Positive train control will basically prevent four things: it would prevent over-speed, if a crew is going over the speed limit; it would prevent a collision between two trains; it would detect if a switch is left in the reverse position and would slow down the train; and if there's a work zone ahead of the train and the train is not slowing down because they did not get permission from the foreman to go through, it would slow down the train.
What you would need in order to prevent what you're talking about—trespassing—would be some sort of detection on the track. With 72,000 kilometres of track in Canada, it would be almost impossible. Many of those systems are being tried out throughout the world right now, but an animal will trigger it. There are all sorts of things that may...someone who just goes through very quickly will trigger the system. They are not up-to-date right now.