Traffic Analysis Software Helps Reduce Congestion

Maneuvering from Point A to Point B can be risky business if roadway congestion has you suddenly hitting the brakes. Motorists navigating Cascade Road at the I-285 interchange in Fulton County, Georgia, have been dealing with crashes, delays, and other traffic inefficiencies there for years. Congestion along the Cascade Road corridor – a principal arterial just west of downtown Atlanta and northwest of the airport – is only expected to worsen as traffic volumes grow.

Fulton County addressed the issue by launching an investigation into ways to alleviate the congestion and safety concerns impacting the corridor. State-of-the-art traffic analysis software was used to develop three viable alternatives for this highly constrained interchange:

• Conventional diamond interchange with traffic signals
• Conventional diamond interchange with roundabouts
• Diverging diamond interchange with traffic signals

Synchro, a type of traffic analysis software, allowed analysis of each of the signalized intersections as a network to assess how they currently work together and how operations could be improved through lane additions, timing plan adjustments, signal setup enhancements, and other measures. SIDRA provided analysis of the proposed roundabouts at each intersection in a similar manner. Then, once the recommended alternatives were solidified, VISSIM software was used to prepare microsimulation models to show the public a visual representation of how each alternative (shown in the links above) could potentially operate.

VISSIM is invaluable in illustrating concepts for the public. In this case the simulations allowed people to see the pros and cons of each option, how each of the intersections would operate, and how that compared to the layouts prepared by the design team. Additionally, the VISSIM microsimulation model revealed a potential operational issue that would not have been readily found through other modeling efforts involving a signalized intersection. This value-added discovery allowed the project team to document this issue for further examination and consideration.

After several public meetings and much discussion, the County chose the diverging diamond interchange. This is the least expensive alternative but also has the benefits of a shorter construction duration, no relocation of businesses along the corridor, and no changes to the existing I-285 bridges. With a recommended solution in hand, the County now can pursue project funding.

This link has more about Fulton County’s plans for the interchange, the three alternatives proposed to the County, relevant traffic count documents, and more. Ayres Associates’ preparation of a report to summarize all of the traffic analysis details, conceptual drawings to show the impacts of each alternative, and simulations to help the public visualize the project helped the County work with residents and elected officials to reach a consensus on a design alternative to move forward.

Ayres’ Kevin Kuhlow, PE, continued the conversation at the 2016 Institute of Transportation Engineers (ITE) Wisconsin Section’s Traffic Engineering Workshop & Transportation Planning Forum, held April 20 in Pewaukee. Their 30-minute presentation on the I-285 and Cascade Road Interchange Improvement Study provided a case study of innovative interchange alternatives.

For more about these and other traffic- and transportation-related services, contact Kevin Kuhlow, PE.