The Caledonian therefore opened its direct route via Shotts in 1869, and diverted all of its Edinburgh to Glasgow services via that line.

In addition, as the North Berwick Line was included in the ECML electrification and the depot for its EMU trains was Glasgow Shields Road TMD, a limited stop ScotRail service was also introduced between Edinburgh and Glasgow via Carstairs partly as a means of using what would otherwise have been empty stock movements.

From 2011, changes to the franchising arrangements resulted in most of the East Coast London King's Cross to Glasgow Central services being withdrawn.

Starting from Glasgow Central (High Level), the line follows the main spine of the WCML to Motherwell where it continues to Carstairs.

South of the station, the line splits at Carstairs Junction where it joins another branch from the southern section of the WCML through a tight curve with a permanent speed restriction of 20 mph.

It is generally not regarded as a main commuter route between Glasgow and Edinburgh owing to its circuitous route which involves travelling 30 miles south towards Carstairs and returning north again, and the lack of available train paths since long-distance freight and express services are given priority on it.

However, due to engineering work at Edinburgh Waverley from late July until November, only one return service per day used the line.

Virgin Trains West Coast operated services from both Edinburgh and Glasgow Central to London Euston via the WCML.

Virgin CrossCountry operated services from Edinburgh via the ECML and Glasgow via the WCML to destinations as far as Brighton, Bournemouth and Penzance.

The users of the line were: As of May 2018: Abellio ScotRail (ScotRail since April 2022) run a service roughly every two hours between Glasgow and Edinburgh calling at Motherwell, Wishaw, Carluke, Carstairs, Haymarket and Edinburgh Waverley though 2 trains call at Kirknewton, Curriehill, Wester Hales, Kingsknowe and Slateford.

TransPennine Express run hourly from Manchester Airport to either Glasgow Central (1tp2h) or Edinburgh (1tp2h), alternating with Avanti West Coast services.