Passengers on three train companies across England are seeing action by striking union members on Monday.
Northern rail staff are on the last day of a three-day strike, while Merseyrail staff are on strike for the day and also plan action on 23 July.
RMT union members at Southern have walked out on a one-day strike.
The union is in dispute with the companies over driver-only-operated trains, which it says would be unsafe and lead to widespread job losses.
“The threat to abolish guards and introduce driver-only-operated trains is only part of the wider attack on rail services,” said the RMT.
The union said the dispute is not about pay or conditions but strike action is over “concern about passenger safety”.
In April RMT members demonstrated against the proposals and to mark the one-year anniversary of its dispute with Southern rail.
Northern said it expected to run more than 40% of its timetable and it would have additional rail replacement buses.
Sharon Keith, regional director at Northern, said: “We are doing everything we can to keep our customers on the move during the three days of industrial action affecting our network.”
However, all services are expected to be extremely busy and travellers should allow extra time for their journeys, the company added.
Most services are timetabled to run between 07:00 and 19:00 BST with many routes winding down from late afternoon.
Commuters have been taking to social media to say how their working days are being affected by the strike.
Kitty tweeted: “I was all ready to go this morning. Then I realised there is a #NorthernRail strike. So I get a half an hour lie in!”
Charlotte posted: “Last train home at 5.32 – don’t usually leave the office until 6! #earlyfinish #trainstrike #northernrail”
Merseyrail trains are running from 07:00 to 19:00 but some stations will be closed. There are no trains scheduled to run on the Ellesmere Port, Hunts Cross and Kirkby lines.
Jan Chaudhry-van der Velde, managing director, said customers were urged to check before travelling.
He added: “The team has put together the best possible timetable that we can to provide a limited train service on both strike days.”
But passenger Thomas George tweeted: “Beautiful day for a rail strike! I’m wet, late and fed up. #RailStrike #MerseyRail”
According to Southern, the industrial action on 10 July is “not expected to have any further affect on services”.
Passenger DoctorY tweeted: “Another day, another packed sardine train journey with #southernrail”
An ASLEF union driver overtime ban is in force and a revised timetable axing a quarter of services, was brought in on 28 June.