Final answer:
Bridges and overpasses often freeze first when wet due to their exposure to colder air from all sides, causing them to cool more rapidly than regular roadways.
Step-by-step explanation:
Bridge decks and overpasses are typically the roadways that freeze first when wet. This is because they are exposed to the air on all sides, causing them to lose heat more rapidly than roads that are insulated on one side by the ground.
In physical terms, the thermal conductivity of the structure in relation to the surrounding air and ground plays a role in the rate of heat loss.
Other factors, such as the absorbency of the pavement, also affect how quickly a road freezes. Darker pavements tend to absorb more heat and can thus melt ice more efficiently during daylight hours when the sun is shining.
When it comes to maintaining safe driving conditions during winter, many regions use salts such as NaCl (sodium chloride) or CaCl₂ (calcium chloride) to lower the freezing point of water, effectively melting the ice and snow on roadways.
A saturated solution of these salts has a lower freezing point than pure water, which makes them effective for preventing ice formation.
For instance, knowing which salt to use can be deduced by calculating the freezing points of saturated solutions of NaCl and CaCl₂ and comparing their effectiveness at sub-zero temperatures.
Increased friction is desired in many situations beyond just winter tires over icy roads. An example where more friction is desirable includes athletic shoes on a basketball court, which helps the athlete avoid slipping while moving quickly.