(1) interlockIn order to ensure the safety of driving, it is necessary to establish a certain mutual restriction relationship between the signal machine, the switch and the approach. If the switch cannot be moved after the guard is opened, this mutual restriction is called an interlock.(2) closeThe path by which a train or shunting train travels from a specified point to another specified point is called an approach.(3) signal blockThe so-called blocking refers to the use of signal equipment to divide the railway line into physical or logical blocking areas artificially, so as to meet the requirements of safe traffic spacing and improve the transport efficiency.