(1) "Chief" means the chief of the Washington state patrol or their designee.

(2) "Private carrier bus" means every motor vehicle designed for the purpose of carrying passengers used regularly to transport persons in furtherance of any organized agricultural, religious, or charitable purpose, and having a seating capacity for:

(a) Eight passengers if the transportation is provided for compensation; or

(b) Fifteen passengers if the transportation is provided not for compensation.

Such term does not include buses operated by common carriers under a franchise granted by any city or town or the Washington public utilities commission.

(3) "Stop signal" means a sign bearing the word "stop" which is actuated by the driver of the bus.

(4) "Signal lamps" means red lamps mounted on the vehicle to be used in conjunction with the "stop signal" when the bus is loading or unloading passengers under certain conditions.

(5) "Warning sign" means a sign to be attached to the rear of the bus to inform following motorists of their duty to stop when the "signal lamps" are activated.