Twentieth century manual of railway and commercial telegraphy (1905)
Meyer, Frederic Louis, b. 1875 · Chicago, New York, Rand, McNally & Company · leaf 141
Go Ahead.(Single Track.) Go Ahead.(Double Track.) Stop.(Double Track.) … (Single PART YL LESSON I. Block Signaling.Definitions. Absolute Block — A railway supposed to bedivided into certain sections of a given lengthtermed blocks. No two trains or engines, exceptdouble-headers, are allowed, or are supposed to beallowed, to enter any one section at the same time.…
Telegraph
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