New Dampener Makes Traffic Light Poles Safer, Longer-Lasting

May 27, 1998

GAINESVILLE — A mailbox-sized dampener designed by University of Florida engineers greatly reduces wind-driven vibration in traffic-signal poles, increasing their life span and stability.

The Florida Department of Transportation hired UF civil engineers to design the dampener after two signal poles collapsed in Florida and officials received complaints from motorists about the cantilevered poles bouncing on windy days, DOT officials said.

“I don’t know the exact number, but we’ve had numerous complaints from motorists and numerous locations where we’ve had a vibration problem,” said Andre Pavlov, a structural design engineer for the DOT in Tallahassee. “It’s a perception problem, but if you don’t remedy these things they have a potential to fail.”

Shaped like an “L” laid on its side, the traffic light “mast arms” range in length from about 20 to 70 feet and may support as many as five sets of traffic signals.

They are becoming more common in Florida after proving far more reliable than traditional cable-suspended lights during Hurricane Andrew in 1992. State officials said only one was damaged, while more than 2,700 cable-suspended signals broke off and fell, said Ron Cook, a civil engineering professor and co-investigator on the UF project with civil engineering Professor Dave Bloomquist. The DOT now requires the structures at new intersections or intersections where traffic lights are replaced within 10 miles of the coast.

Still, the signal poles are not foolproof. Cook said they have collapsed in Michigan, Nebraska and Florida. One failed in Fort Walton Beach in 1995 during Hurricane Opal and another, unfinished pole collapsed in St. Augustine, Pavlov said.

While no one was injured in the Florida collapses, there is a potential for injury, Pavlov said. A 42-foot mast arm weighs more than 1 1/2 tons, he said.

After testing several possibilities on a 37-foot pole mounted inside a UF laboratory, civil engineering master’s student Mike Kalajian solved the vibration problem with a dampener modeled after dampener used to stabilize vertical light poles, he said.

The dampener is a 26-inch-long, 4-inch-diameter steel cylinder containing a 15-pound weight suspended on a spring. Mounted on the pole’s tip, the weight bangs against the bottom of the steel cylinder when it starts to vibrate, dampening the vibrations, Kalajian said.

Without the dampener, the pole has the potential for as much as 2 feet of movement, he said. The dampener significantly reduces the movement and completely stops it within 10 to 15 seconds from when the pole is first disturbed.

“We’ve taken it out to the field here on 34th Street and put it on the short mast arms and long ones, and it works,” Kalajian said.

UF researchers plan to test the dampener this fall on signal poles along the east coast. If it continues to prove successful, the DOT may install similar dampener on all poles where vibration is a problem, Pavlov said. With the dampener likely to cost less than $200 a piece — far less than the $10,000 to $20,000 cost of the signal poles themselves — the DOT may even decide to install them on all the poles, he said.