Paul Terry wrote:

II've never understood how more trains could be projected down the line
between Barnes and Twickenham, given the frequency of the existing
services and the constraints of three level crossings on the way.

Would it mean diverting the Windsor service round the Hounslow loop -
and would that in any case free up enough slots?

This will be part of the consideration that bidders for the SWT
franchise will have to make.

There is also the question of freight to consider as the West London
Line is increasingly occupied by new passenger services


http://www.tfl.gov.uk/rail/downloads...ve-summary.pdf

A number of us have argued in the past for the diversion of the twice
an hour Reading to Waterloo services to run via Heathrow to Paddington
initially by linking with the Heathrow Connect service thereby needing
no new train paths. This could eventually feed into Cross Rail.The
freed paths from Staines High Street to Waterloo could be taken by
extending two of the four Heathrow Express services to Waterloo - where
the Eurostar terminal becomes vacant. IIRC Siemens Desiro stock works
happily between Paddington and Heathrow already on 25kv and also on
750v DC to Reading from Waterloo. The West Coast mainline Desiros have
both pantagraphs and third rail beams - having been diverted from SWT -
so I assume that the operation of dual voltage trains meeting Heathrow
and Crossrail Tunnel standards would not present at least one
manufacturer with overwhelming technical difficulties. The number of
level crossings could well be an issue. The need to lengthen platforms
to accomodate ten-twelve car trains also needs to be considered.