Local Routeing Question Tame Bridge

[trainJam]

According to NRE journey planner, tickets (any permitted, not the not via Birmingham) starting from stations between Gravelly Hill and Blake Street appear to be valid via Birmingham New Street.
The NRE routeing calculator says this is a local journey with Birmingham Group routeing point.

Step 3 of the routeing guide says:

Common Routeing Points
If the origin and destination have a common routeing point, the permitted route is direct via the
shortest distance from the origin to the destination over which a regular scheduled passenger
train service operates. No doubling back (passing through the same station twice on a single
journey) is allowed which may require customers to change trains short of the routeing point,
unless an easement allows a longer alternative route.

The shortest distance is changing at Aston.
I can't find any easements about this either.

(1) Why is there (on any permitted tickets) validity via Birmingham New Street?
(2) Is break of journey permitted at Birmingham New Street?

 

[greaterangrier]

Birmingham Routeing Group consists of Aston, Birmingham New Street, and others.

You can travel within the routing group to another station provided that it still follows a shortest route when you snip out the doubleback.

The paper Routeing Guide says in some way or another that this validity is for interchange purposes only implying BOJ is technically not permitted. However nobody can reasonably be expected to dig through heaps of PDFs of non-contractual information to find this.

 

[P Binnersley]

Acording to The National Routeing Guide in Detail (Section F):

Finding a permitted route when the origin and destination stations have a routeing point in common.
If there is a common routeing point, the permitted route is the shortest route or a route which is longer by no more than 3 miles. Also permitted is the route followed by direct trains to and from the common routeing point if the journey is made on those trains.

They give an example of Stratford upon Avon to Solihull being vaild via Birmingham.

But the journey is valid on direct trains from Stratford-upon-Avon to Birmingham and from Birmingham to Solihull. Note, however, that if the same journey is made by trains which are not direct to and from Birmingham, this ceases to be a permitted route.

As there are direct trains from New Street to Tame Bridge Parkway via Soho/Perry Barr there does not have to be any doubling back.