Section 39-21-18 - Audible and visual signals on vehicle1. Every authorized emergency vehicle must, in addition to any other equipment and distinctive markings required by this chapter, be equipped with a siren, exhaust whistle, or bell capable of causing a minimum sound intensity level of eighty-five decibels. The siren or signal must be mounted outside of the vehicle or in front of the radiator.2. Any authorized emergency vehicle may be equipped with safety strobe lights.3. A police vehicle when used as an authorized emergency vehicle may be equipped with alternately flashing red lights specified herein and a vehicle designated for the use of the adjutant general or the assistant adjutant general may be equipped with a siren, exhaust whistle, or bell specified herein.4. Every schoolbus, except vehicles with a seating capacity of less than sixteen students, must be equipped with: a. Signal lamps mounted as high and as widely spaced laterally as practicable, which must be capable of displaying to the front two alternately flashing red lights located at the same level and to the rear two alternately flashing red lights located at the same level, and these lights must have sufficient intensity to be visible at five hundred feet [152.4 meters] in normal sunlight;b. A stop sign on a control arm that can be activated by the bus driver. The stop sign on the control arm must be located on the left side of the bus, be equipped with a flashing red light, and when activated, extend out from the bus at approximately a ninety-degree angle; andc. Safety strobe lights if the schoolbus was manufactured after July 31, 1998. Older schoolbuses may have safety strobe lights installed.