The stop signal required on private carrier buses must:

(1) Be fourteen inches vertically and eighteen inches horizontally.

(2) Be treated with red reflective material.

(3) Have the word "stop" painted on the sign in white with letters which are a minimum of eight inches in height and having a three-quarter-inch stroke.

(4) Meet the requirements outlined in above on both sides of the sign.

(5) Be mounted on the left side of the bus just below the window line and adjacent to the driver of the bus.

(6) Be hinged at the front edge of the sign.

(7) Be manually controlled by the driver of the bus.

(8) Be so constructed as to lock in an extended position perpendicular to the side of the bus and to also lock in the closed position parallel to the side of the bus.

(9) Only be actuated by the driver of a private carrier bus whenever such vehicle is stopped on the highway for the purpose of receiving or discharging passengers, except:

(a) When the passengers boarding or alighting do not have to cross a highway and the bus is stopped completely off the main traveled portion of the roadway; or

(b) When the bus is stopped at an intersection or place where traffic is controlled by a traffic officer or official control signal.