Rail passengers going from Bromsgrove to Birmingham this week face using a replacement bus service due to a trains shortage and a busy Easter break.
Signage at the station was warning people certain services were already very busy before they arrive there and alternative transport may be needed.
Operators London Midland said the firm could not just put more trains on.
It said there "aren't enough diesel trains left in the country to meet the demand that we're seeing".
Spokesman Francis Thomas added: "So rather than leave people stranded we felt this was the right thing to do.
"The good news next year is the line to Bromsgrove gets electrified and three extra trains an hour will run on that route."
Sarah Wooledge tried to get on a train on Wednesday, but had to get a bus and missed her connection to London.
She said: "Unfortunately we were told that the train was full from Hereford and they had lots of problems and couldn't fit us on.
"So we had to get a bus to Longbridge and then from Longbridge a train up into New Street."