Formation of frost on paved surfaces presents a potential hazard to the motoring public in cold climates. Temperatures of the paved surface are not measured routinely by the National Weather Service and are not part of public forecasts of winter conditions, yet highway maintenance personnel must make frost suppression and anti-icing decisions based on expectations of future paved-surface temperatures. The Road Weather Information System measures road surface, air and dew-point temperatures, road surface conditions, and wind data at numerous locations in the state of Iowa and reports the data in real-time to maintenance offices. A model based on simple concepts of moisture flux to the surface was developed that uses data from roadway weather stations or forecasts of dew-point temperature, air temperature, surface temperature and wind speed to calculate frost accumulation on bridge decks in Iowa. The analysis showed that the model has sufficient accuracy to be used as an operational tool for assessing frost accumulation on bridge decks. A logistical regression procedure was developed to determine the probability that a maintenance worker will observe frost for a given calculated frost depth.