Cool catch - all my years riding by and I never saw anything use those Oak Grove tail tracks.
My understanding is that the tail track was cleared out and made usable in particular for the Oak Grove platform work. With one track OOS at the station, they wanted the tail track to be open to hold a disabled train if needed, in order to keep the station open until it could be removed.
Wondering if I'll see the Haverhill double-tracking finished before I retire... Photo: Melbourne W7 No. 1019 on Route 78, Bridge & Church Streets, Richmond, Victoria. 10/21/2010
Currently, the tail track is barrier free on the outbound track only. There is an emergency exit that crosses at grade on the inbound side. The track is useable but requires the movement of two gates. I have not seen the tail track used since 2004 around the time of the DNC for revenue equipment.