(a) The driver of a vehicle on any curve may not turn to go in the opposite direction if the vehicle cannot be seen by the driver of any other vehicle that is within 500 feet and approaching from either direction.
(b) The driver of a vehicle on or approaching the crest of any grade may not turn to go in the opposite direction if the vehicle cannot be seen by the driver of any other vehicle that is within 500 feet and approaching from either direction.