Which box holds the main track authority at a station with a siding?

• A. Box 3
• B. Box 7
• C. Box 4
• D. Box 5

Answer: (C)

The main concept is that the authority over trains on the main track at a station with a siding comes from the interlocking that controls the mainline signals and the turnout leading to the siding. This box protects movements on the through tracks and ensures safe passage when siding movements are possible. In a station layout, the box that includes the mainline approach signals and the turnout to the siding is the one that holds the main track authority, because it governs how trains proceed on the main line and how (or if) they can be routed into the siding. The siding usually has its own control or is part of a separate interlocking, but it does not provide the main-track protection. So the box that controls the mainline signals and the main-line turnout around the station is the main track authority.