On I-275 in Tampa, FL, it doesn’t matter if a driver is winding north past the international airport, jutting in and out of a slew of cars lined up like a herd of cattle. Nor does it matter if that same driver is skirting south jamming the breaks, the view of the city bucking with the movement of the car. It’s inevitable –– the driver’s going to hit “Malfunction Junction.”
“We are ready to put more function into that junction,” said John McShaffrey, public information officer of the Interstate Construction Office District 7.
In October 2002, an $80- million construction project started on I-275 between the Hillsborough River and Florabraska Avenue. At the same time, construction began on I-4 from west 19th Street to the Tampa interchange.
The Florida Department of Transportation (FDOT) awarded Granite Construction the contract, which is being shepherded by Wayne Roberts, project manager.
The job site takes up only 2.7 mi. (4.3 km) of the highly-congested residential and commercial area. When completed, 18 existing bridges will be widened and eight new ones will be built to route traffic in a smoother, safer pattern. FDOT also is making I-275 four lanes in each direction.
The most prominent of the structures is a new flyover ramp that will feed southbound I-275 traffic into eastbound I-4 lanes. The curved steel girder bridge has seven spans that range in length from 108 to 206 ft. (33 to 61 m). The bridge’s outside girders — which are 66 in. (168 cm) tall — are suspended from the interior girders, an engineering trick to increase clearance between the flyover and the lanes beneath.
“Malfunction Junction” was originally designed to deal with considerably fewer than the 180,000 vehicles that use it daily, leaving motorists in a quandary on how to safely enter the flow of traffic, regardless of the direction they are driving. Where Interstates 4 and 275 meet in Tampa there are a number of exits leading traffic into downtown. Because of this, travelers merging from I-4 need to quickly cut across three lanes of traffic in order to avoid the cars merging three lanes to the right.
Commuters often risk being sideswiped, rear-ended or left on the wrong side of the road, missing downtown destinations entirely. Others are forced to exit prematurely when “exit only” lanes appear like pop-up ghosts to tease unsuspecting newcomers who want to remain in the traffic flow.
“This is a very congested area with high traffic volume,” noted McShaffrey. “Surprisingly, the traffic flow has not been worse since construction started.”
Construction plans originally included the installation of heavy steel sheet piles to retain the existing soil. Under normal circumstances, a crane would lift the sheets in place and a vibro-hammer would pound them approximately 30 ft. (9.1 m) into the ground while the contractor excavated and prepared to install new walls. These piles were intended to be installed, then cut off and left in place once the new walls were built.
Because of the equipment needed, a majority of the walls would have been installed at night under lane closures. To mitigate this, Granite proposed using a system of “installed-in-place” soil nail walls to replace the steel sheet pile system. The soil nail wall can be placed outside of the traffic lanes, meaning it can be done during the day, increasing production and significantly reducing the potential for noise complaints. This ultimately saved FDOT money.
“Making the decision to use soil nails in this project will be not only economically better, but will save the project from many problems and complaints,” Gary M. Granata, senior project engineer and associate vice president of CEI Construction Engineering and Inspection.
The use of soil nails eliminates a great deal of noise in installation, stopping vibration. The soil nails will be drilled approximately every 5 ft. (1.5 m) horizontally into the existing bank. With the nails in place, the bank will be built and the whole area covered with mechanical stabilizer panels (MSEs), which will be used to form the vertical walls.
Shoulder mounted 8-ft. (2.4 m) noise walls will be built on top of the banks adjacent to densely-populated housing areas. According to FDOT, every effort is being made to minimize disturbance to local residents.
Because of the traffic volume and limited downtown exits, there is limited access to work site. Much of the area outside the right of way is residential, so mobilizing heavy equipment and delivering material –– fill and girders –– is a difficult task.
FDOT is not allowed to close during the day, peak hours or not. With the exception of a few lane shifts and one temporary ramp, traffic has remained in the existing patterns helping to reduce confusion.
Any work that requires a lane closure can only be done between the hours of 10 p.m. and 5:30 a.m. Because of traffic volume, crews operate on a limited nighttime work schedule, which often limits production. To set up, close and reopen a lane requires approximately one hour of labor.
Complicating matters more, lanes that lead to Ybor City, a popular Tampa entertainment district, cannot be closed on Friday and Saturday nights because of the volume of people going to and from the area.
Still, off-interstate detours do interrupt traffic flows and are necessary to give the contractor the time and access needed for certain complex operations, like the girders for the new southbound I-275 to eastbound I-4 ramp, or the sign truss that spans I-275 at Florabraska Avenue.
Despite these limitations, McShaffrey believes the job is progressing exceptionally well. “Granite Construction has been cooperative and professional and is partnering well with FDOT. We are currently within the schedule and on target to complete on time [in 2006].”