Engine of stationary vehicle to be shut off

The driver of every motor vehicle shall, when the vehicle is stationary otherwise than through enforced stoppage owing to the necessities of traffic, stop the action of any machinery attached to, or forming part of, such vehicle, so far as may be necessary for the prevention of noise: Provided that this regulation shall not apply so as to prevent the examination or working of the machinery attached to, or forming part of, a motor vehicle where any such examination or working is rendered necessary by any failure or derangement of the said machinery or where the machinery attached to, or forming part of, the vehicle is required to be worked for some ancillary purpose.