The reliable detection of water and ice over road surfaces is an important issue in improving traffic safety and reducing costs for the maintenance of routs, especially during winter. A low cost capacitive sensor for the estimation of road conditions is studied. A simulation model was developed to investigate the capacitance of the sensor when air, water, or ice are covering its surface and to assess the effect of the variation of environmental temperature, or of the thickness of water or ice.

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... n algorithm for the estimation of the state of the sensor (dry, wet, or icy) was developed based on the results of the simulations, which indicated that the time derivative of the estimated capacitance provided optimal information. Accuracy and reliability of the estimates provided by the sensor were assessed in laboratory experiments, placing more sensors in a climatic chamber and investigating the estimated state of the sensors and the timing of the identification of wet-icy or icy-wet transitions. Reliable estimates were obtained by all the sensors, with a dispersion of the transition times of the order of a few minutes. The sensor was also investigated in field. Two sensors (one of which was bituminized) were embedded in a road pavement to monitor continuously the road surface condition for a month. Both sensors provided indications in line with the environmental conditions, identifying properly the icy condition and indicating the wet state of the road both during rain and fog. Thus, the sensor is suggested as a feasible tool for monitoring road conditions to support information systems improving security and efficient maintenance of roads during winter.