The units were originally intended to operate on the Argyle Line but, mainly because the platform monitors on the Argyle Line stations did not line up with the driver cabs, the units were initially restricted to the North Clyde Line, although they were occasionally used for VIP trips from the high-level platforms of Glasgow Central when they were the newest EMU stock in the SPT fleet. The problem was resolved in 2011 and the units began entering service to replace the final Class 334 units on the Argyle Line. From December 2016, Class 320s started to operate on the Cathcart/Newton lines from Glasgow Central High Level to replace a number of Class 314 units that were transferred to the Inverclyde Line.