National Routeing Guide
Words in
italics are quotations from the Routeing Guide.
The Routeing Points for Bury St Edmunds are Cambridge, Ely and Stowmarket.
Stansted Airport is a member of Stansted Group Routeing Point.
We need to determins which of Cambridge, Ely and Stowmarket are appropriate Routeing Points for this journey.
To do this, we
compare the fare from that routeing point to the destination with the fare for the throughout journey - it is an appropriate routeing point only if that fare is the same or lower than the fare for the throughout journey from the origin station to the destination station.
All fares comparisons must be made using one of the following single ticket
types:
Standard Open Single (SOS)
Standard Day Single (SDS)
Saver Single (SVS)
Cheap Day Single (CDS)
The OP wants to use a FOR ticket, so in the first instance we compare SOS fares. The appropriate fares are:
Bury St Edmunds - Stansted Airport route Any Permitted SOS £15.60
Cambridge - Stansted Airport route Any Permitted SDS £9.00 (no SOS fare).
Ely - Stansted Airport route Any Permitted SDS £12.20 (no SOS fare).
Stowmarket - Stansted Airport route Not London SOS £19.40
Stowmarket - Stansted Airport route + Any Permitted SOS £44.00
For Stowmarket, we are able to compare SOS fares and this shows that Stowmarket is not an appropriate Routeing Points for this journey. For Cambridge and Ely, we are not able to compare the same fare type. So we must compare SDS with SOS fares. This shows that Cambridge and Ely are both appropriate Routeing Points for this journey.
Permitted routes for Cambridge - Stansted and for Ely - Stansted are both shown on map CN only.
Map CN allows Ely - Waterbeach - Cambridge - Stansted and Ely - Bury St Edmunds - Newmarket - Cambridge - Stansted only.
So permitted routes for Bury St Edmunds to Stansted Airport route Any Permitted are:
Bury - Ely - Cambridge - Stansted
and
Bury - Newmarket - Cambridge - Stansted.
http://www.atoc.org/rsp/Routeing_Guide/