“No, the UP didn’t make it to the siding before getting hit.”
So how could he have ‘run a red light’, if he wasn’t on the siding?
Commute ran the red, kept going and ran into the UP train on the main. The switch, as discussed was a facing point, meaning when thrown the UP only could go into the siding. For the commute to enter the siding at that switch he would have had to go beyond the switch, wait for the dispatcher to line it for the siding and then back in. A facing point means the point of the switch faces the train to, or can, use that switch.
The signal the commute ran was next to the mainline and gives authority for a train to occupy the next section of track. In other words the commute would have seen a red signal before it came to the switch for the siding, thus protecting the switch.