"David Fairthorne" wrote in message
om...
Trains should run at the same minutes past each hour in the regular
off-peak periods. But should the same "clockface" timetable continue
throughout the peak periods? The Strategic Rail Authority seems to
like the idea, but in my opinion they are misguided.

My main reason is that whenever peak-hour extra trains are added to
the regular trains, in order to provide needed extra capacity,
passenger loads will (as a general rule) be unevenly distributed
between trains.

This is what they do on many S-bahn networks.
The lines cycle within a 20 minute period [1] and all paths are
used in the peaks. Historically, in the off-peak they missed
out every other train for a (annoying) 40 minute frequency.
However, as off peak loadings have increased many lines
require two trains per hour and in order to avoid re-pathing
all the trains they run 2 out of 3 in the normal paths with 20
and 40 minute gaps.

From a customer pov it sucks, from an operation pov it's
much better.

tim

[1] Yes I know, there are some networks that cycle on
a 30 minute frequency.


Consider for example the case where the regular service is four tph,
to be supplemented by two extra tph needed to prevent overcrowding in
the peak period. If the regulars run at 00, 15, 30 and 45 minutes past
the hour, when should the extras run? If they were inserted between
regular trains, say at 22 and 52, there would be irregular intervals
and unbalanced loads, so some trains (in this case the 15 and 45)
would still be overcrowded. It would be better for the peak period
trains to run at 00, 10, 20, 30, 40 and 50 minutes past the hour,
meaning however that the 15 and 45 regulars would not run in the peak
hours.


A less common reason to deviate from the regular timetable is to
divide the peak hour service into stages, in order to provide
longer-distance passengers with a faster service and to make more
intensive use of rolling stock. In a two-staged timetable, a fast
long-distance train is immediately followed by a slow short-distance
train. Peak hour staging prevents the regular service from running.

Any opinions and insights concerning this subject would be of
interest.