My wife was riding Caltrain a couple years back when she saw some kids standing on a stack of ties (on the ROW) throwing rocks at the train. She quickly found and told a conductor, who radioed it in. By the time they got to Diridon the conductor came back to her and thanked her, saying the cops had arrested the kids. Luckily, the only damage was some extra dents in the sides of the cars. I started looking at the cars afterwards, and noticed that most of them had some serious dents on them. Guess the rock throwing is still going on these days.