I've just driven 9Z23, one of the LGV specials in SEHS (starts at 13:10 or so?) As it comes into Stratford, TVM gives an expected reduction in speed, from 230 km/h line speed down to 200 km/h, then to 170 km/h at the last but one signal flag before Stratford. The last signal flag in the tunnel before Stratford then gives a 000 (stop) requirement, with just over 1000 yds to go until the next signal. Even at full emergency braking the TGV can't make that stop. The signal then clears again just before you get to it and sets you back to 170 km/h, but this is then repeated at the next signal.
