The Class 170 is a Diesel Multiple Unit built by Bombardier between 1998 and 2005. A total of 122, two or three carriage units were built in this time.

The units have a top speed of 100mph, powered by their MTU 6R 183TD13H engines, found under the floor of each 23m long carriage. The units can be found in many locations across the United Kingdom, including Scotland, the Midlands, the South, and the South East.

ScotRail operate a total of fifty-five Class 170 units, the most of any operator. The ScotRail fleet consists of the Class 170/3, and Class 170/4 subclass, with all units being in a three car formation.