The Carstairs to Glasgow section was electrified by British Rail in 1974 as part of the electrification of the Weaver Junction to Glasgow Central section of the WCML. The Carstairs to Edinburgh section was not electrified at that time. Many long distance trains from the south used to split into separate Edinburgh and Glasgow portions at Carstairs, and diesel locomotives continued to operate the Carstairs to Edinburgh part of the service. This procedure added significantly to journey times, typically adding at least 20 minutes to Edinburgh schedules. Division on northbound services was relatively simple, with the electric locomotive continuing forward with the Glasgow portion of the train, while a diesel loco would be attached to the rear part and would haul the Edinburgh train in the opposite direction. However, attachment would involve the section from Edinburgh arriving into Carstairs first behind a diesel locomotive, and pointing in the Glasgow direction, with the Glasgow portion running past under electric power. The Edinburgh portion would then reverse back into the opposite platform to join the back of the Glasgow section and the fully joined up train would then head south. After WCML electrification the Edinburgh trains were typically hauled by a Haymarket locomotive fitted with Electric Train Heating, either a Class 47 or Class 40.