"Graham Harrison" wrote

I was also asking about the capacity of the tracks approaching Marylebone.
While DD trains can add capacity without needing to change signaling there
comes a point when (if traffic continues to grow) more trains are
required. How close are the tracks into Marylebone to capacity given
existing signaling etc?
There are 17 arrivals at Marylebone in the peak hour (0757 - 0857). Six
platforms could handle more than this - Charing Cross has around 28 arrivals
in the peak hour, also in six platforms. While the disused tunnels from
Canfield Place could potentially provide additional capacity I don't think
it would be feasible to provide additional tracks between Neasden South
Junction and Canfield Place, so 20 arrivals is perhaps the maximum
practicable capacity. However, with platform lengthening at stations along
the Chiltern Line (some of which is planned or in hand) most trains could be
lengthened - five of the six platforms can take 8 coach trains, though
alterations would be needed to get the remaining platform beyond 5 coaches.

Peter