Do drivers have this choice for the moment on the SSR? I remember reading somewhere that on the Central Line, driving trains in coded manual tended to delay the service because even the best manual drivers just weren't as good as the computers at keeping up with the signalling system's target speeds.
I guess this may not be an issue on the SSR for a while, until they do the speed and capacity uplift.
On paper, no. The expectation is that it’s primarily an ATO system and that is the normal mode of use, unless there’s an operational reason not to. There may be an exemption during the early days in order to allow drivers to practice if they so wish.
However, in the real world, providing drivers can maintain time, and not have any form of incident (*) that wouldn’t have happened in ATO, no one really minds. Good drivers can quite easily maintain Thales ATO performance, and very good ones can actually very slightly surpass it. On the Central it’s also possible to keep up with it, albeit this requires driving very hard, and one has to consider there’s the risk of having a SPAD on the Central Line.
(* Seltrac has an unfortunate design flaw that the train can lose communication with the system if the train experiences wheelslide, which can happen if the driver inadvertently has an over speed and the system intervenes to emergency brake the train. This will then cause a delay as the train has to be re-entered into the system. On the Jubilee and Northern this can take up to 10-15 minutes, although I believe on SSR it’s a bit quicker, a benefit of the radio system over the inductive loop cables. It’s this design flaw which is the main reason we see a pathetically low brake rate in the open sections, and this applies in ATO too. I’m not sure if SSR has bettered this, it’s still very much an issue in the Jubilee and Northern, despite a lot of work it seems that the low brake rate in the open is here to stay, with any attempt to uplift it pretty much abandoned. )