The InterCity 125 was planned as a stop gap measure, meant to fill until electrification was spread across all main lines and the Advanced Passenger Train (APT) was in service. Research had begun for the tilting train but it was not possible to predict when the APT would enter service. 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 was still in widespread use in .