The Class 320 units are fitted with GSM-R cab radios and took part in the GSM-R trial in the Strathclyde area. Their interior design includes paintings of various landmarks and famous sights along the various SPT rail routes on the car ends. This meant that the units could be used on the sections of the Argyle Line route shared with the West Coast Main Line (and in theory, the Airdrie-Bathgate extension of the North Clyde Line and beyond, although this is currently prevented by a lack of DOO equipment) and also allows full-speed running in multiple with the near similar Class 318. However, yaw dampers were fitted across the class in 2010, allowing them to run at 90 mph (145 km/h). The lower design speed meant that yaw dampers could be omitted from the class.

With much shorter passenger journeys in mind, the Class 320 units originally lacked the toilets of the Class 321 units and also began life with a lower speed capability (75 mph or 121 km/h) due to the much closer spacing of stations on the North Clyde Line. The units run on 25 kV AC overhead line supply via a Brecknell Willis high speed pantograph, using four Brush TM2141B traction motors. The trains were built against lot numbers 31060–2, which were issued on 6 January 1989 and completed on 31 October 1990. Built in 1990 by British Rail Engineering Limited's Holgate Road carriage works, 22 three-car sets were ordered by SPT to replace the Class 303 and Class 311, which were by then 30 years old. The Class 320 is effectively a three-car derivative of the Class 321 units found in and around London, East Anglia and Yorkshire.

The v320 overhead