The 23 metre, 90 mph ultimate development of the “Sprinter” concept produced by British Rail workshops from 1989 to 1992. Constructed in Aluminium and fitted with the Cummins 350 hp NTA 855 engine driving a Voith transmission these units are built for regional railways long distance services. They are able to work in multiple with class 14X, 15X and 17X Turbostar, and provide a superior ride thanks to their P4 and T4 bogies, known as “series 4”. Doors are at the vehicle ends, allowing flexible layout of the interior and helping provide an “inter-city” ambience. Couplers are the Regional Railways standard BSI and gangways are compatible with the class 150/2, 153, 155 and 156 units, although the inner end gangways are wider so an adaptor plate is needed if different formations are required. The majority of units are formed as two-car sets, with 17 x 3-car sets also part of the fleet. Small twin- leaf doors are fitted