It is 'possible' for the operator to override the automatic system which controls trains most of the time. (ALL trains are being run slower, on manual today). I doubt it is currently possible for the automatic system to take back control quickly if the operator is careless, falls asleep...etc.....although on regular locomotives, there is a 'deadman' switch' that the engineer has to press every couple of minutes. If he does not, the train automatically brakes and sounds an alarm.

The accident was on a curve, and (just guessing) IF the operator had switched to manual, she might not have seen the stopped train in time. There was one story saying there had been a general 'stop' order sent out from dispatch because of delays ahead. *IF* she switched to manual to stop, then delayed too long...etc...etc....

There will be a LONG investigation to determine whether there was human error involved, problems with automated control...etc.