(1) All signal lamps on private carrier buses must be constructed in conformance with the SAE Standard for "school bus red signal lamps," in effect at the time of manufacture of such lamps, and must:

(a) Be mounted on the front and rear of the bus, above the windows, as high and as widely spaced laterally as practicable but in no case will the lateral spacing of these lamps be less than forty inches.

(b) Be mounted so that the vision of front, signals to the front and rear signals to the rear, is not obstructed by any part of the vehicle from 5° above to 10° below the horizontal and from 30° to the right to 30° to the left of the centerline of the bus.

(c) Have the switch which activates the signal lamps be actuated by movement of the stop signal to the extended position.

(d) Be no switch between the signal lamps and the switch which activates these lamps when the stop signal is extended.

(e) Be a flashing red indicator lamp on the instrument panel of the vehicle which will indicate to the driver that the signal lamps are operating.

(f) Operate through a flasher unit which will cause the front signal lamps to flash alternately and the rear signal lamps to flash alternately at a rate no slower than sixty nor faster than one hundred twenty times per minute. The "on" period of the flasher must be long enough to permit the bulb filament to come up to a full brightness.

(g) Signal lamps must be aimed two inches below level at twenty-five feet and straight ahead. An aiming tolerance of from three inches up to seven inches down and ten inches right or left will be allowed.

(h) 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:

(i) 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

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

(2) Rear turn signal lamp and stop lamp lenses must be amber in color to avoid confusion with signal lamps and the message on the warning sign.