YORK train operator Northern says it again expects to run only about 30 per cent of services on Saturday because of another strike by members of the RMT union in a long-running dispute over guards.

It said it was advising customers to plan carefully if they intend to travel on the rail network, with very few services running before 9am or after 6pm.

"On those routes where we are able to operate trains, we expect all services to be extremely busy," said regional director Liam Sumpter. "We will also have replacement bus services available on some routes where trains aren’t running."