Final answer:
A low air pressure warning device must operate at 60 psi and below or half the governor cut-out pressure, whichever is less, to ensure vehicle safety.
Step-by-step explanation:
The low air pressure warning device must operate at 60 psi and below, or half the governor cut-out pressure, whichever is less. This safety mechanism is essential in vehicles, especially commercial ones, to alert the driver of potential air system problems that could lead to brake failure or other risky situations. It's crucial for the safety of the driver and others on the road that this device functions correctly and at the specified pressure levels.