Based on the Class 317 design, this fleet of 21 3-car sets for Glasgow area operation were launched from 1985. The units are gangwayed throughout and have all power and control equipment, including the pantograph on the middle vehicle. Since introduction the sets have mainly been used on Clyde area services, but from 2002 sets should start to appear on North Berwick line services as part of the cascade of stock caused by the introduction of Class 334s.
When introduced the 318s were finished in Strathclyde orange livery, this later gave ay to Strathclyde maroon and cream.