Track Warrant Control, a form of main track authority commonly used after the mid-1980’s. The dispatcher issues authority based on a printed form, the crews copy the information on the form and read it back to the dispatcher. The form has a series of lines, each with a specific instruction, the lines are numbered and have a check box on them. The dispatcher will tell the crew to check a box on a line number and then then read that specific instruction. TWC is used in the GCOR rule book, in other rule books a similar system is used, but may have another name such as “Form D” in NORAC and “OCS” in Canadian rule books.