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". A Clear Block is a condition where a particular block or predetermined length of track is clear of all trains. In addition to the condition of the block ahead, The Standard Code of Operating Rules, such as those still in use on the LIRR, gives one train "superiority" over "inferior" trains. The "superior" train has Right-of-Track over the "inferior" trains. To move the "inferior" train against a "superior" train, Train Orders are used to govern the movement. On this railroad, a compilation of Train Rules such as superiority, and Block Rules such as a "Clear-Block" is used to proceed on the main track.