South London constraints

Geoff Hobbs is right to draw attention to the massive population increases forecast to hit London in the coming decades, and to focus on the ability of the south London rail network to contribute to the solution to the heavy burdens that will be placed on public transport ( Open Access, RAIL 801).

It is to be hoped that the new London Mayor will carry out an extensive examination of the capability of all public services - not just transport - to cope with the increased pressures, and to deploy brakes or constraints to the population growth if it is found that services will be unable to cope.

In this context, it is vital that service providers do not present over-optimistic assessments of what is possible.

Geoff lists several worthy initiatives that should help with capacity enhancement, but he has fallen into the same trap as many before him (including Network Rail’s chief executive) in believing

that signalling enhancements can produce significant additional capacity on a complex suburban railway.

I can readily believe that on lines such as the Jubilee and Victoria Lines, where there are few (if any) junctions and where every train travels at the same speed and stops at the same stations, some 15% additional capacity has successfully been delivered by signalling enhancement.

But on the south London network, the existing signalling can deliver all the plain line capacity that Transport for London desires. The constraints that must be addressed and mitigated are not signalling shortcomings, but the myriad of flat junctions that have to be negotiated on every journey, the semi-fast trains that intermingle with all-stations stoppers, and the shortage of platform capacity at the central London termini.

The principles outlined by Geoff are laudable and good, but a large measure of realism needs to be applied to the plans before they are presented to the new Mayor as ‘bankable capacity’.