MEMPHIS, TN (WMC) - When driving over a bridge you might notice a bright yellow sign with black letters. Usually it says, “Bridge Ices Before Road”. Have you ever wondered why this is the case, why will a bridge freeze before the road attached to the ground?
In this episode of the breakdown, we explain the reason why when driving and inclement weather is taking place, you should take extra time on the bridges and overpasses.
Let’s say it is a cold and rainy day. Temperatures may quickly drop below freezing and then ice may form on bridges and overpasses.
Once reason is due to the fact that the freezing wind is blowing both over and under the bridge or overpass, so it is losing heat from both sides, unlike roads on the ground who have heat trapped below the road and only loses the heat from just one side.
Bridges really have no way to trap the heat, to it will freeze quicker and reach the same temperature as the air temperature outside.
Bridges and overpasses are now built with steel and concrete, which are both good heat conductors. Due to the fact it conducts heat, the heat that the bridges have will move through the bridge to the surface where the heat is lost thanks to the air flow around it.
Roads are mainly made of asphalt, which is a poor conductor of heat, and that lessens the rate of heat loss, meaning the road will stay above freezing for longer.
The main thing to take away is that bridges will usually follow the air temperature very closely. If the air temperature is falls below freezing, then you should assume the bridge is below freezing.
Rain or snow will freeze and stick to the bridge. When that occurs, transportation departments advice motorists to slow down when approaching a bridge or overpass in cold weather.
A lot of the time, you cannot see the ice on the road our could be hidden by other forms of winter weather.
If you feel your car “floating” on the road, you should gradually slow down to main control of your vehicle. Never slam on your breaks.