1. Why can a train pulled by a DVT‡ not go through certain platforms at new street but can with a loco? And whats the major difference between them?
2. Why d they have the weirdest path ever - in through solihull - loop out east, back in through new street, out again to the M6 and then into wolverhampton
I will try and get an answer to your first question as I know someone who might know the answer.
As for routes through and around Birmingham
W&S▸ drivers know virtually every way from Leamington to Wolverhampton. Apart maybe from Aston to New Street (Proof House Junction) which is the other leg of the circuit through New Street and the Soho Loop.
I believe on a Sunday they even use the Stour Valley direct from Wolverhampton to New Street.
As other have said Networkrail have cobbled togther paths using different combinations of routes to get them across Birmingham.
One of the of the major problems for W&S is that with the loss of the Snow Hill to Wolverhampton LL,
GW▸ direct route, is that coming from Leamington W&S are forced to go LNW to Wolverhapton either via Coventry or Bordesley (part Midland). If you go via Bordesley there is no way of avoiding New Street if you go via Coventry then you can go via Stechford to Aston and the Grand Trunk. via Bescot.
There is very vague talk of a link from the Soho Loop to the Kidderminster line from Snow Hill where they cross, but don't hold your breath. The other link which was also proposed was from the Midland Derby Line North East to the LNW Stechford Aston Line avoiding New Street. There was to be a station at the junction to be called Birmingham Heartlands which would be a major interchange to relieve pressure on New Street by allowing through passengers to change at Heartlands rather than New Street. Thus it would allow South Coast to NW Cross Countries to avoid New Street and also allow interchange with the SW to NE Cross Countries which will avoid New Street via the Camp Hill line plus local interchange with LNW Coventry, International Wolverhampton trains. There would also have been local services to New Street via the Midland.