connecting the region ~ Thameslink & Crossrail ~ London 2001
When London's railways were originally
built, they were prevented from crossing the central part of London,
which is why today's city has a multitude of rail termini and no
through train services. The Victorian solution to this problem was the
London Underground, which allowed this rule to be broken by putting the
lines where nobody could see them, and today's Metropolitan Line was
originally constructed to carry through trains from the Great Western
Railway into the City of London.
In 20th century Paris, faced with an
overcrowded and badly maintained underground system, and a lack of
through journey opportunities through the city centre, a similar, and
yet radically different solution was proposed. A number of commuter
lines were extended and joined together through new tunnels under
central Paris, and the network was known as the RER, or Reseau Express
Regional (Regional Express Network), now operated by SNCF Transilien.
Many in London looked on enviously, as one
of the advantages of the RER was quicker and easier transfers between
mainline stations, something which is a major problem in London today,
as well as elminating a change from train to underground for a number
of commuters.
One of the underground lines to cross the
City was the Snow Hill tunnel, which lay almost disused as a freight
line until 1988, when Thameslink was opened, which joined together
services along the Midland Main Line to the north, to the Brighton Main
Line to the south, and enabled through trains between Bedford and
Brighton. This proved immensely popular, so much so that Thameslink
became one of the most overcrowded lines in the South Eastern rail
network. Since the original Thameslink opening had only been a matter
of refurbishing and electrifying an old tunnel, a larger project was
hatched, called Thameslink 2000. [link to TPfLA TL2k page]
At around the same time, British Rail and
London Underground jointly proposed Crossrail, a new underground tunnel
connecting the Great Western Main Line at Paddington with the Great
Eastern Main Line at Liverpool Street. Again, this was to be a commuter
line carrying passenger trains between Reading and Shenfield, and was
due to open in 1999. Here there was more success, driven by a vastly
positive cost-benefit (a cost-benefit ratio of up to 2.5 in some
analyses), as well as the growth of Heathrow Airport and proposals to
link to the still expanding Isle of Dogs area in the Docklands. A
company, Cross London Rail Links Limited, was formed in 2002 to take
the scheme, now called Crossrail Line 1, forward.
Cross London Rail Links' second project
would be a revival of a London Underground plans for a line to connect
Wimbledon and Hackney, via Chelsea, and open up new central London
journey opportunities as well as connecting areas of the capital poorly
served by rail. Crossrail Line 2 is still in discussion, but is likely
to connect Clapham Junction to Hackney along the London Underground
route, and provide a much needed link between the south London rail
network and Kings Cross and St. Pancras stations, with services to the
North and Midlands of England, and soon Paris and Brussels.
This map shows Professor Peter Hall's (head of the Bartlett School of Planning at UCL) plan for a London RER in the 1988 book "London 2001".
Ignore the Jubilee Line (obviously, as it was built differently, but there is a set of points and a stub at North Greenwich which could enable a connection to the Dartford Loop in the future, using suitable trains of course).

This is what is said in the book about the lines. Remember this was written in 1988.
Line 1, the Waterpool Line would hook up BR's shorter-distance Windsor Line services (including the Hounslow loop, Shepperton and Windsor lines, and the Kingston loop), via Richmond and Putney, with the Waterloo and City Line. Via a new transition north-east of Clapham Junction, trains would descend into tube via stations at Battersea, Chelsea (King's Road), Sloane Square, Victoria, and Millbank (Lambeth Bridge), to Waterloo. Thence the Waterloo and City Line would be reconstructed - as already planned by BR - with a new interchange station at Blackfriars. From Bank the line would be extended to a sub-surface station under Liverpool Street.
Thence it would divide. The main branch would take in all the stopping services of the Hackney Downs Line to Enfield Town, Cheshunt, and Chingford. (Direct services via the Lea Valley route to Broxbourne and beyond would continue to terminate at Liverpool Street.) The other branch would take in the old Broad Street Line to Dalston Junction, thence joining the North London link tracks eastward via Hackney central to Stratford.