Many a motorist has entered the fog zone, often in the dark of night, and been taken by surprise; some have suffered injury and even death in vehicle pileups. One often-repeated story is that of a state trooper who encountered smoke and fog so thick, he could not see the blue light atop his patrol car as he stood at the hood of the vehicle.
State and federal highway officials decided several years ago it was time to make the roadway safer, but not just for the 22,000 motorists a day who pass through this often-treacherous area. It was time to help other drivers across the nation who fight fog, smoke, dust and blinding snow on the highways. They requested proposals for design of a state-of-the-art visibility detection and warning system.
Engineers at the Georgia Tech Research Institute in Atlanta proposed a solution, and this summer, a $2.4 million, automated fog and smoke warning system is expected to become operational on Interstate 75 near Adel, Ga., just 35 miles north of the Florida state line. Georgia Department of Transportation (GDOT) officials call it a model system that could be implemented wherever visibility problems regularly occur.
"We always had in mind that we were building a model system based on the original requests for proposals from the Federal Highway Administration and the GDOT," says GTRI project manager Gary Gimmestad. "We believe this system will improve safety in this area (near Adel), and we want it to be applied elsewhere."
At the heart of the system's data collection operation is a set of 19 commercially available fog sensors. Each sensor has a transmitter and a receiver. The transmitter is angled away from the receiver, so that in clear conditions, its light beam misses the receiver. But when fog or smoke particles are present in the air, they scatter some of the light into the receiver. The sensor detects this light and sends a reading to the system's on-site computer.
image courtesy Wayne Daley
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GTRI researchers Marlon Moses and John Trostel check the operation of one of the fog sensors in the warning system along I-75 near Adel, Ga.
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The computer, linked to the system's components via a fiber optic network, is located inside a concrete building alongside the interstate in the fog zone. The computer collects data not only from the fog sensors, but also from an adjacent weather station, speed detectors on the highway and television cameras, which GDOT officials can operate remotely to scan the area. Also, the computer contains several telephone modem lines so officials can remotely upload and download data from the site.
A team of GTRI researchers led by engineer Richard Carey designed the overall system layout, as well as its hardware and software. Technician Marlon Moses assisted with the hardware selection and the design of interfaces to the fog sensors, and power control and protection components. The fog sensors are descendants of airport visibility technology.
The system's software analyzes data from the fog sensors, notifies GDOT officials at the Transportation Management Center (TMC) in Atlanta of potential problems and automatically decides what message to post on four changeable message signs on the north- and southbound outskirts of the fog zone. The 36-foot-wide and 9-foot-high signs are attached to metal structures built over the highway.
When the fog warning system detects a decline in visibility to a certain level, it automatically notifies the TMC and also sends a caution to motorists via the changeable message signs. It also turns on streetlights along the roadway. If visibility drops to a second threshold, the system again notifies the TMC and then issues a speed advisory to motorists via the signs. The system recognizes two additional lower levels of visibility and again alerts the TMC and issues advisories to motorists to further decrease their speed.
TMC personnel will have a protocol for notifying local officials, who could put GDOT people on the scene at some point as the visibility gets worse.
"That is when the television cameras will be useful," Gimmestad says, "because they will give local GDOT people a visual impression of conditions at the scene."
image courtesy of Cindy Lane, GDOT
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Contractors install the changeable message signs that will warn drivers of thick fog and poor visibility on a 14-mile stretch of I-75 in south Georgia.
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In very poor conditions, local officials may decide to close the road and detour traffic, if this is warranted.
GDOT project manager Timmy Rowe believes the GTRI warning system will greatly enhance safety in the fog-plagued area. "Safety is the key," he says. "This has been a problem area for years, and we're hoping this system will improve safety."
GTRI researchers hope to conduct a follow-up study on the warning system after it becomes operational. "We want to study the system's maintenance requirements and accuracy," Gimmestad says. "We also want to look at human factors, such as whether drivers are really slowing down when they see warnings on the changeable message signs."
In designing the warning system, GTRI engineers found that various systems, usually simpler ones, have been in use since the early 1980s. The only other similar system in the United States is one on I-75 in Tennessee, but it is not an automated system. So the system near Adel is unique in this nation, though Europe is home to several automated warning systems, Gimmestad says.
The Adel system could be implemented elsewhere at a much lower cost because all of the design work is completed, GTRI project engineer Wayne Daley says. It would only require slight modifications of the software and hardware. The system could even be calibrated to detect dust or snow, rather than fog and smoke.
"The system near Adel is definitely going to attract more attention once it starts operation," Daley says. Indeed the researchers have already gotten inquiries from transportation departments in West Virginia, Alabama and Florida.
For more information, contact Gary Gimmestad, Georgia Tech Research Institute, Atlanta, GA, 30332-0834. (Telephone: 404-894-3419) (E-mail: gary.gimmestad@gtri.gatech.edu);
or Timmy Rowe, Georgia Department of Transportation, 120 East By-Pass NE, Moultrie, Ga., 31768. (Telephone: 912-891-7130) (E-mail: timmy.rowe@dot.state.ga.us)
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Last updated: July 14, 2001
