With passive sensors, the data is not only collected, but also calculated. This is done by a trough in the sensor that can collect a defined quantity of water. This allows the proportion of salt in the water to be determined exactly, which is then used to determine the freezing temperature. The active pavement sensor detects freezing temperature by actively cooling and heating the sensor surface. It is quite easy to combine passive and active sensors and this is recommended.
Depending on the project and its location, different sensors are used as necessary. Individual sensors manufacturers are often quite specialized and the selection of measuring technology depends on the project and type.
This European standard specifies the terminology and performance requirements for all components of a stationary system within the road condition and weather information system (RWIS).
The term TLS stands for “Technical specification for distance stations” and governs the application-specific data communication from road weather stations. Furthermore, it handles the compatibility of systems among the various functional groups.