"You should avoid cars with only one door open, because the pin may break, locking you in. A car with both doors open gives you one free chance. Pig-backs (trailers on flatcars) are generally considered unsafe. Most trains make a number of short hops, so if time is an important factor try to get on a "hot shot" express. A hot shot travels faster and has priority over other trains in crowded yards." - Abbie Hoffman, 'Steal This Book'.