Bill Bolton wrote on 13 September 2009
02:32:41 ...
"Richard J." wrote:

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

There is clearly a trade off between frequency and capacity, however I
find it very hard to believe that in the Crossrail context the whole
load of a train is going to change over at each of the 6 CBD stations.

Nobody, certainly not I, has said that. You originally referred to "a
significant percentage of the passenger carrying capacity of the DD
train" boarding/alighting.

In practice it doesn't work that way on *any* system and with good
loading vestibule design on DD rolling stock, significant number of
passengers can be handled at each heavily traffic station without the
dwell time impacting the *actual track capacity* in terms of people
moved.

Yes, I agree that you could achieve the same track capacity by using DD
trains at lower frequency with longer dwell times. But that doesn't
necessarily mean that DD trains, with all the resultant extra
infrastructure costs, actually *increase* the track capacity, which is
what this sub-thread is all about.

CityRail does it in Sydney using an all DD fleet without any
particular problems.

If you say so. According to the Sydney Morning Herald in April this
year, "the pricing regulator found last year that the CityRail network
was approaching timetable collapse under the weight of unprecedented
demand as Sydney has grown." What actual train frequencies per track
are currently achieved by CityRail in the CBD? It's not easy to work
that out from the published timetables.

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