38355.  (a) Except as provided in subdivision (b), every motor
vehicle shall be equipped with a service brake system which is in
good working order and adequate to control the movement of, and to
stop and hold to the limit of traction of, such vehicle or
combination of vehicles under all conditions of loading and upon any
grade on which it is operated.
   (b) Any motor vehicle, such as an air-cushioned vehicle, which is
unable to comply with the requirements of this section due to the
method of operation, is exempt, if the operator is able to exercise
safe control over the movement of such vehicle.