NO. 7 ROAD: The big six

Oct. 4, 2018

Florida DOT finishes world’s largest DDI

Since 2009, dozens of diverging diamond interchanges (DDIs) have been built across the U.S. None, however, have been delivered in the state of Florida until this year, when the I-75 Interchange Project at University Parkway in Sarasota involved the construction of the state’s first DDI along with the widening of over 3.5 miles of the interstate. The I-75/University Parkway DDI has five lanes in each direction approaching the DDI with six lanes in each direction under the I-75 bridges. The number of lanes involved makes this the largest DDI in the world, according to Florida Department of Transportation (FDOT) officials.

University Parkway is a major east-west corridor along the Manatee and Sarasota County lines connecting major developments. The interchange is one of Florida’s busiest, with 130,000 ADT on I-75, and between 33,500 and 47,500 ADT on either side of University Parkway. It has become known to be one of the largest bottlenecks in Southwest Florida, as traffic volumes along the interchange have increased to the point of daily hours-long backups in recent years. The results of the DDI configuration cut traffic delays in half, eliminate 12 conflict points and improve sight distance for drivers. The improvements are expected to reduce accidents rates by 30%. The design also provides extra safety for pedestrians, with bike lanes, signal-protected crosswalks and a 14-ft-wide walkway.

One of the major challenges on this signature project was the commitment by FDOT to significantly complete the work before the 2017 World Rowing Championships which were to be held in the area in September of that year. “The commitment for early completion effectively required use of accelerated construction techniques, application of significant manpower and resources, as well as proactive and innovative approaches for timely issue identification and resolution,” Marlena Gore, FDOT District One project manager, told Roads & Bridges. The project was completed under budget with the final amount paid to the contractor being more than $1 million below the original contract bid.

The I-75/University Parkway project was the first and only project known to have a DDI traffic pattern implemented and opened over a one-night operation. FDOT and its partners were able to accomplish this with advanced planning and preparation. “One of the significant challenges was the installation of the new traffic signals,” Gore said. “Temporary lanes and temporary signalization had to be installed to the outside of the existing lanes to accommodate traffic during the multiple phases of the widening.” The critical work components to accomplish an overnight DDI implementation included removing temporary signals; repairing the asphalt pavement; switching to permanent signals; removing temporary striping; and restriping six lanes of traffic in each direction.

Project: I-75/University Parkway DDI

Location: Sarasota, Fla.

Owner: Florida Department of Transporation

Designer: HDR Engineering Inc.

Contractor: Prince Contracting LLC

Cost: $78,432,970.14

Length: 3.5 miles

Completion Date: May 17, 2018

About The Author: Bruns is associate editor of Roads & Bridges.

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