandy Springs streets altered by the upcoming I-285/Ga. 400 rebuild project—with at least bike lanes, and possibly bike/pedestrian tunnels under highway ramps on Abernathy Road.

Joe Seconder of Georgia Bikes raised the tunnel idea in a Dec. 6 meeting with Georgia Department of Transportation officials—including 285/400 project manager Butch Welch—and he says they were willing to think it over. It’s a big idea, but there is precedent in GDOT already agreeing to build part of the PATH400 multi-use trail through the interchange, also a request by Seconder’s group and other advocates. But the clock is ticking, as GDOT’s contractors are slated to finalize design and start construction in February.

The existing diverging diamond interchange at Ashford-Dunwoody Road and I-285 in Dunwoody, from the Perimeter Center Improvement Districts website.

The existing diverging diamond interchange at Ashford-Dunwoody Road and I-285 in Brookhaven and Dunwoody, from the Perimeter Center Improvement Districts website.

“The idea is definitely, Who has the priority? What is the greater safety for everyone?” said Seconder.

Officials from GDOT and other organizations involved in street-planning, including the Perimeter Center Improvement Districts and the city of Sandy Springs, did not have immediate comment.

While the 285/400 project is largely about those highways, it also affects some city streets and its work actually will start, in February, with two of them in Sandy Springs. One is a reconstruction of the Mount Vernon Highway bridge over 400. The other is reconstruction the Abernathy/400 intersection into a “diverging diamond interchange,” where traffic switches to the other side of the road between traffic signals to speed vehicle flow around highway ramps.

Diverging diamonds are a new concept; an early local model, built in 2012, is the Ashford-Dunwoody Road/285 interchange between Brookhaven and Dunwoody. That Ashford-Dunwoody diverging diamond is on a bridge over the highway; the Abernathy version will go beneath a highway overpass.

The rough plan for two tunnels (yellow arrows) and a side path (green arrow) in the forthcoming Abernathy Road/Ga. 400 diverging diamond interchange as shown on Joe Seconder's Bike Walk Dunwoody blog page.

The rough plan for two tunnels (yellow arrows) and a side path (green arrow) in the forthcoming Abernathy Road/Ga. 400 diverging diamond interchange as shown on Joe Seconder’s Bike Walk Dunwoody blog page.

For two years, bike and pedestrian advocates have met with GDOT about better accommodations on those streets. Joining Seconder in recent meetings was Bob Dallas, a Dunwoody resident who chairs the Atlanta-based pedestrian advocacy group PEDS. Seconder noted that GDOT has a “Complete Streets” policy requiring many non-highway projects to accommodate all types of roadway users.

Seconder and Dallas said GDOT agreed to one basic request: 5-foot bike lanes on the Mount Vernon bridge. GDOT is considering their further request to separate the bike lane from vehicle lanes with some type of amenity ranging from reflective bumps to plantings or a low curb, Dallas and Seconder said.

The Abernathy diverging diamond has bigger challenges. Seconder said the current plans lack any bike lanes and have an unusual pedestrian crossing: two separate lights to cross the ramps, with pedestrians then walking on a median before making a double-crossing to exit again. The current Ashford-Dunwoody diverging diamond has the same set up, and Seconder says it can scare or discourage cyclists and pedestrians.

“We don’t see pedestrians walking across Ashford-Dunwoody…It’s just not a friendly, inviting place,” Seconder said.

Dallas isn’t as critical—“it’s OK,” he says of the Ashford-Dunwoody interchange—but agrees that it can be difficult for first-time users to understand and looks like it would take longer to cross than it does.

A pedestrian's-eye view of the Ashford-Dunwoody diverging diamond from the median sidewalk. Crosswalks branch out at sharp angles to cross the highway ramps via two islands. (Photo John Ruch)

A pedestrian’s-eye view of the Ashford-Dunwoody diverging diamond from the median walkway. Crosswalks branch out at sharp angles to cross the highway ramps via two islands. (Photo John Ruch)

A recent Reporter visit found the pedestrian crossing at Ashford-Dunwoody to take less than three minutes. Less attractive were damaged street signs that indicated that cars frequently drive onto the pedestrian islands that are part of the system.

Seconder and Dallas said their basic request for the Abernathy diamond is adding 5-foot bike lanes. That will be safer for “experienced” cyclists, Seconder says. But it could still discourage everyday commuters, he said.

Late in the Dec. 6 meeting, Seconder tossed out a new idea he has seen in other states: tunnels under the 400 ramps that would allow bikes and pedestrians to pass alongside the interchange instead of having to taking the twisting path through it. He said GDOT officials did not dismiss the idea.

“They said, ‘Let us know. We got a couple months,’” he said.

What they wanted to know about was cost and feasibility. Seconder said he got a rough estimate from the PATH Foundation, which funds multi-use trails, for $7,000 per linear foot to build such tunnels, which would mean millions of dollars for two, 200-foot segments under the ramps.

A highway sign was apparently damaged by a vehicle driving onto a pedestrian island in the Ashford-Dunwoody diverging diamond. (Photo John Ruch)

A highway sign was apparently damaged by a vehicle driving onto a pedestrian island in the Ashford-Dunwoody diverging diamond. (Photo John Ruch)

But Seconder believes local corporations whose employees would benefit from easier commuting via the nearby Sandy Springs MARTA Station might be willing to pony up funds.

Dallas said the tunnels are an “intriguing idea.” He cautioned that cost and right of way could be major challenges.

But he also noted that all current Perimeter Center planning is “very pedestrian-focused,” and the 285/400 projects are“50-year improvements that will be here long past when we’re gone.”

“The Abernathy interchange is a very key one,” Dallas said, noting that Mercedes-Benz USA is building its new headquarters along Abernathy in part due to that MARTA access. For that reason, “pedestrian and cycling improvements ought to be of the highest order” in that area, he said.

For more about Seconder’s tunnel proposal, see his blog post here.

One Response to Abernathy tunnel is among bike/walking-friendly ideas for 285/400 project

  1. Scooter Boy

    December 16, 2016 at 7:58 am

    This will be a “Toll Route” like is happening on the highways around us right?

    IF a minority of people want an expensive piece of infrastructure for their convenience they should be willing to pay for it. Put gates at either end and require a fee to open them.