Final answer:
The first parts of the road to freeze as temperatures drop are often elevated structures like bridges and overpasses since they lose heat more quickly. Salt is used to lower the freezing point of water on roads, but its effectiveness decreases significantly at very low temperatures. Ice typically forms from the top down, which is pertinent in bodies of water but less so for roads.
Step-by-step explanation:
The parts of the road that are first to freeze as temperatures drop are typically elevated structures like bridges and overpasses. These areas are more exposed to the cold air and can cool down more rapidly than the surrounding ground which retains some warmth longer. Surface ice formation on roads is also influenced by various factors such as material, traffic, and local climate conditions.
Bridges and overpasses lack the insulation provided by the earth, allowing them to lose heat from all sides, leading to quicker freezing in comparison to ground-level roads. Additionally, applying salt to these surfaces is a common method used to lower the freezing point of water, thereby preventing ice formation. However, it's important to note that this method is not effective if the temperatures are significantly below the minimum temperature at which the salt can prevent freeze.
Furthermore, ice forms a protective layer on top of bodies of water which is less dense than the liquid beneath, allowing aquatic life to survive underneath. This principle of freezing from the top down is important in understanding how ice behaves in different environments, but does not typically apply to roads unless they are compromised by water from melting snow or springs beneath the surface.