I recently responded to the consultation on the Transport for West Midlands Rail Investment Strategy 2018-47. The strategy hardly mentions future electrification, only specifying Lichfield to Burton-on-Trent for any extension of the cross-city line to Burton. I commented that: 'The strategy should commit to electrification of all major local rail routes for operational and environmental benefits. Air quality concerns at city centre stations, particularly Birmingham New Street, and likely new legislation on air quality, should encourage commitment to reduce and ultimately eliminate diesel passenger trains in the West Midlands region'.
I can see gradual electrification of most non-electrified WM lines on the back of other schemes:
1. Chiltern electrification, being talked up for when it's fleet replacement time. That could kickstart Snow Hill lines electrification-to Stourbridge at least I'd hope, preferably Kidderminster.
2. Chiltern would also mean that Leamington-Banbury, a big chunk of the 'electric spine' would be done. By then Didcot-Oxford should be electrified, so add in Oxford-Aynho Junction and Leamington-Coventry-Nuneaton to complete the Reading to West Midlands electrification.
3. Optimistically hoping that full Midland Main Line electrification to the East Midlands and Sheffield is reauthorised at some point in the 2020s (regardless of HS2 and the electrification to Chesterfield/Sheffield for that), and Derby to Birmingham electrification would be a logical addon. Also hoping by then Northern Powerhouse will have electrified Leeds-York and Sheffield-Doncaster/Wakefield. Cross-country trains could then be electric from Scotland to Birmingham and Reading, or bi-mode for non-electrified bits and from Bromsgrove to Bristol and beyond.
4. Any electrification from Felixstowe/Ipswich to Peterborough, Leicester and Nuneaton for freight should be extended from Nuneaton to Birmingham. Wolverhampton-Shrewsbury should be electrified to complete the regional routes from New Street. Bi-modes for services from Birmingham to Wales.
5. Difficult to see electrification to Worcester/Hereford any time soon, although any electrification from Bromsgrove to Gloucester and Westerleigh Junction should surely include the Worcester loop, and from Droitwich to Kidderminster or whereever Snow Hill lines are electrifed to. Also, while the short single track line from Hatton to Stratford-on-Avon could be electrified with Chiltern/Snow Hill lines, the route via Henley in Arden is harder to justify for the wires, at least south of the higher frequency limit at Whitlocks End. But bi-modes or battery hybrids can plug these gaps.
The short answer to New Street pollution is: bi-modes for Cross Country, and for Virgin to stop the mad use of Voyagers from London to Scotland.