Always passable

The Alabama Department of Transportation (ALDOT) has installed a de-icing/anti-icing system on the O’Neal Bridge, which spans the Tennessee River and connects Florence, Ala., and Sheffield, Ala. During the winter months, the system monitors the weather and automatically dispenses a de-icing/anti-icing agent when conditions warrant.

ALDOT purchased the system after the mayors of Florence and Sheffield lobbied for its use on the bridge. In 1997, a severe ice storm paralyzed the cities for two days and made the four-lane, 2,000-foot-long bridge impassable. National Guard units were called in to transport residents across the bridge for needed medical care. Until last summer, the bridge was the only one that connected Florence and Sheffield, which have populations of approximately 36,000 and 10,000 residents, respectively.

William Jordan, mayor of Florence, says the storm emphasized the importance of keeping the bridge, which has an average daily volume of 42,000 vehicles a day, open. “There’s lots of traffic flow between the two cities,” he says.

ALDOT, which maintains the bridge, was receptive to the lobbying efforts of Florence and Sheffield. Through Jim Chandler & Associates, a Homewood, Ala.-based distributor, the state purchased a FreezeFree de-icing/anti-icing system manufactured by Chicago-based Quixote Transportation Safety. It also bought two electric overhead informational roadway signs that were made by Spokane, Wash.-based American Electronic Signs. In all, the state paid about $500,000 for the system and the signs. In spring 2002, Shoals Electric, a general contractor based in Muscle Shoals, Ala., installed both the system and the signs.

The system includes sensors located on the bridge deck and a weather-monitoring device that sits atop a 20-foot pole near the bridge. During the winter months, the device constantly measures a number of conditions, such as air temperature, relative humidity, wind speed and direction, precipitation and visibility. Meanwhile, the sensors measure deck temperature, precipitation on the bridge and the amount of de-icing/anti-icing agent on the bridge. If the conditions indicate the threat of frozen precipitation on the bridge, calcium magnesium acetate (CMA), which is contained in a 700-gallon tank in a pump house near the bridge, is dispensed in liquid form through a series of nozzles onto the roadway to prevent icing.

In all, 114 nozzles are located on and near the bridge. The nozzles also can be manually activated at the pump house or by a telephone code. It takes about 100 gallons of CMA and approximately 20 minutes to spray the entire bridge. The system kept the bridge clear last winter when several snow-and-ice storms hit the area.

The two electric signs are located near each end of the bridge to notify drivers when spraying is taking place. ALDOT also uses the signs, which are about 7 feet tall and 12.5 feet wide, year-round to inform drivers of traffic-flow problems, roadwork and emergencies.