I offer for your consideration the following:

GCOR (General Code of Operating Rules) 5th Edition (Effective April 3, 2005)

Rule 8.4 Lining Main Track Switch states:

"When an employee lines the switch to let a train enter or leave the main track, the employee must then go to the opposite side of the main track and not return to the switch stand until movement is complete. If unable to go to the opposite side of the track, the employee must stand at least 20 feet from the switch stand."

Rule 8.7 Clear of Main Track Switches states:

"Except in switching movements, when a train or engine is approaching or passing on a main track, employee must not go nearer than 20 feet to any main track switch."

"When a train or engine that will be met or passed is on a siding or other track, the employee attending the switch must be in a safe location. The employee must not be nearer than 150 feet, if possible, from the switch when the train is closely approaching and passing."

I'm not inferring that it was the employee at the turnout, especially if they are using spring switches at this location. I'm just suggesting that GCOR can be a valuable resource and if followed will prevent most of the problems that have been encountered historically in railroading. If your operating rules (not TSRR specifically, but all tourist operations) don't include something about this issue, you need to revisit the rule book for an addition or modification.

Rule 8.9.6 Approaching a Spring Switch in Non-signaled Territory States:

A train in non-signaled territory must approach the facing points of a spring switch prepared to stop until:
- A switch point indicator shows the switch is properly lined.
or
- A distant signal displays clear.

Obviously, if a spring switch is at the collision location on the TSRR, all but the last truck of the last car made it safely over the switch points. Not being familiar with the operation, can anyone who is familiar please report on how the switch is indicated, if it is in fact a spring switch?

Now, as a final consideration in the collision,
Rule 6.8 Stopping Clear for Meeting or Passing states:

"A train that may be met or passed must stop at least 400 (four hundred) feet from the signal or clearance point of the facing point switch the other train will pass over, if length of the train permits."

If the siding is long enough and the train short enough, had the train in the siding stopped another car length back from the clearance point, the other train would have stopped before the collision happened. On the other hand, hitting the standing train may have prevented the last car from turning over and dumping passengers onto the track. Maybe it was a fortunate circumstance in that respect.

Again, not trying to pick any fights, but just sharing the GCOR rules as they MAY apply to the incident. I'm looking forward to the official report of the incident.