By the time a train driver had seen you and it registered that he was looking at a person standing on the track (about 1/4 second) it would be too late to stop unless he was travelling at walking pace (about 4mph)..
Any train travelling at normal speeds would take between 400 yards and 1 3/4 mile to stop.
These stopping distances are long because of basic laws of physics:-
a) the momentum of a large heavy object moving at high speed; and
b) trains have steel wheels on steel rails so the coefficient of friction is much lower than a car tyre on a tarmac road, therefore it cannot brake by "locking" the wheels or it would slide out of control and take about twice the distance to stop.
A pedestrian hit by a train would certainly suffer serious injury. If it was just a "clip" then the pedestrian would probably get a broken arm and/or shoulder. If it was a hit on more than just a limb then death is almost certain. If it was a full-on hit then death would be inevitable.
If you get your shoelace or anything else trapped in a track fitting then you must immediately pull the shoe off and get away until you are 100% certain that another train isn't coming.
If you are in a vehicle that stalls on the crossing then put it in 1st gear and use the starter motor to get it off the crossing. This will flatten your battery and may damage the starter but it's better than having the car wreaked by a train. If it doesn't get off the line then get out and phone the signalman on the line side phone (or dial 999 if there isn't a railway phone nearby).
A train driver will not be prosecuted and cannot be sued for hitting a pedestrian who wandered or stood on the line in front of the train in normal service unless there were very special circumstances (such as, he was drunk or on drugs and had passed a signal at "danger").