Lighting planned for the aesthetic viaduct would make the bridge a landmark in the city’s evening skyline. A continuous linear light-emitting diode light source concealed in a valance along one vertical edge of each tower surface would wash those surfaces with color-changing light. T.Y. Lin International
The Florida Department of Transportation (FDOT) has big plans to rebuild an outdated section of I-395 to bring the expressway up to current safety standards and improve its aesthetics, including the addition of an impressive new signature span.
February 26, 2013—The planned reconstruction of Florida’s I-395 corridor will transform the driving experience for motorists traveling between the city of Miami and its South Beach neighborhood. The Florida Department of Transportation (FDOT) plans to replace the highway from the I-95/ Midtown Interchange to the MacArthur Causeway with an elevated, six-lane, 1.4 mi, state-of-the-art expressway that includes a dramatic new bridge.
The reconstruction will replace an almost 50-year-old section of I-395 that is fraught with safety and operational deficiencies. Built in the 1970s, the existing highway’s deficiencies include low clearances, substandard weaving distances, and inadequate traffic separation. Traffic volume reaches 93,000 vehicles a day—far more than the highway was designed for—and is projected to reach 120,000 by 2020 and 160,000 by 2040, according to the FDOT.
The Federal Highway Administration approved the corridor reconstruction project in 2010. Preliminary design began in 2011; the FDOT engaged the San Francisco-based bridge and highway design firm T.Y. Lin International.
“Context-sensitive design, in which we address not only the engineering requirements but also work with the community to make sure we address their concerns, has been essential on this project,” says Vilma Croft, P.E., the FDOT’s project manager. The project offers an opportunity to address aesthetic and social issues related to the existing highway. “The proposed structure is higher than the existing, allowing for the reconnection of NW 2nd Avenue, [which] was closed with the original construction,” she says. The new design will give the city “the ability to use the space underneath,” Croft adds.
The segmental box continues the highway’s sleek design along
the length of the 600 ft span. With the simplest engineering,
construction, and traffic maintenance requirements, it is the most
economical of the proposed designs. T.Y. Lin International
When the original I-395 was built through the city’s historic Overtown residential district, the highway was elevated just 14 ft above grade and was designed with spans as short as 100 ft. As a result, the neighborhood is visually divided by some 800 concrete piers along the length of the expressway. “This has created not only a visual barrier but also safety concerns due to the low clearance,” Croft says.
The new highway addresses these issues with higher elevations and constant-depth box girders along the entire I-395 corridor; typical span lengths will be 225 ft, says Joe Gomez, P.E., M.ASCE, a vice president of T.Y. Lin International and the firm’s I-395 project manager. “Using a segmental design, we can design a more elegant structure that requires fewer columns,” he notes. “Depending on the final design, there will be between 100 and 150 total columns.”
The project’s most talked-about element is a 600 ft long bridge that crosses Biscayne Boulevard, toward the eastern terminus of I-395. The FDOT has committed to providing a signature design for the structure. From the 15 design concepts that T.Y. Lin International presented, the FDOT has narrowed the selection to four. Although construction is still eight years away, the proposals have already attracted a deluge of public and media attention because of their spectacular, high-tech designs.
The wishbone arch functions as a modified arch, the arch ribs
taking a very slender form. Each roadway is supported
independently, which allows for a phased construction sequence
that minimizes roadway closures. T.Y. Lin International
The design called “segmental box” is the least expensive of the four at an estimated construction cost of $559 million. “This is a very sleek design that uses a series of hollow, trapezoidal concrete boxes, a continuation of the structure of the rest of the highway,” Gomez explains. The design is economical to build and maintain and still offers a significant upgrade over the existing highway, he adds.
At $604 million, the “aesthetic viaduct” concept resembles a cable-stay solution, but the cables do not provide the structural support. Cables are attached to decorative, inverted Y-shaped concrete towers, and the span itself carries the loads. The structural engineers have noted that without loads, the cables will eventually sag, and have therefore suggested altering the design so that vehicle loads are transferred to the cables.
Somewhat more costly at $673 million, the “wishbone arch” is a site-specific design based on an arch bridge with load-bearing struts. Two 245 ft high, asymmetrical steel arches rise from foundations at ground level on either side of the roadways, cross one another above the roadways, and connect to the lanes along the centerline. Each arch spans 680 ft. The design takes advantage of the curves of the roadway by twisting the planes of the struts, which connect to the segmental boxes of the deck.
With an estimated cost of $740 million, the “infinity arch” is the most expensive—and the most dramatic—of the four designs. Designed by London-based Wilkinson Eyre Architects as a subcontractor to T.Y. Lin International, it features two asymmetric steel arches that originate from the same point at ground level, cross over the highway in different planes, and land together on the highway’s other side. A true cable-stayed design, this structure has load-bearing cables suspended from each arch that connect to the opposite edges of the deck. “This is the most complex design because of the load-absorbing requirements at the foundations,” Gomez notes.
The infinity arch offers a distinctive profile that would create an
iconic entryway to the city of Miami from South Beach. The most
complex of the four designs in engineering and construction, it
would require additional phases for traffic maintenance during
construction. Wilkinson Eyre Architects
Final design selection, Croft says, will balance cost, engineering, architecture, constructability, and community expectations. “In terms of aesthetics, the infinity arch is the favorite, but the segmental bridge is more favorable to the budget,” she adds. The FDOT anticipates completing preliminary plans this summer and right-of-way acquisitions by summer 2015.
At this stage, the project is largely unfunded, according to the FDOT. The agency will seek to develop partnerships that will allow the project to be financially feasible. Additional subcontractors to T. Y. Lin International on the project include Miami-based BCC Engineering (project geometry and signing), Doral, Florida-based A & P Consulting Engineers (utilities, lighting, and drainage), Doral-based CH Perez & Associates Consulting Engineers (surveying, right-of-way mapping, and traffic design), Hialeah, Florida-based GEOSOL, Inc. (geotechnical engineering), Miami-based Cunningham Group (public involvement), and Bloomfield, New Jersey-based Illumination Arts (specialty lighting).