What are the two types of railroad signals?

Those with a square end are absolute signals and generally force trains to stop when in their most restrictive position. Those with a pointed end are permissive signals and permit a train to continue at a significantly lower speed rather than having to come to a complete stop.



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Railroad signals are categorized into two levels: Permissive and Absolute. Both serve a specific function of either protection or control.

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“Green” is 2 vertical lights & means “clear”.” “Yellow” is 2 diagonal lights pointing up to the right & means “approach.” “Red” is 2 horizontal lights & means “stop.” “Lunar white” is 2 diagonal lights pointing down to the right & means “restricted speed.”

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Active Grade Crossings have active warning and control devices such as bells, flashing lights, and gates, in addition to passive warning devices such as crossbucks (the familiar x-shaped signs that mean yield to the train), yield or stop signs and pavement markings.

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Single yellow means you can pass your train this signal and be prepare to see the next signal , which is not yet clear. And double yellow means the you can pass this signal with your maximum permissible speed , as the next signal is also clear.

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The first movable signal was a revolving board, introduced in the 1830s, followed in 1841 by the semaphore signal. One early type of American signal consisted of a large ball that was hoisted to the top of a pole to inform the engineman that he might proceed (hence, the origin of the term highball).

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