Any person who has driven on a cold New Mexico night is aware that bridges usually freeze before the rest of the road (some have learned this the hard way). The primary goal of this project is to understand heat conductivity through a bridge, and determine why the roadway on a bridge freezes before the road directly in the ground. The secondary goal is to design a computational model that can determine under which conditions a bridge may or may not freeze.

This simple question, “On a cold night, why does the bridge freeze before the road?”  requires sophisticated physics to answer. There are a variety of considerations for such a model. What is the starting air temperature? What materials are used for the bridge? What is the heat capacity of each of these materials? To create an effective model we used a uniform concrete suspension bridge parallel to the ground. We assumed that the starting temperature for the bridge and ground would be the same, and the starting temperature for air would be varied. We additionally, examined the sensitivity of the system to different base conditions.

Using the principle of conservation of energy, we derived a system of equations to model heat diffusion on both level road and suspended bridge. This model incorporates the scientific principles of conduction and radiation to calculate unit temperatures after successive day-night cycles. The graphical interface allows the user to isolate the temperatures of individual parts of the bridge in order to determine the cause of early freezing.

The model reproduces a real-world situation: material coefficients are based on existing thermal data and the model can be effectively applied to real-world bridges in cold climate areas which are subjected to freezing temperatures during the night. This model has the potential for use by meteorologists, police and transportation safety officials to accurately predict when travel conditions have the potential to become unsafe in certain areas. The diffusion code can be easily adapted to a variety of applications such as cellular osmosis and building efficiency and also the potential for a multitude of other uses.