The following is reproduced from a BR Educational Service card titled "Discovering Railways Advanced Passenger Train (APT)".
The Advanced Passenger Train is not only the fastest train on British Railways — capable of speeds over 250 km/h (150 mph) — It also leads the world in showing completely new ways in which high speed rail travel can develop.
Very fast trains usually depend on the costly laying of new track to get rid of severe curves. The APT does not need this, thanks to a new self-steering system for the wheels which enable the train to go round curves much faster than ordinary trains. The coaches also tilt inwards on curves, like an aircraft very gently 'banking', to make it more comfortable for passengers.
The introduction of APT's into the longer Inter-City routes will mean quite dramatic shortening of journey times. This will give cars and even aircraft some severe competition.