GLASGOW will need a third major railway station in the city centre in less than 20 years to accommodate extra-long HS2 trains unless Carstairs junction is overhauled.

The warning came in Network Rail's completed Scotland Route Study, a masterplan outlining the challenges facing the nation's rail network as far ahead as 2043.

From 2033, the length of the UK's new high-speed trains are expected to double from 200 to 400 metres, making them too long for existing platforms at Glasgow Central - where the HS2 services are scheduled to terminate in the west of Scotland - or for nearby Queen Street station.

Expanding Glasgow Central High Level to either extend or create new platforms "may require the demolition of a number of adjoining buildings", so planners have been urged to consider options including "a new Glasgow City centre station".

Edinburgh Waverley, the terminus for HS2 trains in the east of Scotland, should also undergo "significant and large-scale" redevelopment, including the relocation of retail and passenger facilities away from the main concourse to a new mezzanine level in order to free up concourse space for new and longer train platforms.

Although there are currently no plans to extend the HS2 line further north than Manchester and Leeds, HS2 trains would travel onward to Scotland via the West Coast Main Line.

However, the Route Study warns that the service will run into problems from 2033, when longer HS2 trains are due to be rolled out.

It is proposed that the extended trains will split at Carstairs Junction so that one half can continue to Glasgow Central while the other half heads separately to Edinburgh Waverley.

Both halves would join up again at Carstairs for the southbound leg back to London.

However, the report states: "If splitting and joining does not take place at Carstairs, or any other location, then Edinburgh Waverley and Glasgow Central would have to accommodate 400m long trains.

"There would be a significant impact on capacity for both stations and would necessitate major investment, with consideration of options including a new station in Glasgow and the implications for redevelopment of Edinburgh Waverley."

It adds that the "junction layout [at Carstairs] cannot currently facilitate these activities" and that plans to re-model the junction are focused on improving linespeed and cutting the journey times for existing WCML passenger services - these will "not enable HS2 services to split and join at this location on a routine basis".

However, it adds that the necessary upgrades "could be provided at a future phase".

Even without HS2, the predicted growth in rail travel over the next 30 years looks set to pile pressure on Scotland's railway.

Network Rail forecasts that the number of people using morning commuter services alone could grow more than three-fold in Aberdeen by 2043, with demand for rush-hour trains in Edinburgh and Glasgow more than doubling.

Other possible interventions include building the so-called 'Almond Chord' to link the Edinburgh-Glasgow and Fife lines, boosting the number of passenger services able to run to and from the capital.

Electrification of the East Kilbride and Barrhead lines and from Edinburgh to Perth and Dundee would also pave the way for longer, faster trains to cope with future passenger demand.

Phil Verster, Network Rail managing director for Scotland, said: “The Scotland Route Study provides clear options for the future of Scotland’s railway – setting out key choices for our funders to enable the country to continue to build on the industry’s current success.”