Trains: Frustration over Carmarthen-Milford Haven rail cancellations
Train passengers in west Wales say they feel their service is being treated as "dispensable" after a 40-mile section of line was closed for five weeks.
A replacement bus service is running between Carmarthen and Milford Haven until 22 December as Network Rail clears vegetation alongside the tracks.
Rail campaigners and businesses have said it is causing major disruption.
In a joint statement, Network Rail and Transport for Wales (TfW) said the work was "essential" for passenger safety.
The bus journey between Carmarthen and Milford Haven can take up to two hours and some businesses say they are losing valuable time and money working around the delays.
"We've got a client in Dale who needs 24-hour care," said a manager at a Pembroke Dock care agency.
"We're having to pick the carers up and take them to the replacement bus service and then take the replacement carer back - it means that we're out of the office for three-and-a-half hours at a time.
"It's frustrating, there's work we should be doing but we're doing this instead."
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Network Rail explained the work includes clearing dying and diseased trees after a train hit a tree on the track in the Fishguard area in October.
No-one was injured, but the line was closed for more than a week.
Erene Grieve of the Pembrokeshire Rail Travellers' Association said some passengers had arrived at the station in the morning and "there was no train".
"People have been terribly affected and the thought that it's going on for five weeks - it just trails on.
"I don't know whether closing the whole line was absolutely necessary. It could have been staggered more. They seem to do that on this line - as though it was dispensable."
Network Rail and TfW said they were working together to keep disruption to a minimum and were advising passengers to check before travelling.
"We are pleased to be carrying out this essential work on the Milford Haven line to improve the safety for passengers, the public and our staff," said Bill Kelly of Network Rail.
"We would like to thank passengers and line-side neighbours for bearing with us as we carry out this essential upgrade work."
TfW insisted it had publicised the cancellation of services well ahead of the line closure on 18 November.