Answer
The bridge is exposed to the cold air above and below, while the road is exposed only above. Also, the road can receive heat energy from the ground, whereas the lower surface of the bridge is in contact with cold air and transfer of thermal energy (conduction) from gas to solid is less than from solid to solid. Thus the water on the bridge could be frozen while that on the roadway is still liquid.
Work Step by Step
The bridge is exposed to the cold air above and below, while the road is exposed only above. Also, the road can receive heat energy from the ground, whereas the lower surface of the bridge is in contact with cold air and transfer of thermal energy (conduction) from gas to solid is less than from solid to solid. Thus the water on the bridge could be frozen while that on the roadway is still liquid.
