An emergency stop button for a robot car shouldn't immediately disengage all other automation and apply maximum braking as the parent comment seems to be implyi

An emergency stop button for a robot car shouldn't immediately disengage all other automation and apply maximum braking as the parent comment seems to be implying. That would, indeed be very dangerous. An emergency stop routine should involve a code path designed to bring the car to a stop in a safe location as soon as practical. It should be thoroughly tested on degraded hardware with minimal branching relative to normal operation. It should also activate the hazard lights, contact the operator's emergency department, unlock all the doors, and lower the windows.