These men indicated, by means of hand signals, the state of the track ahead.

Trackside control also developed slowly with the first signalman, or “railway policeman,” located at passenger and goods depots, or stations, sited along the line. Engines were fitted with brakes and, later, manned brake vans, whose guard could apply the brakes when the engine driver signaled with a whistle. The smooth contact between tracks and iron wheels allowed higher speeds and greater loads to be hauled at the same time that the low friction necessitated long stopping distances. It was only after the development of swifter steam-driven trains, in the early years of the 19th century, that more frequent trains and their proximity to each other created dangers of collisions. The first slow and cumbersome horse-drawn rail traffic posed few control problems not resolved by follow-the-leader principles.

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Train traffic control unblocked