In the summer of 2001, I used to commute to Richmond in London via Turnham Green on the District Line. I was frustrated that the Picadilly Line trains didn't stop there during the day -- when I really wanted them to. So, to find out why, I asked London Underground Limited.
I had thought that their answer had been lost in the sands of time -- but, as it turns out, it was sitting in my email archive all along. So, for posterity's sake, here it is:
Is there a reason why the Picadilly line doesnt stop at Turnham Green during normal hours?
Dear Mr Wallace
Thank you for your recent email enquiry.
The level of service provided at individual Underground stations is subject to regular review, taking into account substantial changes in demand, be they actual or perceived. Passenger opinion, including responses to origin and destination surveys, forms an essential part of the review process, as does the potential increase in passenger numbers created by expansion of residential or commercial development in the vicinity of stations.
In determining whether additional stops can be justified within an existing route, consideration has to be given to the effect on overall journey times and the availability of resources to maintain required frequencies. Since September 1996 the Piccadilly Line timetable has offered by far the most intensive service anywhere on the London Underground network. Trains are scheduled at two or three minute intervals between Arnos Grove and Acton Town for the greater part of the day, which, due to present constraints in track and signalling system capacity, can only be achieved by running non-stop between Hammersmith and Acton Town, six minutes being allowed in the schedule for this.
During early morning and late night periods, when trains on both the District and Piccadilly Lines run less frequently, Piccadilly Line trains are able to call at Turnham Green, adding one minute to the scheduled journey time between Hammersmith and Acton Town. Between 0645 and 2230 on Mondays to Fridays some three hundred and seventy Piccadilly Line trains in each direction pass through Turnham Green without a scheduled stop. Were all these trains revised to call at Turnham Green, the cumulative effect on the timetable would be an increase in the total running time equivalent to a return journey between Cockfosters and Heathrow. Unless there was a reduction in the existing frequency, two further trains and at least six extra drivers would thus be needed if Turnham Green is to be served by Piccadilly Line trains all day. On the basis of survey results to date, the marginal increase in revenue generated is unlikely to be sufficient to fund these additional resources in the foreseeable future.
Meantime, the District Line daytime service has been enhanced to provide a train about every four to six minutes between Hammersmith, Ravenscourt Park, Stamford Brook and Turnham Green, with Ealing Broadway services linking Turnham Green, Chiswick Park and Acton Town at intervals of eight to thirteen minutes. Cross platform interchange between the Piccadilly and District Lines is available at Barons Court, Hammersmith and Acton Town; since Hammersmith is a busy station in its own right, many passengers prefer to make westbound connections at Barons Court.
In exceptional circumstances, arising perhaps from a signalling or train equipment failure, Piccadilly Line trains may be diverted to run via the District Line tracks. Since there is a need to interlace with District Line trains in so doing, the number of Piccadilly Line trains in service might need to be reduced accordingly. The Line Controllers, in consultation with their District Line colleagues, can arrange for Piccadilly Line trains to call at the intermediate stations between Hammersmith and Acton Town on these occasions, if the disruption is likely to last some time. More commonly, individual Piccadilly Line trains will call at these stations to compensate for prolonged gaps in the District Line service. Piccadilly Line drivers have also been instructed to open the train doors at Turnham Green if the train has stopped in the platform because the signal ahead is displaying a red aspect.
I hope that this is of assistance.
Customer Service Centre
London Underground Limited