There are a few ways that a train can end up stopped on a block brake:
1) Blocking violation.
If the next block isn't clear, the train will stop on the block brake automatically. The same is true if a sensor fails and the control system merely *thinks* that the next block isn't clear.
2) Loss of electrical power.
In the absence of electrical power, the brake system will revert to the "set" position, which will stop the train when it arrives.
3) Loss of air pressure.
In the absence of air pressure, the brakes won't open.
4) E-stop.
On most rides, when the operator hits an E-stop button, electrical power is disconnected from all systems on the ride. See "Loss of electrical power," above.
5) Ride stop.
Some rides have a 'clean' Ride Stop feature, which will stop the lift and allow the trains to proceed through the course to cascade onto the brakes closest to the station. See "Block violation."
Getting back to the original topic...
I've never seen a *coaster* with any switches on the safety belts, and I have never seen any coaster with any train telemetry on it once it leaves the station (except for pedal counters which are sometimes positioned on the lift). If an unbuckled safety belt results in a stopped train, it's a pretty safe bet that a sharp-eyed ride attendant who is watching for exactly that kind of thing is responsible for it.
--Dave Althoff, Jr.