A similar option for HS2?
250kph Intercity express trains are super-expensive
We have museums full of old steam trains
We fit big resistive electrical heaters in the boilers, run form overhead power lines
= cheap high speed locomotives ready in days
Then we decide we can't electrify the entire line and we've run out of old steam locomotives and we need to make it carbon neutral so we invent miniature nuclear reactors to generate the power to run the heaters to make the steam (we then abandon our design and buy the reactors from N. Korea)
Then we decide it's too dangerous to put the reactors on the train.
So we position them every 10miles along the track, the loco connects to power, raises steam, and runs for 10miles until the boiler is cold
Announce massive success in investing billions in clean power, high speed rail and bringing jobs to run down steam locomotive building regions