61-9-308. Two means of emergency brake operation. (1) A towing vehicle, when used to tow another vehicle equipped with air controlled brakes, in other than driveaway or towaway operations, must be equipped with two means for emergency application of the trailer brakes. One of these means must apply the brakes automatically in the event of a reduction of the towing vehicle air supply to a fixed pressure that may not be lower than 20 pounds per square inch or higher than 45 pounds per square inch. The other means must be a manually controlled device for applying and releasing the brakes, readily operable by a person seated in the driving seat, and its emergency position or method of operation must be clearly indicated. The manual means may not be arranged to prevent operation of the automatic means. The automatic and the manual means required by this section may be separate.
(2) A towing vehicle used to tow other vehicles equipped with vacuum brakes, in operations other than driveaway or towaway operations, must have, in addition to the single control device required by 61-9-309, a second control device that can be used to operate the brakes on towed vehicles in emergencies. The second control must be independent of brake air, hydraulic, and other pressure, and independent of other controls, unless the braking system is so arranged that failure of the pressure upon which the second control depends causes the towed vehicle brakes to be applied automatically. The second control is not required to provide modulated braking.