You may be thinking of the Shinkansen gauge. I understand their conventional lines to have a maximum height of 4100mm which is close to 13ft 6in and very near typical UK dimensions.Not on the similar Thunderbirds. Don't forget they have a much larger loading gauge than us- (14ft 8 maximum height) so there is plenty of height to play with.
A Japanese diagram:
https://ja.m.wikipedia.org/wiki/車両限界#/media/ファイル:Rolling-Stock-Gauge-in-Japan.svg
Blue: older NG lines
Grey: newer NG lines
Green: Shinkansen