Central Line Switcheroo.
 

London Underground's Central Line is in effect two
separate lines which share most of the same route.
One service is from Epping to West Ruislip and the
other is from Hainault to Ealing Broadway. Those trains
starting at Woodford and running round the loop via
Chigwell to Hainault, after a few minutes wait go on
to Ealing Broadway.

This afternoon, I jumped on a train at South Woodford
heading for West Ruislip. When we had arrived at
Leytonstone, the driver announced the train was "ready
to depart now for Ealing Broadway."

Clearly there was some re-arranging of trains. I couldn't
see why. In both directions trains were running smoothly
at two minute headways.

I've never known an ex Epping train go to Ealing Broadway
before. Does anyone know how often Central Line trains are
re-routed like this?