Some urban mass transit coaches are fitted with a brake and accelerator interlock. What does it do, and how should a driver treat it?

Explanation

A brake and accelerator interlock keeps the brakes on and the throttle at idle for as long as the rear door stands open, releases both once that door is shut, and must never be treated as a substitute for setting the parking brake. The distinction matters because the interlock is a convenience tied to one door's position rather than a brake the driver has deliberately set, so it disengages the moment the door closes and leaves nothing holding the bus if the driver assumed otherwise. 49 CFR 383.117(a)(6) covers operating practices and procedures not otherwise specified, and no federal requirement for such an interlock was found: 49 CFR 571.217 is a manufacturer-facing bus window and emergency-exit design standard that does not address it, and 49 CFR Part 38's interlock requirement is for mobility-aid lifts under the accessibility specifications, a different device, so this is attributed to the manual. The wrong options reverse the direction of the interlock or overstate it, making it an automatic parking brake, a door lock that waits on the parking brake, or an engine cutoff, and the first is the specific misunderstanding the guidance warns against.

Source: 49 CFR 383.117(a)(6)