wrote:

Surely both are possible? As the tunnels are halfway to Camberwell
already, it makes sense to go there, so you could have Elephant -
Walworth - Camberwell - Denmark Hill - Peckham Rye - Nunhead - Brockley
- Lewisham, then all stations to Hayes.

Both are possible, but just being possible doesn't make something the best
option. A tunnel going half way to Camberwell is not a good reason to
extend trains there through it when there is already a railway on the
surface going all the way there and beyond!

South London is quite well supplied with railway lines, so a Bakerloo Line
extension wouldn't be as useful as a mainline loading gauge railway (which
could increase service frequency on existing lines as it would be a useful
alternative to the congested London termini).

Your suggested Bakerloo extension to Camberwell, Lewisham and Hayes
suffers from that problem. Trains with tube loading gauge would not be
able to share the Denmark Hill to Lewisham section with trains of mainline
loading gauge. That would mean more tracks would have to be built, which
would make it much costlier. It would be difficult to add more tracks to
Lewisham station itself (although the benefits of doing so would also be
high) and the Hayes Line would lose its direct service to Cannon Street.
The City is more significant on the Hayes Line than on the rest of the
South Eastern, as people going from Hayes to the West End can get there
more quickly by catching a bus to Bromley South and a fast train to
Victoria, so diverting the trains so far away from it would inconvenience
a high proportion of the passengers. Also, the Hayes Line serves Catford
station, which is very close to Catford Bridge station, which already has
trains to Nunhead, Peckham Rye, Denmark Hill and Elephant. Therefore your
plan would make things worse for many people.

Are there any other options for extending the Bakerloo via Camberwell?
It might be possible to utilize some of the old Crystal Palace High Level
trackbed in a southward Bakerloo extension beyond Camberwell that avoids
the main line, but it is difficlut to see a good reason for doing so. The
land is not very densely developed (and not a prime candidate for dense
development either) and is near a lot of parkland and open space, so you
wouldn't have enough passengers to make it worthwhile. Also, it's not
really that far from other lines. If any of that branch is ever to be
relaid, it would be best to do so as a tram line rather than a Tube line.

'Tis a similar story for other parts of South London that aren't very near
railways. With trams planned to run to Peckham and Brixton, extending
these is likely to be a more cost effective solution than building another
tube line - and there are plans for othe Central London tram lines which
may be built if CRT is successful.

That would probably be a pretty overcrowded branch, and any problems
that may come from trying to create more lines on the Denmark
Hill-Lewisham axis (which is partly in a cutting, I believe).

What's more, the obvious route for the Bakerloo to take to Lewisham
would be down the Old Kent Road, which must be one of the most busiest
bus corridors in the city, with stops at Elephant-Bricklayer's
Arms-Canal Bridge-Surrey Canal Road-New Cross-St John's-Lewisham.

If the trackbed of the Bricklayer's Arms branch had not been built over,
it would have made sense to utilize it. However, as it has, I favour the
following alignment: under Old Kent road (with two or three stations, the
last of which would be where the existing line to Peckham Rye crosses it)
then New Cross Gate, then Lewisham.

It would not have to finish at Lewisham. I think the best option is to
surface at Blackheath to give cross platform interchange, then take over
the tunnel to Charlton. Eventually I'd like to see it extended under the
river to LCY Airport, Beckton Park, and Beckton, with a further extension
to Barking initially operated by the DLR in order to build up passenger
numbers before being converted to Bakerloo Line.

--
Aidan Stanger
http://www.bettercrossrail.co.uk