That is extremely dangerous. I'd take some photos, arrange for the police to meet them as soon as possible. If not, I'd at least take the photos to the police and report the trespassers if they did it again. I'd certainly shout down to them to get off the line! How are they to know a 156 won't come round the next bend at 40mph? NO chance of survival for them, no chance of stopping for the driver, equalling a big mess, incident and line closure for at least the rest of the day, with probably TSRs and drivers being warned to go slower around the site of the incident. Then of course there's those who are on the train, who'd have to be de-trained and moved on somehow, bit difficult in the middle of nowhere. Don't forget the poor souls who'd have to pick the flesh off the coupler, unit's curves, track and lineside, as well as councelling for the poor driver, who'd probably want to quit driving forever after unintentionally ending at least one life.
Hopefully my point is obvious, but just in case this, and the hundreds of posters all over the network don't make it obvious enough:
STAY OFF THE RAILWAY! If you go on it, you are TREPASSING, which is ILLEGAL. If caught, you'd end up with a criminal record if nothing else. Of course you COULD end up dead, splattered across the line and train. In which case, you'd damn well deserve it.
I can not, and will NOT, condone crossing the line illegally for any purpose. Wouldn't you rather be alive with a good shot rather than dead with a messed-up shot and several lives affected? I know I'd rather be alive! There's no shot worth taking such a risk for. Not one.
Once again, STAY OFF THE RAILWAY! What other advice will you listen to?