Edinburgh To Glasgow line: Future trains?

[NotATrainspott]

Why is it the trains from London to Glasgow via Edinburgh on the ECML take the longest possible route to Glasgow via the crazy circuitous route via Carstairs?

There are four-and-a-half different lines from Edinburgh to Glasgow. One-and-a-half (the E&G plus the loop via Cumbernauld, and in future also the loop via the Dalmeny Chord) run only into Queen Street HL. While in the past there have been a few InterCity services to England from Queen Street they were rare because of platform length issues. The E&G is also the fastest line available but there is really no space and no real need for InterCity services to share the route. Another one, the most physically direct one, is the Airdrie-Bathgate line which was only reopened in 2011 and acts purely as an extension of the North Clyde electrics service, so cannot possibly be used for InterCity routes.

The remaining two lines head into Glasgow Central, which is the right one for InterCity services to England. The route via Carstairs may be longer but it is the main InterCity route for WCML services heading to Edinburgh; therefore it was electrified first while the secondary Shotts route has until now mostly been left alone. Upgrading the Shotts line for just the fast InterCity services from Edinburgh to Glasgow, when it serves many more suburban and rural locations, wasn't a particularly good idea when there was an existing fast InterCity line that really wasn't that much longer in the grand scheme of things. End-to-end Shotts line timings are comparable to Carstairs timings.

There is a concept of building a new Glasgow to Edinburgh high speed line, which would form part of the future HS2 infrastructure in Scotland. No real details have been discussed about this line but one of the things that must be optimised is how far south and how tight the delta junction (Glasgow/Edinburgh/Carlisle) would be. I think it would be further north than Carstairs, because the E&G services would be limited to 230km/h and the extra distance travelled by London/Birmingham services would be irrelevant at >330km/h over hundreds of kilometres.

 

[jopsuk]

They need to go to Glasgow Central (because of the platform length required), and there's only one electrified line from Waverley to Glasgow Central, and that is via Carstairs. I believe even after electrification of the Shotts line, the line speed makes up for the extra distance it has to travel (and it avoids scheduling it around stopping trains for much of its route).

Also provides a direct service for Motherwell- the XC services also go this way