Pavement Temperature vs. Air Temperature

Top Snow and Ice Removal Seminar Speaker Highway & Road Deicer Consultant & Expert Trainer Expert Advice on Pavement Temperature vs. Air Temperature

Typically pavement temperature will move similar to the air temperature and normally with some thermal lag. The curve usually looks like the following diagram with the air temperature changing often rapidly, while the ground temperature follows. Some exceptions to this are noted. This is an idealized diagram and it should be noted that several factors can and do significantly affect the pavement vs. air temperature relationship. The two most significant are subsurface or ground temperature and the presence or lack of solar radiation. The subsurface – if the subsurface is warmer or cooler than the air and pavement it can affect the air-roadway temperature relationship. Two examples: 1. In the fall, the subsurface is still above freezing when the air temperature is below freezing. The reason is that often during these conditions, the cooler air temperature cannot remove enough heat from the roadway surface and the subsurface to drop the pavement below freezing. The pavement is drawing heat from the subsurface. 2. In the late winter or early spring the subsurface temperature is often below freezing while the air temperature is above freezing. In this case the air cannot transfer enough heat to the pavement to offset the colder subsurface. This is especially true with the reduction of solar radiation such as cloud cover and/or shading. Solar radiation –The effect of sunshine can significantly affect the pavement temperature depending on the time of year, cloud cover, shading from vegetation, and the color of the roadway surface. Typically, the darker the roadway surface color the warmer the surface temperature will become. Without the presence of shade, sunshine at times can raise the pavement temperature significantly above the ambient air temperature. Three examples: 1. In the summer under bright sunshine and no shading pavement temperatures can be much warmer than the air temperature, especially if it is new asphalt and is very dark in color. 2. In the winter, bright sunshine on a pavement surface when the air temperature is slightly lower than freezing can raise the pavement surface temperature to above freezing. 3. In the winter, the angle of the sun and the presence of cloud cover can prevent the sunshine from reaching the roadways surface. This allows the air temperature to rise while the roadway surface stays cold. This explains why the air temperature can be above freezing while the roadway surface temperature is at the freezing point of water.

Pavement Temperature vs. Air Temperature by Dale Keep, Highway & Road Deicer Consultant & Expert Trainer