Jerky trains

At slow speeds, such as approaching West Hampstead southbound when held up by a preceding train, it's the atrocious TBTC software incapable of low speed control - goes to max then brake repeatedly, compounded by the siding pointwork (though better since they renewed it).

I'm only aware of two jerky starts - southbound from West Hampstead where recent track renewal seems to have produced a conductor rail gap or a control glitch: and southbound out of Baker Street over the sharp curve off the link to the Bakerloo line.

There are various reasons for this, ATO trains seem to be covered above, but it can also occur because of rail gaps causing motors to drop out as trains accelerate.  Northwood on the south is particularly noticeable for this as trains cross the points which access the siding.

jamesb , What you describe is a combination of motors cutting out as they pass over gaps in the conductor rails crossing pointwork and the tendency for trailer cars to jolt around slightly when this happens. The sharper rates of acceleration on ATO lines certainly exasperates this mini ping pong effect.

The same goes for the S stock which has fully motorised cars although it's nowhere near as bad as the 1996 and 1995 stocks. One of the worst examples of this is the Southbound run of the Northern line from Moorgate, the train launches forward before coasting abruptly for the 15mph speed limit just after leaving the station. Another cause I have found that is amplified with ATO when on the 95 and 96 stocks in particular is when the brakes don't fully release as the train motors up, the slightest delay can cause a proper jolt. I generally think that the responsiveness of the 1995 and 1996 stocks with the ATO system that now drives them is a poor match.

As well as the gaps and closely following of trains mentioned above, another cause for jerky movement when leaving stations can be attributed to a temporary loss of pilot light ("door closed visual") in turn causing the motors to drop out when they were applying full power. Maybe someone is trying to remove a trapped coat or bag strap causing the temporary loss.

So much for smooth rides which LUL used to demand; I remember an instructor once told me that he used to tell his trainees he did not want them to spill his tea whilst stopping or accelerating! With ATO that seems to have gone out of the window.