upsidedown's TT bike

I think the actual regulation is relating to drive mechanisms is ARTICLE 1.3.025:

“Freewheels, multiple gears and brakes are not permitted for use on the track during
competition or training. Disc brakes are allowed in cyclo-cross training and
competition.
For races on the road and cyclo-cross, the use of fixed sprocket is forbidden: a
braking system that acts on both wheels is required.”