manual block signal造句

Separate Manual Block signal aspects existed as well.
Some railroads, notably the Pennsylvania Railroad ( PRR ), had a system of manual block signals activated by wayside operators in stations or interlocking towers eliminating the need for some trains to stop.
This is a form commonly used on railroads such as the LIRR which base its rules on the SCOR . At locations where a " Block-Limit Signal " is displayed in place of a fixed manual block signal, train crews obtain a Clearance Card Form K over the radio or telephone from the operator in charge of that territory, which allows that train to pass that Block-Limit as though it displayed a " Clear-Block ".
It's difficult to find manual block signal in a sentence. 用manual block signal造句挺难的