Georgia’s first diverging diamond — one year later

As Gwinnett County welcomes two newly redesigned interchanges, Dunwoody is celebrating the one-year anniversary of its diverging diamond at I-285 and Ashford Dunwoody Road. State and local officials spent three years and more than $6 million on the redesign that opened a year ago this month, the first of its kind in Georgia.

Early numbers show the design reduced travel times and decreased accidents at the busy interchange that sees more than 55,000 vehicles a day.

What commuters say:

"I take it every day, and so far, yes, I like it. It frees the left lanes over the bridge." -- Hugo Guerra, Dunwoody

"I don't use it every day, but it's like anywhere in Atlanta with traffic — try to avoid it at certain times of the day." -- Michael Wolters, Sandy Springs

Some of the costs:

$4.6 million: Georgia DOT construction contract to E.R. Snell Contractors of Snellville

$100,000: Perimeter Community Improvement Districts contract for design work

$800,000: Grant through the State Road and Tollway Authority

$450,000: DeKalb County HOST funds for design and engineering

$300,000: Perimeter CID landscaping

The new commute:

Total travel time decreased by about 20 percent, and total stopped time (time spent under 5 mph) decreased by about 50 percent.

Travel statistics between Lake Hearn Drive and Ravinia average in both directions a distance of about 0.45 miles.

Morning drive Avg. time Avg. # stops Avg. speed Avg. stopped time
April 2012 1.86 min. 1.59 18.71 mph 0.86 min.
April 2013 1.43 min. 1.45 20.55 mph 0.31 min.
  -23% -9% 10% -64%
Evening drive Avg. time Avg. # stops Avg. speed Avg. stopped time
April 2012 2.58 min.
2.30 15.27 mph 1.59 min.
April 2013 1.93 min. 1.55
16.36 mph 0.82 min.
-33% 7% -48%


Traffic accidents on Ashford Dunwoody Road at or near the I-285 interchange for 11-month period before and after redesign.*

June 2011-April 2012: 61

June 2012-April 2013: 49

*May has been omitted because data for 2013 is not available.

What’s next?

Besides the Pleasant Hill Road and Jimmy Carter Boulevard redesigns at I-85, diverging diamond designs are being considered at these locations: I-75 at Wade Green Road in Cobb, I-285 at Camp Creek Parkway in Fulton, I-20 at Ga. 138 in Rockdale County.

Sources: Dunwoody Police Department, Georgia Department of Transportation, Perimeter CIDs