 |
||||||||
 |
||||||||
|
||||||||
Back
|
A slingshot stop
By BILL VARIAN, Times Staff Writer TAMPA -- Traffic engineers fully expect drivers to be confused by a planned Hillsborough County highway that changes directions with every rush hour. So they latched onto an innovation to thwart any motorist who might be inclined to enter the highway against the tide. A net. Really. "It's kind of like a slingshot," said PerryDawn Brown, director of communications and business development for the Tampa-Hillsborough County Expressway Authority. Mercifully, the Dragnet, as it is called, will simply snare errant vehicles rather than catapult them backward. The Dragnet is featured in a new Expressway Authority video promoting construction of the 9-mile Reversible-Lanes Bridge, which is scheduled to begin this summer. The elevated highway, which will open in 2004, will be built in the median of the Lee Roy Selmon Crosstown Expressway and will link Brandon with Tampa's Channelside district at a cost of $350-million. It features three lanes that will carry traffic in one direction, changing with each rush hour. During the mornings, traffic will flow west from Brandon. In the afternoons, it will flow east. The road will be closed the rest of the time. Cars that turn onto the entry ramp at the wrong time will be greeted by two railroad-styled crossing arms blocking their path, and a sign warning them not to enter. "But we know that with similar facilities there have been people who have run through the gates," said Jim Phillips, vice president of Tampa-based E.C. Driver & Associates, an engineering consultant on the project. With three lanes of oncoming traffic, that would be bad. Enter the Dragnet, which would be lowered from the overhead sign and span the width of the entry ramp.
The Dragnet is manufactured by the Entwistle Co. of Hudson, Mass., west of Boston. It's an adaptation of equipment used on aircraft carriers and at airports to catch planes that overshoot the runway. With advances in airplane braking systems hurting their market, Entwistle began looking for new applications for their equipment. They found interest among road builders. Around Florida, Dragnets sometimes have been used to replace the precast concrete barriers near roadway construction projects to lessen damage to the cars of careless drivers. They also have been installed before drawbridges, such as the Main Street Bridge in Jacksonville and the nearby Astor Bridge, where State Road 40 crosses the St. Johns River. People in more hilly regions of the country are accustomed to seeing runaway truck ramps on downward sloping highways. In some cases, a series of Dragnets have replaced the gravel mounds at the end of the ramps, again in an attempt to curb damage to trucks. A month after installing a Dragnet system at a truck ramp in Williamstown, Mass., last summer, a semitrailer truck loaded with Kahlua Liqueur put it to the test. "And none of the booze bottles were broken, so it was a major success," said John Rhatigan, a vice president with Entwistle. Entwistle has recently produced Dragnets for use on reversible high-occupancy vehicle lanes in Dallas and Chicago. The company produces Dragnets of varying strength, some geared more toward cars, and others capable of stopping a 100,000-pound truck, Entwistle said. Appearing somewhat like tennis nets, Dragnets typically feature two metal cables with heavy-duty meshing in between. When struck by a vehicle, a pair of spools on either side of the road unfurl more of the cable, gradually slowing the vehicle and absorbing the energy produced by its weight, mass and speed. Rhatigan said he has personally tested the equipment three times, earning him a company nickname of crash test dummy. "It's like someone sticking out a giant hand and grabbing you and slowing you down," he said. "It's less than slamming your brakes on." Depending on the traveling speed of the vehicle and the model of the Dragnet, the force can be enough to cause air bags to deploy. Generally, though, that doesn't happen, Rhatigan said. It also can cause minor damage to a car, such as dents to the hood and scratches to the paint. "But if you've gone through a couple of barriers already, you probably should get the wakeup call," said Phillips, the engineering consultant. Sound like fun? Consider this: Part of the mechanism that makes the Dragnet work must be replaced after each use. The cost: about $10,000. The Expressway Authority intends to pass that cost along in fines to anyone who deploys it, along with the cost of replacing broken barriers. That's a practical step to recoup costs. Authority officials hope it also will discourage the curious. "Thrill seekers hopefully will be deterred by the cost," said Brown, the authority's communications director. "If they have that kind of income, hopefully they'll do something more lofty, like climb Mount Everest."
 © 2006 • All Rights Reserved • St. Petersburg Times
490 First Avenue South • St. Petersburg, FL 33701 • 727-893-8111 
|
Headlines From the Times local news desks |
