Which of the following is most likely to be slippery when wet?

A road is most slippery during the first few minutes of rain after a long dry spell. Oil, rubber, and other contaminants build up on the road surface during dry weather. When water first hits, it mixes with these substances to form a slick, almost greasy film. Once the road has been thoroughly washed by sustained rain, the contaminants are flushed off and traction improves somewhat, though wet pavement is still less grippy than dry. This is why crashes spike in the first 15 to 30 minutes of a rainstorm and why experienced drivers slow down immediately when rain starts rather than waiting for the road to look wet. Bridges and overpasses freeze first and stay slippery longer because they lose heat from both sides.