On Thu, 9 Jun 2005, Boltar wrote:

The queue in such a situation would be jam all the way back to White
City as that is the next nearest turning point. Reversing trains

I don't know if this is an issue on the central line but it does seem on
some lines that some connects between the running lines have been
removed for no obvious reason , leading to less flexibility in the
service if theres a screw up. Convent garden on the piccadilly line
spings to mind , not to mention the connection at finsbury park being
lost due to the victoria line using an ex-picc tunnel. So if theres a
problem on the line you get huge sections closed. Doesn't seem like a
good situation.

I was thinking about this this morning. Yes, if there were more
crossovers, connections and whatnot, there would be more flexibility in
reversing trains; if lines were signalled for reversible running, it'd be
faster to back them up; if every line had overlap protection, it'd be
faster to get trains past failed signals.

BUT! Every component you add to the system is a new point of failure.

Think about it - what was it that caused the whole Central line problem in
the first place? A set of points! Would you really want to double the
number of points on the line, knowing it would double the failure rate?
Similarly, if you built a fully belled-and-whistled line with all mod
cons, i think you'd find the failure rate was even higher. You'd be able
to deal with the failures better, but it's far from clearthat you'd get an
overall better level of service. Plus, more gizmos means more maintenance
cost, which in practice means a limited budget being spread more thinly,
which drives up the failure rate even more. That's not to say that LU
wouldn't be better off with more gizmos than it has at present, but
deciding the optimal level of complexity is not a trivial problem.

The way out of this conundrum is to add complexity that's fail-safe, so
things that are good when they work don't become bad when they don't work,
they just become nothing. I don't think there's any way to build fail-safe
points, though.

tom

--
The number of Adam's children, as says the old tradition, was thirty-three
sons and twenty-three daughters