SCOTRAIL is so short of trains following the opening of the Borders Railway that it may be forced to hire extra carriages to cope with booming demand across the network.
Travellers on the line have complained of overcrowding – as have commuters on routes across the Central Belt.
Other packed services include the North Berwick and Dunblane lines into Edinburgh, and the Ayr-Glasgow route.
Dutch firm Abellio, which took over ScotRail in April, has ordered nearly 100 new trains but the first will not arrive for another two years.
It has already been forced to hire two old-fashioned locomotive-hauled trains to replace four shorter trains transferred to another operator in England after their leases expired.
The operator has increased the size of most weekend trains on the Borders line from two to three or four carriages because of “huge demand”.
Two weekday rush-hour services have also been given additional carriages, but these have had to come from elsewhere in Scotland.
The train shortage is chronic, with previous ScotRail operator FirstGroup being fined nearly £70,000 after a Dunblane to Edinburgh commuter train ran with too few coaches more than 120 times between 2012 and last year.
The ScotRail Alliance, which includes track owner Network Rail, admitted it may struggle to meet passenger demand, which has increased by one third over the last decade.
Managing director Phil Verster said: “Our challenge in the next two years, till we get the new fleets in place, is to firstly move our existing rolling stock around the network and to utilise that as best we can.
“Then, if that still does not meet the overall demand that we see, we will consider whether we need to lease further trains.”
Verster said the new train fleets would make a “huge impact” on crowding, increasing total seats by 30 per cent as well as cutting journey times with their faster acceleration.
He also said the platform at North Berwick station would be extended to accommodate longer trains.
Some 91 million journeys a year are made on ScotRail, which is thought to be a record despite the network being far smaller than before large-scale route closures in the 1960s. ScotRail wants to increase that number to 139 million over the next ten years.
Mid Scotland and Fife Labour MSP Dr Richard Simpson said: “Extra carriages announced for Borders rail is great for Borderers, but overcrowding on the Alloa and Dunblane to Edinburgh lines continues unabated.
“These are all when there are the supposedly ‘correct’ number of carriages.”
Retired pilot Ian Somner from Edinburgh said there was “severe overcrowding” on rush-hour trains on the line, while fellow commuter Leo McCann claimed the 5.14pm Edinburgh-North Berwick weekday service was “dangerously overcrowded”.
Watchdog Transport Focus said that passengers would not wait for the new train fleets to arrive for improvements.
Transport Focus passenger manager Robert Samson added: “Passengers in Scotland have long said that their trains are too crowded.”