The following is a brief look at the possible significance of trains in dreams. I believe that the symbolism here may also apply to trains used in sandplay therapy.
To see a train in one's dream represents conformity. One may just be going along with what everyone else is doing. Alternatively, a train means that one may be very methodical. One needs to lay things out specifically and do things in an orderly and sequential manner. In particular, if one dreams about a freight train, then it refers to the burdens and problems that one may be hauling around. It is also symbolic of manual labor.
If one dreams of a passenger train, then it relates to mental work. If one sees or plays with a model train in dreams, then it indicates that one may want more control and power over one's own life and where it is headed. Dreaming of trains may also be a metaphor that one is "in training" for some event, job or goal.
To dream that one is on a train symbolizes one's life's journey. It suggests that one may be on the right track in life and headed in the right direction. Alternatively, the dream may mean that one may have a tendency to worry needlessly over a situation that will work out in the end.
To dream that one is in a train wreck suggests chaos. The path to one's goals are not going according to the way one planned it out. One may be lacking self-confidence and having doubt in one's ability to reach goals. If one dreams that a train collides with a car, then it indicates that one's life goals are in conflict with one's belief system. Perhaps one is pursuing a goal that one is not passionate about.
To dream that someone is hit by a train implies that they may be on the wrong path in life. Perhaps one needs to seek understanding to guide them in the right direction. Such dreams may also be a projection of one's own Self. In other words, one may be on the wrong life path and may need to alter course.
To dream that one is the train engineer signifies that one may be in complete control of a particular situation in waking life.