The new generation Class 170 multiple units were built at Derby and feature a welded aluminium body structure and hydraulic transmission. Each vehicle is powered by a 422 Horsepower diesel engine providing a maximum unit speed of 100MPH. There are no un-powered trailer vehicles.

The engine and transmission are situated under the body and provide drive to one bogie per vehicle. Class 170 units use a BSI automatic coupling to work in multiple and are also compatible with British Rail classes 150, 156 and 158 Sprinters.

Class 170 units have been categorised into six sub-classes all with the same basic specifications - the differences are seating arrangements specified by the different operators. This can vary the unit weights by up to 2 tonnes.