Inspecting the World’s Largest Diverging Diamond Interchange

Sarasota County, Florida, has seen a surge of economic and residential development in recent years. Its growth is due, in large part, to a new regional shopping mall and the redeveloped Nathan Benderson Park, which hosted the 2017 World Rowing Championships on its 400-acre man-made lake.

As Sarasota has grown, so too have traffic volumes. Leading up to the international regatta, the Florida Department of Transportation (FDOT) implemented the world’s largest and Florida’s first diverging diamond interchange (DDI) to alleviate congestion and improve safety at the Interstate-75/University Parkway interchange, one of the state’s largest bottlenecks.

FDOT had a deadline to complete the DDI before the rowing competition came to town in September 2017. The department turned to CDM Smith, as a sub-con­sul­tant to Metric Engineering, to provide construc­tion engineering and inspection (CEI) services for the $75 million interchange recon­struc­tion. “FDOT understood the national attention the DDI project brought because of its size,” said CDM Smith associate client service leader Amy Davies. “They wanted a CEI team they trusted to act as an extension of their staff, ensure that construc­tion activities were completed safely and keep the contractor accountable to the schedule.”



According to Christopher Pecor, PE, associate senior CEI project engineer, CDM Smith’s inspectors brought timely experience and strong local rela­tion­ships. “A couple years before, we had provided CEI for Sarasota County’s creation of the North Cattlemen Road connection,” said Pecor, “which is the main access road to Nathan Benderson Park and its 30-acre island that includes a five-story tower at the finish line.” A trusted partner for that $14.5 million roadway project, CDM Smith also facilitated five construc­tion change orders that increased the project’s scope to more than $22 million to accommodate the island’s footprint and infra­struc­ture. 

For the 2017 DDI, CDM Smith’s team oversaw construc­tion of mechan­i­cally stabilized earth walls, asphalt placement, utility pipeline density testing, and the incor­po­ra­tion of signal­iza­tion and intelligent trans­porta­tion systems.  Utilizing their county and local rela­tion­ships, CDM Smith also supported CEI team management and FDOT with local coor­di­na­tion, education and commu­ni­ca­tion. 



CDM Smith also enlisted its certified drone pilots to capture bird’s eye footage of the DDI when it opened to traffic. “To go from one config­u­ra­tion to the opposite is probably the hardest part of one of these jobs,” explained Pecor. “People can under­stand­ably get confused when they haven’t experienced an interchange design like this before.” According to Pecor, CDM Smith offered the drone flight as a value-added service to FDOT, to give the agency another tool to educate its stake­hold­ers and the public moving forward—the I-75/University Parkway project sparked a wave of 35+ new DDI projects in Florida. “Luckily, the changeover went off without a hitch,” he said. “Drivers adapted to it naturally, which is what we wanted.”



With the impending rush of people coming from all corners of the globe to the regatta, FDOT was challenged with a tight deadline. Key to the project’s success was commu­ni­ca­tion between all team members and stake­hold­ers. Under­stand­ing the criticality of the schedule, Pecor and his team were available to respond to issues at a moment’s notice. “For example,” he said, “I got a text at 10 p.m. one night that a storm had downed a tree, which was laying across the southbound access on-ramp to the interstate. I called the contractor and met the construc­tion team on site within 15 minutes to clear the road and re-open it.” 



“To be a truly valuable CEI resource,” added Davies, “you have to be willing to give that kind of extra effort. That’s how our team tries to operate.”



Success­fully delivered and now complete, the DDI helped FDOT meet traffic demands and improved safety for drivers, bicyclists and pedestrians, and, after winning state and regional honors, earned a 2018 National Recognition Award from the American Council of Engineering Companies.