If you’re a regular commuter in the Mumbai locals, and you happen to travel on the western line till Borivali in a Borivali fast train, you will notice that many a times, the local trains reach Andheri station and wait for a while, and then switch tracks and move to track 1, which is for slow trains.
Wondering why sometimes the fast trains move to track 1 and do not continue on track 3, and at times continue on track 3?
Its simply because of the train behind your train. For example: If you take a 8:24pm Borivali fast train from Marine Lines station, your train will run on Track 3 till Andheri, and then switch to track 1, because behind the Borivali train is the Virar fast, leaving Marine Lines at 8:27pm. The Borivali train in turn makes way for the Virar fast.
If you happen to take the 8:33pm Borivali fast, you train will continue on track 3 after Andheri station too, because the next train, 8:41pm, leaving Marine Lines is a Virar fast but it becomes a slow train after Andheri station.
Why can’t it be planned in such way that borivali fast local is scheduled after virar fast, so that borivali can go right on track 3 upto borivali. Also many trains on both track 2 and track 1 are held up because of track crossing by a borivali fast local.