Thousands of commuters face three days of travel chaos across Scotland from tomorrow as last-ditch efforts to avert rail-strike action failed last night.

Fewer than 30% of local and cross-border services are expected to be running during the two-day stoppage with unions raising concerns for the safety of passengers with those trains that will remain running.

More than 400 signal workers, who are responsible for ensuring trains run safely, are expected to walk out for 48 hours from noon on Wednesday in a dispute over the number of rest days provided for staff undertaking new work rosters.

Network Rail, which owns and operates the rail infrastructure, was accused by the Rail Maritime and Transport union of bringing in managers from England with insufficient training or understanding of Scotland to man signal boxes to keep some services running. The RMT has reported Network Rail to the Railway Inspectorate, the independent economic and safety regulator.

Network Rail denies that unqualified staff will man signal boxes. "They absolutely understand Scotland," said a spokeswoman. "They are not allowed to work on a signal box unless they have passed tests on that route."

The dispute hinges on the refusal by managers at Network Rail, which owns and operates the rail infrastructure, to agree to provide an extra rest day during a 12-week shift cycle in return for effectively retaining a 36-hour working week instead of reducing it to 35 as was agreed through pay bargaining. Both sides failed to reach any agreement over rest days at the end of a three-hour meeting yesterday.

David Simpson, Network Rail's route director, Scotland said: "We are hugely disappointed that the RMT is going ahead with this strike without fully exploring all negotiation opportunities."

Mary Dickson, First ScotRail's managing director, said: "We are providing as many services and as robust a timetable as possible in difficult circumstances."

The Automobile Association said commuters should plan ahead and ensure they talk to employers at an early stage to reach an agreement on how to handle working on the days in question.