On Wed, Jul 20, 2011 at 01:13:40PM -0700, brixtonite wrote:

Didn't mean to complain exactly - the ELL extension to Clapham
Junction will be a huge improvement on what's currently available on
the SLL and I am sure it will be very popular. I just think it's a
shame it can't run to tube or DLR frequencies, and likewise for other
national rail routes in areas not served by the tube.

The trouble is that all those NR routes have lots of junctions, much of
the track is shared between several routes, and some of those routes are
longer distance ones to places like Brighton. This makes scheduling
lots of frequent services Challenging, and means that as soon as one
route goes wrong (like, say, something running late and missing its turn
at a junction) the problems rapidly cascade to lots of other routes. If
you have lots of junctions, you need large gaps between trains so you
can recover better from things like that. A reliable service is better
than a very frequent but unreliable service.

You will note that the Underground lines that have the most junctions
are those that run at the lowest frequencies and have the most
reliability problems, whereas those with few junctions run a much more
frequent and reliable service.

This is why when I grumble about the trains being packed between
Shepherds Bush and Clapham Junction, I maintain that the solution is not
a more frequent service, but longer trains.

SOME of the route conflict problems could be solved by reducing the
number of destinations served from each station, but many of them can't
be because of a lack of good interchanges. Taking just one example and
ignoring junctions further up the line, northbound trains from Thornton
Heath go to Victoria or London Bridge, diverging at Streatham Common.
You can't change that to a single route with a change of trains at
Streatham Common because both routes use the same platforms at Streatham
Common and there is no station at the right place on the line between
Mitcham and Streatham. See he
http://tinyurl.com/3ry5l2u

Streatham Common station is at the bottom, trains to Victoria head
north, trains to London Bridge take the curve from immediately north of
the platforms up towards the top right, where they join the line from
Mitcham (off screen on the left) and Streatham (off screen top right)
stations.

The *ideal* in this simplified example would be to move the station
north a bit and make it easy to change between Streatham Common High
Level and Streatham Common Low Level, getting rid of all the junctions.
Unfortunately in the real world there are other junctions in the area
and you won't get any benefit unless those are done away with too, and
replacing eleventy squillion stations, re-laying track as necessary,
buying and demolishing surrounding buildings - all thise would be
ridiculously expensive and time-consuming. Much easier to just have
longer trains to cope with the capacity problems in the peaks.

--
David Cantrell | top google result for "internet beard fetish club"

The word "urgent" is the moral of the story "The boy who cried wolf". As
a general rule I don't believe it until a manager comes to me almost in
tears. I like to catch them in a cup and drink them later.
-- Matt Holiab, in the Monastery