• Frost warning

  Iowa State student work with Iowa DOT to deliver accurate bridge frost warning

• When you are snug in your bed this winter, think about Tina Greenfield, a graduate student in geological and atmospheric sciences.
  
  Because when most of us are either sound asleep or are just thinking about waking up, Greenfield is already working on her research.
  
  To be fair, Greenfield doesn’t go out every morning before 5 a.m. (she rotates with two other meteorology students, Brian Tentinger and Jose Alamo), but there are times when Greenfield wishes she wasn’t driving the back roads of Story County in search of bridge frost.
  
  "There are sometimes I wish I could get out of it," Greenfield said. "It's at an obscenely early time in the morning.

  "Typically it's extremely cold, you have to scrape your car. It's real tempting just to stay inside."
  
  Instead, virtually every morning, either Greenfield, Tentinger or Alamo will observe whether or not frost has developed on three Story County bridges, all over Highway 30 (State Avenue bridge, South Dakota Avenue bridge and the County Line bridge).
  
  The three bridges were selected because of their close proximity to each other (they are separated by one mile each). Each day that frost can develop Greenfield, Tentinger or Alamo will drive over the bridge and then park the car and get out and use an infrared thermometer to take the bridge pavement’s temperature quickly.
  
  A complete rotation of the three bridges can take up to half an hour. However, if frost is observed, either Greenfield, Tentinger or Alamo can be on site until 9 or 10 a.m.
  
  Frost develops when two criteria occur - the bridge temperature is below freezing and the dew point temperature is above the bridge temperature.
  
  "This is a very sensitive reading," Greenfield says. "If you are off by just a degree or two, it can mean nothing will happen or you could get a large amount of frost."
  
  Because of the criteria necessary to develop frost, the trio of bridge inspectors doesn't go out every day. This is the second year of Greenfield's research (she plans three years of observable data), which is funded by a two-year grant from the Iowa Department of Transportation. Last year, the group went out 60 times and observed frost on 14 different occasions.
  
  Observations are not made when slick conditions already exist (snow or ice) or if the temperature is too high.
  
  The Iowa DOT was interested in Greenfield's project because of potentially hazardous conditions presented to a motorist coming upon a frosty bridge at a high rate of speed.
  
  "The DOT and others are very interested in helping us develop procedures by which we can accurately predict roadway driving conditions in Iowa," said Gene Takle, professor of geological and atmospheric sciences.
  
  "From these observations, we hopefully can develop computer models that will tell us when frost will occur and how much will accumulate. If we are able to develop a model that can predict 18 hours in advance whether frost will occur, then the DOT can have the trucks ready to go."
  
  "Secondary to safety, the DOT is hoping that better prediction will make them more efficient by sending trucks only when needed," Greenfield said. "The roads get salt when necessary, keeping the roads safe, and no treatment when there is no need for it, which reduces unnecessary damage to bridges, cars and the environment, and reduces the unnecessary expense of treatment."
  
  Bridges typically frost two to three times more frequently than other roadways.
  
  "There are some mornings when you wake up and see frost on everything - from your car to the grass," Greenfield said. "But just because you see it everywhere doesn't mean that there will be frost on the bridge. And sometimes there will be frost on roads but not on bridges.
  
  "That's why it's important to get an accurate computer frost predictor to the DOT."

Tina Greenfield, Jose Alama and Brian Tentigner.

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February 24 to March 9, 2003