To be somewhat less charitable, and I’m not directing it towards you, they’re also there so the operator doesn’t sneak off for a cigarette while the ride is in motion.
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Locomotives have a deadman switch, the operator is suppose to keep his foot on a pedal. This is to prevent a run away train in case said operator is disabled.
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Most trains now have modernized that into a “vigilance” control where the system periodically puts up messages like “Press Button A” or “Adjust the throttle” to ensure the engineer is still there, awake, and paying attention. (I don’t know the actual messages, as I’m not a railroad engineer, but that’s the general concept.) This scheme also makes the “Toolbox on the pedal” plot device as used in *Silver Streak *and *The Taking of Pelham 123 *impossible.
I always assumed he had a pneumothorax, but blood in the lungs or hemothorax or shock are all good possibilities.
I understood the purpose of the “deadman’s switch” was to give his allies time to leave AND to give the SWAT Team time to get out, too, if he lasted long enough, but also make sure that the detonator would eventually go off with no opportunity for defusing the explosives.
I’m sure he would have dropped the weight if the SWAT officer had tried to knock it away. IMO, if I were holding that weight in such extremis, even if I didn’t object to you knocking away the weight it would be very likely (or at least, not unlikely) that the weight would fall on the trigger due to tumult and my frailty.
Nowadays this is often a button on the dashboard, that must be pressed every so many seconds (which in some systems can be made dependent on the train’s speed or route or other information) or else a warning then emergency brake application occurs. Since you have to press and release at timed intervals it helps to make sure you’re awake, and you can’t just put something on top of it. Sometimes movement of other controls (throttle, brake, etc.) count as events to reset the timer.
In the original The Taking of Pelham 1-2-3, a big deal is made about how there must**** be someone driving the train, since it has a deadman’s switch. Eventually Lt. Garber comes to the conclusion that the hijackers must have figured out a way to defeat it (which they had, using a tubular brace to hold down the switch).
For the record, he wasn’t holding a ‘weight’ over the detonator switch. It was actually a piece of the large mock-up model of the original Terminator’s CPU, the linked-cube neural-net thing.