6 minute read
A Sparkling Example: Improving I-95 With District 4’s First Diverging Diamond Interchange
By Richard Reitz, WSP
ACEC Florida: Outstanding Special Roadway Project AwardDBIA Florida Region: Design-Build AwardFlorida Transportation Builders’ Association (FTBA): Florida’s Best in Construction Interstate and Florida’s Best in Construction Design-Build
Not long ago, traveling along Interstate 95 (I-95) in Palm Beach County — one of the most heavily traveled sections of urban interstate in the nation — could be a rough experience for motorists.
Today, thanks to the implementation of express lanes to a perennially congested 5.8-mile corridor of I-95 along with innovative interchange design at State Route 808/Glades Road, the Florida Department of Transportation (FDOT) has found its diverging “diamond” in the rough.
Congestion relief and future growth potential were crucial considerations when the decision was made to design the first diverging diamond interchange (DDI) in FDOT District 4 as part of the $148 million I-95 Express Lanes Phase 3B-2 design-build (DB) regional road network improvement project.
“The DB team, led by Prince Contracting, LLC, had innovative ideas to improve the Glades Road interchange that was working at capacity and projected to be over capacity with failing levels of service in design year 2040,” said Yamila Hernandez, senior vice president project manager for WSP, the engineering, environment and professional services firm that designed the highway project. “The DDI was presented and approved as an alternative technical concept (ATC) to the FDOT concept design during the procurement of the project. This innovative transformation improved traffic operations, reduced congestion and enhanced safety.”
The DDI concept stood out by delivering $5 million cost and schedule savings through the elimination of right-of-way acquisition, utility relocations, a flyover bridge and a substantial reduction in retaining walls.
Compared to a conventional diamond interchange, the DDI reduces vehicle-to-vehicle conflict points by 50% and helps lessen severe crash incidents. DDIs eliminate left-hand turns into oncoming traffic by forcing traffic to flow from the right side of the road to the left side of the road, then back again.
“Think, veer left to turn left,” Hernandez said.
Consistent, Dependable Traffic Movement
A little more than a decade ago, with more than 200 miles of major highways and 50 major intersections in Palm Beach County experiencing conditions close to or over capacity following rapid population growth, FDOT began to consider its options to keep traffic moving and motorists safe.
In 2013, traffic in this corridor was exceeding 200,000 vehicles per day, and projections anticipated an increase to 300,000 vehicles per day by 2040. FDOT completed a project development and environment study to improve capacity along Interstate I-95, which led to this extensive roadway and interchange project.
The result was the I-95 Express Lanes Phase 3B-2 design-build project along I-95 from just south of Glades Road to south of Linton Boulevard in Palm Beach County. It included improvements at the I-95 interchange with State Route 808/Glades Road and along State Route 808/Glades Road from Renaissance Way to West University Drive.
Within this 5.8-mile section of I-95, existing HOV lanes were converted to managed lanes and widened to produce two tolled express lanes in each direction while maintaining the existing number of general use and auxiliary lanes.
Implementation of the DDI provided enhanced safety at the Glades Road interchange by:
Reducing the number of conflict points
Improving intersection sight distance
Implementing wrong-way driving countermeasures at the off-ramps
Providing shorter pedestrian crossings, a shared use path along the interchange and buffered bicycle lanes along Glades Road
Installing enhanced overhead signage and lane guidance pavement markings in advanced or decision points
Eliminating an additional signalized intersection at Airport Road
“These capacity improvements have provided motorists and bus transit users with a viable option for consistent, dependable and safe north/south traffic throughout the tri-county area in southeast Florida,” Hernandez said.
Significant Safety Improvements
A primary benefit of the project was the improved safety that came with the new interchange configuration. It is projected that the DDI will result in a 33% crash reduction at the SR-808/ Glades Road and I-95 interchange, and a projected 9% crash reduction along SR-808/Glades Road.
The intersection design made it safer for other road users as well.
“To enhance pedestrian and bicyclist safety and accessibility within the DDI, we strategically placed a separate shared use path pedestrian bridge in the median along Glades Road between the crossover intersections,” Hernandez said. “This innovative placement of the pedestrian bridge eliminated the need to acquire additional right of way or reduce lane widths, ensuring efficient, safe traffic flow for all users.”
The pedestrian bridge along Glades Road over I-95 and the replacement of the Clint Moore Road bridge over I-95 also utilized Florida I-beams — pre-stressed beams developed by FDOT to improve the design of bridge beams — to maintain a consistent aesthetic throughout the corridor.
Community Outreach
Convincing the public that an unconventional concept like DDI would address some of their biggest concerns took some effort.
Throughout design and construction, an educational campaign showcased how DDI’s are safer, provide greater traffic throughout and improve the level of service for the interchange and the arterial.
Outreach strategies included a construction-specific website as the virtual home front for the project, a 32-hour mobile billboard drive through campaign, a media blitz with educational videos, door-to-door contact, media days, social media blasts and attendance at other public events.
Throughout construction, a monthly “Coffee with the Contractor” meeting was held to discuss construction concerns and issues. Here the public could speak with Prince Contracting, as well as the project’s public information officer and a construction engineering and inspection representative.
“We explained how the DDI, in terms of traffic levels, significantly improved traffic along Glades Road and the interchange ramps that eliminated spill over onto I-95,” Hernandez said. “Overall, the DDI was economically, aesthetically and operationally superior, creating a landmark for the city, its residents and politicians.”
Started in 2019 and despite the challenges of maintaining a construction schedule through the Covid-19 pandemic, the project was completed 21 days ahead of contract time and within budget.
“Through unwavering collaboration among all team members, the DDI serves as a successful model for how active participation can drive the creation, development and implementation of innovative infrastructure,” Hernandez said.
