chaanakya wrote:I suspect that line would have been cleared ( interlocking disengaged) since Vanachal was given green signal to start. Normally route is cleared once departing train reaches the next station( may not be scheduled halting station).
I would prefer to wait for some more clarity on this "interlocking" business which is mentioned in the news report. My understanding is that a system which i) recognizes a train on a specific line ii) then identifying the vacant line/platform and iii) then setting the route and signals automatically for the next train; does not exist (or else it is very uncommon). There is a system of RRI (Route Relay Interlocking) which is a system where the signal man sets the point of entry and exit, and the system automatically sets an appropriate route. But RRI is not installed at every Junction (or major station), and I don't know if it can take too many independent decisions (like the situation here).
There are of course other "interlocking" mechanisms in place. One is that a Red Signal (Home Signal, Starter, Advanced Starter Signal) would only turn green, if some distance ahead of it is clear of any obstructions. The "home signal" which the guard mentions here is a kind of last point check before trains enter the station platforms. In very many cases it is at home signal that the route (which platform the train would arrive at) is also indicated to the driver. With interlocking in place the home signal cannot be set to Orange or Green, if the track ahead is occupied by the train. The guard says he saw the "Home Signal" at Red, which means that the express train ahead had not cleared the platforms. Naturally he panicked and called the drivers, because his train should have stopped at the Home Signal. In ideal situation, the second express train stops at the home signal, the one currently at the station pulls out, crosses the Starter Signal and moves ahead. Then the home signal can be set to amber/orange and then the second train slowly pulls into the platform. Starter Signals and Advanced Starters are also some times interlocked with the "Block Instrument" using which Station Masters communicate with each other and give the "Line clear".
Station Master Sainthia can still give "Line Clear" to Gadadadhpur Station Master, ordering the 2nd express train to move ahead. The system allows it because the first express train is now reached Sainthia, have been pulled into a platform. He cannot do it when the first express train was actually mid-way (i.e left Gadadadhpur but not reached Sainthia). You cannot find fault with SM Sainthia, as his plan could have been to stop the 2nd express train at his home signal, and then take it in when the platforms are cleared.