A railway operator has apologised to passengers who have suffered overcrowded trains in recent weeks.
Arriva Trains Wales (ATW) hopes the situation will improve in the next few days when two damaged trains return to service.
Passengers have been quick to criticise ATW for the situation on social media websites.
Gwen Watson said on Twitter: “Its always the same. Two carriages for a busy train that is often late. And we pay higher and higher fares.”
But the letter, published on the ATW website and on social media, points out some of the incidents that caused significant delays to services on the busy Holyhead to Cardiff via Shrewsbury route were beyond their control.
Lynne Milligan, Customer Services Director, said: “A number of unrelated incidents have meant we have been unable to deliver all our fleet at the right time and in the right place.
“Some of these issues have been caused by freight trains breaking down on our Cardiff to Manchester/Holyhead routes and this extensive disruption led to us needing to re-start services with another train to avoid them being completely cancelled.
“The only way we can do this is by taking capacity from other services, which then reduces the overall number of carriages allocated to each service.
“In addition we have been unable to deliver all our trains to passenger services due to a combination of urgent maintenance or repairs to our fleet.
“Two of our Class 175 trains have been out of service for a number of weeks, one due to striking a tree on the line, but both these trains will be back in service from November 3 greatly assisting capacity and comfort on longer distance journeys.
“We have also had several services affected by low rail adhesion, which is caused by the leaf fall season when leaves are crushed onto the railhead making them slippery.
“This can cause the train to slide along the rails when the brakes are applied and result in damage to the wheels.
“We then carry out the repairs as quickly as possible by “turning” the wheels on a lathe to get the train back into service, but in the meantime this will mean some services run with fewer carriages than normal.”
Network Rail operate a special train to clear the tracks of leaves daily on the North Wales coast line.
A Network Rail spokesman said: “Autumn is traditionally a difficult time to operate in, but we continue to keep the railway running safely and generally very reliably. We do this through dedicated teams who work around the clock to keep the rails clear of slippery leaf mulch.
“We use a fleet of rail-head treatment trains to clean the rails using water jets.
“We work closely with freight operators so when a freight train does break down we can clear the line as quickly and safely as possible.”
