When the temperature drops to near freezing, it is crucial to know if there is enough de‑icing chemical on the road to keep it safe in changing conditions. This document explains why the amount of chemical measurement of Vaisala Embedded Road and Runway Sensor DRS511 is the most accurate indicator for decision making in road surface treatment.
Road Conditions Change Constantly
Traffic and weather cause constant changes in road conditions. These changes are not straight-forward because each change is affected by several factors. For example, when the road temperature drops below freezing it does not automatically mean that the road is slippery; it only indicates that the road will become slippery if the de‑icing chemical is diluted or temperature continues to drop.
Monitoring Road Conditions
During winter time, roads are treated with de‑icing chemicals to keep them safe. However, the treatment seldom lasts long.
The conditions need to be continuously monitored to make sure that there is enough residual chemical on the road. Road maintenance authorities must have enough reliable data available to decide when further treatment is needed and how much chemical to apply.
Road weather stations provide this data from road sensor measurements. The most relevant measurements are amount of chemical, concentration, and freezing temperature.
Each of these measurements requires that there is a measurable amount of solution on the road. The solution consists of the de‑icing chemical that has been applied on the road and the precipitation that has formed on the road.
Freezing Temperature Measurement
At first glance, out of these measurements freezing temperature may appear to be the most useful observation for decision making. However, the freezing temperature measurement is highly vulnerable to errors.
Road sensors are divided into two categories based on the measurement technology: active and passive sensors. Both measure freezing temperature from a single small-volume sample, which is very small compared to the area.