There is no railway safety appliance that cannot be defeated by a sufficiently clever person In the case of a recent runaway Elevated train in Boston, it's as clever as a length of heavy wire. There's a picture at the link. Do not attempt this when the Grumpy Old Road Foreman is around, or any other time. "The train operator’s public address microphone and cable was wrapped around the controller so as to disable the safety system that would stop the train if an operator’s hand was not present." The motorman, who has since been discharged, had a prior record of reprimands for safety violations. Things ultimately done decently and in order.
I have another post in preparation dealing with the Bad Aibling crash, in which I will argue that the way the train dispatcher defeated several safety appliances was too clever by half.