Bill Bolton wrote on 12 September 2009
"Richard J." wrote:
Bill Bolton wrote on 11 September 2009
GazK wrote:

Don't forget the loss of capacity due to increased dwell times loading
a DD train...

Dwell time issue only become significant if the train a significant
percentage of the passenger carrying capacity of the DD train
boards/alights at every stop on the route.

In most systems that doesn't happen, with large boarding/alighting
flows only occurring at a relatively small number of stops along the
route.

This isn't "most systems". It's London, and all 6 of the central area
stations on Crossrail

London isn't as special as you seem to think. 6 stations in a central
area with heavy traffic is nothing particularly unusual for DD train
operations.

I was contrasting it with your "most systems" comment. The point is
that if the stations with the heaviest passenger flows are in the
central section where you want the greatest train frequency, then peak
trains per hour will be limited by the increased dwell times there, as
GazK pointed out. The dwell time issue doesn't go away just because
stations further out from the centre don't have that problem.

--
Richard J.
(to email me, swap 'uk' and 'yon' in address)