How much overlap is required to be off an Automatic stop signal on double line Automatic block system? A. 180 meters B. 120 meters C. 90 meters D. Zero

180 meters
120 meters
90 meters
Zero

The correct answer is: 120 meters.

An Automatic block system (ABS) is a railway signaling system that uses track circuits to detect the presence of trains and to prevent trains from colliding. In a double line ABS, there are two track circuits, one for each track. The overlap is the distance between the two track circuits. The overlap is required to ensure that there is always a safe distance between two trains on the same track.

If the overlap is too small, there is a risk that two trains could enter the same block section at the same time. This could lead to a collision. If the overlap is too large, it can waste space and reduce the capacity of the railway line.

The overlap is typically 120 meters in a double line ABS. This is the minimum distance required to ensure a safe separation between two trains.

Option A: 180 meters is too large an overlap. This would waste space and reduce the capacity of the railway line.

Option B: 120 meters is the correct answer. This is the minimum distance required to ensure a safe separation between two trains.

Option C: 90 meters is too small an overlap. This would increase the risk of a collision between two trains.

Option D: Zero is not a possible answer. There must always be an overlap between two track circuits in a double line ABS.