The culprits are black ice, road frost and bridges/overpasses. All have something to do with the interplay between moisture on the roadway, the temperature and the dew point. The result is unpredictable and immediate slippery driving conditions.
The number one precaution to take if you suspect or encounter any of these conditions is to reduce your driving speed. Observe traffic in front of you and look for indications of vehicles in trouble, such as braking or spin-outs.
Do not use the cruise control feature on your vehicle if there is a possibility of less than ideal roadway driving conditions. And, as always, use your seat belts and child restraint devices.
Black Ice
Black ice is virtually impossible to see on the roadway. It usually occurs during subzero temperatures and is especially prone in areas where there are a lot of vehicles sitting at traffic signals, stopping at intersections or generally moving slowly.
Black ice is created when moisture from vehicle exhaust freezes on the surface of the road instead of being dissipated by wind, the sun's rays or friction from tires. It can happen anytime during the day or night and on concrete or blacktop road pavement.
Road Frost
Road frost can take place when there is a relatively quick "warm-up" after an extended period of sub-zero weather. The wide variation of temperatures draws moisture out of the roadway to the surface where it freezes when it is exposed to the air. The warm rays of the sun, wind and friction from vehicle tires are the natural remedies to reduce or eliminate road frost.
Motorists should be especially alert to this potential condition when there is a warm up of temperatures overnight. The most critical time is from the early hours before sunrise to mid-morning.
Sometimes drivers may be able to actually see the white frost. The road will look shiny under headlights during night-time hours or you may see darker wheel tracks that stand out against the surrounding lighter colored area of the road's driving surface.
Sections of a roadway protected from the sun may have road frost for a longer period of time than areas more exposed to sunlight. Roads with light traffic will also retain road frost longer.
Bridges/Overpasses
Even though the road you're traveling on may be in good winter driving condition, that might not be the case for bridge decks and overpasses. Early morning and late evening hours are prime time for potential slippery conditions on bridges and overpasses.
The elevated structures are subject to a wide variation of temperature and moisture conditions ranging from warmer air circulating underneath-especially for those over water, to more frequent and extreme freeze/thaw occurrences. All of these factors can create very localized frost or icy conditions.
Motorists should be on the lookout for possible advanced warning signs on the roadway indicating potential slippery conditions on the upcoming bridge or overpass. The best approach when driving on these structures is to slow down and maintain an even speed--do not brake or accelerate while on the bridge or overpass.