Never particularly thought of it that way Nige; but the telling point is I guess, that cabling / pure electric appears to be the preferred option to Diesel-Elect where available? All before Greta Thunberg etc, so you’d have to assume the accountants are responsible?
Its a measure of just how complex finding viable solutions maybe, everything with a cost to this planet but often not given in general discussion as focus is often on immediate environments.
Just that trip across London for us, district line to nottinghill gate, then hybrid double decker bus (sit up top at the front, as them's the rules
) electric pull away, fuel (possibly lpg) after about 100 mtrs, dont know if it's regen stopping, we crossed, all in one combination, Paddington approach route, you can see tunnel entrance to new Cross rail Elizabeth line, under the high level westway motorway, while simultaneously going over the Grand Union canal coming down into Paddington Basin from industrial supplying areas.
Certainly quite a sweep of all available transit/transport systems, and brings into focus just how long term decisions have to play out in reality. also with every city on the planet having this complexity of infrastructure built or building up.