As temperatures drop to freezing and below this week, drivers should watch for the unusual appearance of black ice in the Los Altos area.
The California Highway Patrol advises that black ice is hard to see at the best of times and almost impossible to detect at night, and recommends that if ice is forming on your side mirrors, it might be freezing on the roadway, so drive with caution.
Bridges, overpasses and shady roadways can collect patches of frost even if roads in general do not have enough moisture to form ice in most spots.
CHP public information officer Arturo Montiel wrote that if a roadway appears wet but no spray appears to come from vehicles' tires, ice may be present.
He recommended driving cautiously, allowing extra room for braking and stopping, and to avoid sudden braking or turning if you do begin to slide.