Rail workers at three train operators are staging fresh strikes on Monday in disputes over the role of guards and driver-only trains which will disrupt travel as people return to work after the holidays and schools reopen.
Members of the Rail, Maritime and Transport union (RMT) at Southern, Merseyrail and Arriva Rail North will walk out amid worsening industrial relations in the industry.
The Southern dispute started more than 16 months ago, with the RMT taking over 30 days of strike action.
The threat of industrial action against the industry's newest franchise holder is also looming.
RMT members on South Western Railway are to be balloted for strikes, just days after the operator took over the running of services from London Waterloo.
Southern said it planned to run most services despite the strike, although there will be a number of cancellations.
The number of Merseyrail and Arriva Rail North trains will be reduced. Services at both companies will run mainly between 7am and 7pm.
Mick Cash, general secretary of the RMT, said: "These strikes are about putting passenger safety before private profit and those that seek to undermine the safety culture on our railways in order to fill their own pockets should be called to account and forced back to the negotiating table."
Paul Plummer, chief executive of the Rail Delivery Group, which represents train companies and Network Rail said: "Britain's railway connects communities across the country and train companies are doing all they can to keep passengers moving on the day many students return to school or college, and people are going back to work.
"Rail companies are working hard to upgrade the railway to support passengers and our economy now and for the long term, including 6,400 more services a week by 2021."