SCOTRAIL has apologised for overcrowding on its flagship Edinburgh-Glasgow service, blaming mechanical failures and two crashes elsewhere on the rail network for a shortage of train carriages over the past three weeks.

The operator said it was now planning to spend more than £200,000 hiring an additional train to ease the problems, which have seen thousands of passengers struggle to get a seat on Scotland's busiest rail route during the morning and evening rush hours.

It comes after The Herald revealed in July more than 2600 trains a year were classed as not having enough carriages to meet demand – known as "shortforming" – in 2010 and 2011, an increase of more than 60% in five years.

Trains are normally doubled in length, typically from three to six carriages, to cope with a surge in journeys by city-based commuters during peak periods.

However, an increase in the number of services on the network and a shortage of maintenance facilities to ensure faulty trains are repaired promptly have been blamed for putting a strain on the size of the available ScotRail fleet.

The latest problems have been exacerbated by a crash between a ScotRail service and 4x4 at a level crossing at Dunragit village near Stranraer on October 7 which left Andrew Robertson, the 18-year-old driver of the vehicle, with serious injuries.

A second incident involved the 5.56am train from Dundee to Glasgow on October 17 which struck and killed a man at the Cornton level crossing, north of Stirling. Police said there were no suspicious circumstances. The two incidents left ScotRail with three out-of-service train carriages, a spokesman for the company said. It is planning to introduce an additional train on the Fife circle within the next 10 days, which will free up an additional two trains to operate on the Glasgow to Edinburgh via Falkirk line.

"We apologise for having to run fewer carriages on some services on the Edinburgh- Glasgow route in recent weeks, resulting in a less comfortable journey for our customers," the spokesman said.

"We can assure customers we are working hard to resolve these issues as quickly as possible – and using every train at our disposal. We have already made arrangements to hire an additional train, at a cost of more than £200,000, to operate on the Fife Circle this winter. Its introduction – within the next 10 days – will free up two trains to alleviate issues on the Edinburgh-Glasgow line."

There are currently only two maintenance depots with pits that can deal with the majority of issues affecting the 155 diesel trains that operate between Glasgow and Edinburgh. Discussions have taken place about building an additional depot, but the plans have not been approved by the Scottish Government.