| Topic: | Re: Mike Brown's Longing for a Piccadilly Line Stop at Turnham Green | |
| Posted by: | Richard Jennings | |
| Date/Time: | 15/02/20 19:21:00 |
| Let me try to inject some facts into this discussion. The signalling 'blocks' referred to in recent posts basically correspond to the signals that are placed by the tracks at intervals. For example, on the eastbound Piccadilly at Turnham Green, a green signal at the east end of the platform gives the driver permission to proceed as far as the next signal which is just short of Stamford Brook station. Between TG and Hammersmith there are about 9 signals (not counting repeaters), with the signals much closer together as you approach Hammersmith because that minimises any delay caused by a train ahead that is just departing the platform there. The problem with Turnham Green is that the signalling was not designed to handle stopping trains at the full line frequency of 21 to 24 trains per hour (tph). It could only handle 24 tph if every single train was on time to the second, and only stopped for 20 seconds, not a situation that is realistic. If you want to run a service at 24 tph (1 train every 2.5 minutes) you need signalling that will cope with a train every 1.5 minutes, otherwise you can't recover from any slight deviation from the timetable. In the tunnels through central London, the signalling does have that capability, but not at Turnham Green. That means that Turnham Green would in practice become a bottleneck if all trains stopped there under the current signalling. Any slight delay would be made worse, and the reliability of the service would suffer for all Piccadilly passengers. There has also been reference in this thread to trains crawling slowly through Turnham Green. That will only happen if there is congestion on the line. In my experience some years ago that mainly happened on the westbound when drivers are being changed at Acton Town. Although allowance is made in the timetable for this, it often didn't seem sufficient. I haven't seen eastbound crawlers like that, but I'm not usually there in the morning peak. |