REAL TRAINS AND THE IMAGINATION
Much of the traffic handled by train dispatchers is operated by written instructions issued ahead of time by the train dispatcher. Trains are visible to the dispatcher only in the imagination, prompted by reports of stations passed by the trains or reports from the trains themselves. Having received movement instructions, the train will probably not again report to the dispatcher until further instructions are required. Should conflicting instructions be issued, the dispatcher may catch them while in the process of constantly reviewing the instructions issued, and might be able to communicate with at least one of the trains involved. As the route is limited to the available track, contacting only one of the two trains still may not prevent a collision. Trains are extremely heavy vehicles and stopping from a moderate speed of 40 mph could require a mile. View along the track is regularly obscured by terrain and unlike with aircraft, once opposing trains become visible to each other, it is usually too late to avoid collision. When dispatchers have a display of their traffic, the display represents not individual trains, but miles-long sections of track which show as occupied or unoccupied. Failure of signal equipment or even of the track structure itself will result in the same indication on the display as will one or even many trains. The actual location of the traffic still remains within the train dispatcher’s memory and imagination and even momentary distraction can be critical.