fog line

noun3

1. •
   A line painted on a road (usually bright white) that marks the edge of the legally drivable portion.

   • As the driver of the vehicle reached into the glove box to obtain the insurance information another westbound vehicle crossed the fog line traveling onto the north shoulder of the roadway. — 2003
2. •
   The boundary of a body of air, contacting the earth's surface, that has fallen below the dew point and usually contains fog.
3. •
   A division in altitude above which fog appears.

   • Along the coast Sequoia sempervirens does not grow above the altitude to which the moist sea air generally rises — the fog-line, as it is often called. — 1895