The Carstairs–Edinburgh line was electrified in 1991 as part of the electrification of the East Coast Main Line (ECML). When this was completed, two new services from Edinburgh to Glasgow via Carstairs were reintroduced. Although the line via Carstairs is the longest of the various routes between Edinburgh and Glasgow, its electrification allowed the London King's Cross to Glasgow Intercity services (which had previously run to Glasgow Queen Street via the E&GR line) to be operated by InterCity 225 electric trains and diverted to Glasgow Central station. Electrification of the Queen Street route was not planned at the time, and the London services caused congestion at Queen Street where the platforms were not long enough to accommodate them. 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. Some of these services operate all the way through from Glasgow Central to North Berwick.