 The HST applied what had been learned so far to traditional technology – a parallel project to the APT development, based on conventional principles but incorporating the newly discovered knowledge of wheel/rail interaction and suspension design.The class holds the world record for diesel traction, achieving 148.4 mph (238 km/h) with a shortened set running speed trials between Darlington and York.Unlike the APT, the InterCity 125 was an outstanding success and is still in widespread use in .