ddi logoPleasant Hill Road Bridge DDI Rendering

The Pleasant Hill Road bridge over I-85 opened June 9, 2013 as a new Diverging Diamond Interchange (DDI). The bridge at Pleasant Hill Road and I-85 is Gwinnett County’s first DDI and the second DDI in Georgia.

The "before" and "after" results (which included travel runs from Club Drive to Satellite Boulevard along Pleasant Hill Road) show a 51% decrease in the average number of stops and a 43% decrease in total delay along that portion of Pleasant Hill Road.

DDI at Day

Over the past several years, the Gwinnett Place CID funded feasibility studies and conceptual layout plans for the much-needed improvement and ultimate reconstruction of the Pleasant Hill Road at I-85 interchange.  The Gwinnett Place CID, Gwinnett County DOT, Georgia DOT and the State Road and Tollway Authority began construction in 2012 to redesign the congested Pleasant Hill Road at I-85 interchange into Gwinnett's first Diverging Diamond Interchange.  

This innovative transportation design shifts vehicles to the opposite side of the road to improve traffic flow. By reducing possible points of conflict, the DDI design allows for a significant improvement in safety, since no left turns must clear opposing traffic. Around the nation, DDIs are a proven, cutting edge, low-cost project design that provides immediate traffic relief.

The DDI at I-85 and Pleasant Hill Road project included the following improvements:

New traffic signals align with the new lane configurations, and improvements have been be made to the signal timing to help traffic flow within the corridor.

The existing bridge deck was maintained, but the existing outside barrier wall and sidewalk were removed. The new barrier wall has been constructed on the outside of the existing deck.

This project included the construction of sidewalks and streetscapes along the Pleasant Hill Road corridor from Breckinridge Boulevard/Shackelford Road to Venture Drive/Venture Parkway. When the sidewalk reaches the ramp intersections, the pedestrians are now directed to cross the right-turn lanes to walk across the bridge in the median. An 8-foot sidewalk has been constructed along the median of the bridge, flanked by barrier walls.

DDI Aerial

Benefits of the DDI at Pleasant Hill Road and I-85:

  • Safety Advantages:
    • One of the most compelling benefits of the DDI design is that it increases safety by reducing the number of potential conflict points through eliminating left turns crossing opposing traffic.  This design can equate to as much as a 50% reduction in crashes.
      • A DDI has only14 conflict points and two crossing points compared to a conventional diamond interchange which has 26 conflict points.
      • The DDI has traffic calming features that reduce speeds while maintaining capacity.  This results in fewer and less severe crashes than a conventional intersection.
      • Dangerous collisions like the T-hone accidents will be minimized.
      • Conflict points spread throughout interchange.
    • Better sight distance at turns.
    • Virtually no driver confusion has been documented at the DDIs already constructed in the US.
    • Wrong way entry ramps extremely difficult.
    • Pedestrian safety and mobility will also be improved at the interchange through the construction of sidewalks, signalized crossings and lighting.
  • Operational Advantages:
    • Moves traffic more quickly because the number of places where traffic must stop is reduced.
    • Continuous left lane movements onto the Interstate.
    • New design able to accommodate an extra thru lane of traffic on both sides of the bridge.
    • Overall traffic congestion delay will be reduced at the interchange.
  • Cost Advantages:
    • Existing bridge can be used.
    • Limited need for additional right-of-way.
    • Reduced impacts to the environment.
    • Maintenance of traffic is simplified during construction.
    • Less infrastructure to construct, maintain and replace.  This leads to reduced construction and maintenance costs, including the time of construction and delays created while maintaining traffic during construction.
    • Shorter construction schedule.

Click here to view a Gwinnett County video detailing the advantages of the DDI.

Visit Gwinnett County DOT's Gwinnett DDI Web site for full details on the DDI


 (DDI graphic courtesy of Nicole Puckett/Gwinnett Daily Post.)


CID-funded studies, presentations and materials related to the Pleasant Hill Road at I-85 DDI bridge project:


DDI Image




From a long-term perspective, the CID one day will seek to completely replace the existing bridge infrastructure.  The proposed single point urban interchange (SPUI) would greatly enhance mobility and safety in this heavily congested corridor. 

The SPUI design was selected as the preferred alternative design concept for the intersection's ultimate reconstruction because:

  • Design developed in the 1970s and a proven record for successful movement of traffic in urban areas. Today, over 300 SPUIs in US.
  • Beneficial in urban areas because it can be constructed in limited rights-of-way…uses less land. Minimal right-of-way needed compared to right-of-way required for other types of interchange designs.
  • Reduces traffic signals.
  • Increases capacity and reduces commute times... moves more cars faster.

Click the links below to view the feasibility study reports and conceptual plans:


Appendix A: Conceptual Plan A1-1
Appendix A: Conceptual Plan A1-2
Appendix A: Conceptual Plan A1-3
Appendix A: Conceptual Plan A1-4
Appendix A: Conceptual Plan A1-5
Appendix B: Cost Estimate

During 2008 and 2009, in concert with the Gwinnett Department of Transportation, the Georgia Department of Transportation and the Federal Highway Administration (FHWA), the CID funded the interstate modification report (IMR) for the Pleasant Hill Road Bridge. The IMR is a crucial step toward gaining approval for the reconstruction project.  The project has recently received approval from the FHWA on the IMR, which is the first step in replacement of a bridge over an Interstate.  FHWA concluded that based on the initial analysis of the IMR, a full IMR was not required.  Click the links below to view the IMR technical reports and studies: