Road temperaturesOur decision to salt routes is taken mainly on weather forecasts, current conditions and road temperatures (rather than air temperature).
You may wake to find your car is covered in frost and the road has not been salted. The temperature of the air isn't a good indicator of road temperature.
In Autumn the road is often kept warmer than the air as the earth retains the heat from summer. In the spring the reverse can be true and the road is colder than the air due to the earth being cold from winter.
Additionally, bridges tend to cool quicker as they are exposed and deprived of ground warmth.
Air and road temperatures can differ by as much as 10 degrees centigrade.