Chiltern have announced the date when the new service will open west towards London Marylebone from Oxford Parkway and Bicester: 26th October 2015, approx. 7 weeks later than previously proposed (5th September).
The date for reopening service into Oxford seems to be anybody’s guess, given that planning approval has only recently been granted for the construction of two new platforms at Oxford station, lengthened to accommodate the new trains. (This requires the demolition of the building which used to be the post office depot.) No reliable date is available for the completion of the Oxford Area Remodelling project, which will renew the track layout north of the station and replace signalling.
It seems likely that tunnel, bridge and track work on the line will be complete long before Oxford station is ready. Chiltern will obviously have difficulty running the new service into Oxford without the modifications necessary for a half-hourly additional service to London with appropriate rolling stock. Even were it possible, the service would be prone to much disruption as work progresses and congestion occurs.
OBRAG has proposed running a reduced shuttle service with a two-car train, similar to the old service in this period. This would eliminate disruption to the mainline service, while allowing Islip and Bicester commuters to resume access to the city of Oxford without slow and unreliable buses. It would also spare Chiltern the expense of running ‘bustitution’.
I will add their response here when it arrives.