In message . com,
Boltar writes

I've noticed the victoria line seems to be much warmer than the other
lines these days (or maybe it always has been but I've not noticed).
Is this because the trains are more frequent , or they use up more
energy on ATO , or the tunnel ventilation isn't so good , or is there
some other reason?

Perhaps its because Victoria-line trains remain entirely underground
while in service.
--
Paul Terry