Guards on Southern trains have walked out on strike for the 29th time in their long-running row over safety.
Talks between the Rail Maritime and Transport Workers union (RMT) and Southern broke down last week in the 10-month-long dispute.
It centres on Southern’s plan to make conductors on-board supervisors, giving drivers control of carriage doors.
Southern said it expects to run “around three-quarters of its normal service”, despite the industrial action.
The rest will either be cut completely, be replaced by bus services, or run with fewer carriages than normal.
Angie Doll, passenger services director at Southern said: “We will be running as many trains as possible on Wednesday but our advice to passengers is to expect some disruption and check on our website before you travel.”
The 24-hour strike, which began at 00:01 GMT, comes after ongoing talks ended on 14 February without deal.
‘Lines of communication open’
Two days later, members of train drivers’ union Aslef voted against a deal union leaders had agreed with Southern.
A fresh set of talks with the rail firm got under way, earlier.
An Aslef spokesman said it was re-opening of negotiations at the earliest opportunity since the ballot result, but given the length of previous debates, a quick resolution was not expected.
Southern’s parent firm Govia Thameslink (GTR) added: “All we can say is that lines of communication are open.”