In a seven-day period earlier this month, faults with carriages and vandalism saw 25 of the 42 Melbourne-Albury trips replaced with buses.

Only two sets of trains, engines and carriages, are needed for the three daily V/Line services, a third set held in reserve for emergencies.

But the standard maintenance program means the third train is available for just one week each month and now, with one train in for major maintenance, there will be no spare set until at least May.

Rail authorities say buses are the next best option.

A spokeswoman for Public Transport Victoria also blamed the heavy maintenance schedule on the state of the Australian Rail Track Corporation’s mudhole-plagued line.

“Two train sets are required to operate the Albury line’s three return trips a day — which means there is already one spare train set allocated in the current fleet to allow for faults and maintenance works,” she said.

“Since the return of passenger services to the North East, a number of Albury line train services have been replaced by coaches because of excessive wear and tear on the train carriages due to the condition of the ARTC track.

“As the ARTC has continued to fix problems with mudholes in the track, the wear and tear on V/Line locomotives and carriages has significantly reduced.

“Under a maintenance program designed to prevent unexpected faults from occurring, there won’t be a spare train set available until May, which means in the event of vandalism or an unexpected fault, V/Line’s ability to run all timetabled trains can be put at risk.

“Public Transport Victoria and V/Line have considered the possibility of adding a fourth train set to the Albury line to manage this risk but have agreed that the best option is to continue the maintenance regime and have replacement coaches on standby.”

A V/Line spokesman said airconditioning issues, which saw buses used for almost a week, were being remedied.

“These faults related to a safety switch and seal leak,” he said.

“The manufacturer is aware of the problem and has proposed a solution which we are implementing during the major service of the carriages.

“The airconditioning on the Albury line trains, upgraded as part of the standard gauge conversion, has up to this point been the most reliable system running on our N Set fleet.

“When a fault occurs we ... replace the service with airconditioned coaches for passenger comfort.”

Public Transport Victoria says it will work with V/Line to find ways to improve reliability, including examining future fleet requirements