Over one hundred years ago railroad operators realized that a passing train could complete an electric circuit between its tracks and activate a crossing signal automatically. Since then motion detectors and speed predictors have been ...See moreOver one hundred years ago railroad operators realized that a passing train could complete an electric circuit between its tracks and activate a crossing signal automatically. Since then motion detectors and speed predictors have been introduced to. Here are some examples of crossing signals switches in action. Written by
David Foss
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