Seltrac Station Skip

[Deleted]

Will the station starters at PED-equipped stations on the Jubilee Line be fitted with full overlaps to allow trains to skip stations at full linespeed? Or will trains still be forced down to a low speed like on the Central?

[mandgc]

Low Non Stop Speed through Tube Stations.

I always thought the low speed restriction for non-stopping trains was due to the restricted clearance between the train and the platform edge.

[Deleted]

Whereas I always thought it was due to the short overlaps on the station starters, necessitated by the fixed block signalling and the desire to allow trains to approach platforms as closely as possible.

[mandgc]

The Northern Line WTT for 1970 says:

"Through Stations-
Mornington Crescent, Passing through station- Both, 20 mph.
All Stations, Euston to Morden - All trains must stop*
*Except where booked,- - authorised,- - emergency,- - -must be reduced to 5 mph at Starting signal after which the train may be accelerated in the normal manner"

I think I am getting into deep water here and will leave it to you to consider the significance of this ! :-)

[tubeprune]

theonekea said:

Whereas I always thought it was due to the short overlaps on the station starters, necessitated by the fixed block signalling and the desire to allow trains to approach platforms as closely as possible.

This is correct. If you shorten the overlap on the starting signal, the home signal will clear more quickly than with a full speed overlap. The 5mph rule was to ensure that a train which overran a starter would not hit the train in front. Of course, it relies on the driver doing the right thing and following the rule.

About 20 years ago, (please someone, tell us exactly when) it was decided to eliminate the risk of a driver not following the rule and resignalled areas had approach control put on the starters. Nowadays, IIRC, the standard says starters are supposed to have 35km/h overlaps - as a sort of "compromise" between the old system and a full speed overlap.

[happybunny]

On the Central Line- outside stations the trains steel creep through at 5mph, however one would imagine the complex signalling system would realise that the train before is 5 minutes down the lane for example, and realise that there is loads and loads of stopping room and be able to not have to slow down so much. I can understand it in the pipe because of the draft, dust etc. But not outside

[Deleted]

The difference is that the Central Line is essentially a fixed block signalling system with ATO grafted on. Because it has fixed track circuit block signalling, the overlaps on the station starters were configured in the same way that every single track circuit block overlap on most station starters on traditionally signalled lines were configured. That's why the Central Line trains can only skip stations at 5mph.

The question I'm asking is whether or not the PED-equipped stations will have station starters with short overlaps. I'm explicitly limiting myself to the PED-equipped stations because the PEDs completely separate the track from the platform, and when a train is skipping a closed station that may have staff or maintenance personnel on the platform, the PEDs will protect them from a train passing through at linespeed.

This discussion needs more BAET...

[happybunny]

Ahhh I see. I really hope so, it would be fun. What about outside stations, ie when going empty from STASG to NEAD when the ATO is in place and fully operational, will trains still pass the stn starter at 5mph?

[Deleted]

Outside stations would probably have 3/4 overlaps, and I would be shocked if trains skipped the station any faster than 25mph. The same would go for the non-PED-equipped deep level stations.