Extra carriages are being added to some Borders Railway services following a flurry of complaints from passengers in Tweedbank and Galashiels about overcrowding.
A number of ScotRail customers have complained the two-carriage provision on the line over the past week.
ScotRail said it had tried to allow for the “novelty factor” of the Edinburgh to Tweedbank route but the level of interest had been “remarkable”.
It said it was looking at doubling carriage numbers at some times.
Passengers posting on social media have been complaining about overcrowding, with some unable to board some services at all. Others have complained about a lack of car parking spaces and long queues to buy tickets at Tweedbank.
Scotrail said demand on the line has been considerable since it opened on September 6 and that it is working on solving the problems.
A spokeswoman said: “We are continuing to monitor passenger numbers so we can tailor how to make best use of the carriages available to us.
“For example, we may have found a way to temporarily double the number of carriages on a Sunday, and aim to do the same on Saturdays during peak times.
“We are also planning to add carriages in the short term to one particularly busy service, the 16:24 from Edinburgh - Tweedbank which is key for commuters.”
The Campaign for Borders Rail said it had repeatedly warned that there would be “much more demand than was being planned for”.
“We are delighted that the Borders Railway is already proving sceptics wrong, and that is to be celebrated,” a spokesman said.
“However, we raised the issues of underestimating demand with the Scottish government and its Transport Scotland agency in advance of the opening and even before track laying commenced.”
Rail consultant and author David Spaven said: “The level of interest in travelling on the railway wasn’t at all ‘remarkable’ – it was highly predictable, and ScotRail were warned by campaigners, but chose to ignore well-informed advice.
“Poor management by ScotRail has led to a pretty shoddy experience for too many travellers who are new to rail. It was critical to get things right in the first few weeks of the railway, but the opportunity to build on all the goodwill towards the new railway has been partly squandered.”