Georgia’s First DDI Improves Safety and Travel Time

The transformation of the Ashford Dunwoody interchange at

I-285 into Georgia’s first Diverging Diamond Interchange (DDI)

opened in 2012 and has been successful in improving travel

time and reducing crashes. The Ashford Dunwoody Road/I-285

interchange had been the subject of many traffic studies and

design concepts for more than 20 years. Carrying 54,000 trips a

day, it was operating above capacity and causing safety and

operational issues.

To address these problems, the Georgia Department of

Transportation (GDOT) implemented the DDI as an alternative

that eliminated the need to replace the existing bridge,

at a tremendous cost savings over other options that were

considered.

The interchange was previously studied on numerous occasions

and complete reconstruction alternatives were estimated at

costs of up to $172 million. The DDI at the Ashford Dunwoody

Road/I-285 interchange, at a cost of $6.4 million, has improved

traffic flow and safety at a major gateway into the Perimeter

area of Dunwoody, Georgia. Additionally, a comprehensive

public information campaign educated stakeholders and the

driving public about the new interchange design, increasing

confidence in and awareness of the project.

🞂 Fewer potential conflict points between leftturning vehicles and oncoming arterial traffic.

🞂 Pedestrians use signalized crossings with a 

protected pedestrian pathway in the middle 

of the interchange.

🞂 Improves traffic flow without needing more 

lanes. 

🞂 Better signal network synchronization.

For a Retrofit

🞂 Existing bridge can usually be used.

🞂 Additional right-of-way is rarely needed.

🞂 Construction time is reduced.

For a New Interchange

🞂 Typically fewer lanes and less bridge structure 

than other interchange forms.

Supporting Data

🞂 In the year following completion of the 

Ashford Dunwoody DDI, there were about 20

percent fewer crashes near the interchange 

than were reported in the same time period 

before the DDI project began.

🞂 Traffic observations before and after the 

Ashford Dunwoody DDI show fewer stops and 

improved travel times through the interchange area.

🞂 By using the DDI design, the project retained 

the existing Ashford Dunwoody Road Bridge, 

saving significant cost without precluding any 

future interchange improvements that may 

arise from improvements to I-285.

Intersection and 

Interchange Geometrics

BENEFITS OF DDI

Safety Operations Cost

PROJECT CASE STUDY
Every Day Counts (EDC), a State-based initiative of FHWA’s Center for Accelerating 

Innovation, works with State, local and private sector partners to encourage the adoption of 

proven technologies and innovations aimed at shortening and enhancing project delivery

www.fhwa.dot.gov/everydaycounts

For additional 

information, 

please contact:

KEYS TO SUCCESS

The success of the Ashford Dunwoody DDI was 

predicated by a comprehensive public information 

campaign spearheaded by the Perimeter Community 

Improvement Districts (PCID). Focused on combating 

concerns about the proposed change in traffic 

patterns, PCID used creative communications 

and outreach methods—such as ongoing media 

campaigns and public and private stakeholder 

participation in town hall meetings—to promote 

acceptance of the innovative design.

The PCID’s campaign included the eye-catching 

graphic and slogan, “Can You DDI? Arrive, Crossover, 

Drive.” Because of the efforts of the PCID to 

engage all who might be affected by the project’s 

implementation, the Ashford Dunwoody DDI was 

not only successfully implemented, but the GDOT 

projects that it could become a model for congested 

interchanges throughout the State.

ADDITIONAL RESOURCES

🞂 Ashford Dunwoody/I-285 DDI Visualization Video, 

http://www.youtube.com/watch?v=gY8xU-UAQWs

🞂 PCID “Can You DDI?” website, http://www.

perimetercid.org/canyouddi/

🞂 FHWA Public Roads Magazine, “Design at the 

Crossroads,” http://www.fhwa.dot.gov/publications/

publicroads/13julaug/01.cfm

🞂 FHWA TechBrief, “Drivers’ Evaluation of the Diverging 

Diamond Interchange,” http://www.fhwa.dot.gov/

publications/research/safety/07048/index.cfm

Mark A. Doctor, P.E. 

Intersection and Interchange Geometrics Lead 

Safety & Design Engineer 

FHWA Office of Technical Services 

mark.doctor@dot.gov

Susan Long

Communications Consultant

Perimeter Community Improvement Districts (PCID)

Atlanta, GA 

slong@perimetercid.org

Keys to Success

🞂 Media campaigns and transparency 

to inform and educate the public and 

stakeholders on the new initiative.

🞂 Active and ongoing participation in town 

halls and meetings. 

🞂 Active and ongoing stakeholder 

engagement, buy-in, and promotion.

🞂 The presence of partnership champions 

including state officials and key local and 

large businesses.