The dispute, which has now dragged on for nearly a year in parts of the network, centres around the union's opposition to the proposed move to driver-only-operated (DOO) or driver-controlled operation (DCO) trains, which would see services be operated without a guard and could potentially, RMT claims, compromise passenger safety - although this has been widely disputed.
Train operators are looking to see off further strike action after a 24-hour walkout was held on Southern, Northern and Merseyrail yesterday in disputes over the role of the guard.
"This strike is about safety and about putting the welfare of the travelling public before the profits of the private rail companies".
The strikes are over the future role of rail guards, with the companies moving towards driver-only operations (DOOs).
Merseyrail had hoped to run more trains but had to change its contingency plans "because train drivers, who are not part of the industrial action taking place on the Merseyrail network today, have decided not to cross RMT picket lines".
The RMT strike on Southern is the 30th since a row over the role of conductors flared nearly a year ago. "They are a credit to their local communities and to the entire trade union movement".
It is thought the strike will result in Northern Rail running around 40% of its normal timetable during this period.
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He said: "The RMT action is absolutely solid, with pickets out in force at key points and the response on the ground has been wholly positive". "This action could have been avoided if Arriva hadn't back pedalled from earlier pledges to retain the guard".
The union says it'll make trains more risky.
There'll be NO trains OR replacement bus services between Morecambe and Lancaster.
Frustrated commuters giving up on cancelled or delayed trains and finding alternative routes to work is also expected to create chaos on the roads this morning.
There will be just just four trains running from Barrow to Lancaster and back.
She said: "I'm not anxious about getting stuck in Manchester there are always buses to get back on and if I can't get a bus I'll ring my partner to come and pick us up the strike won't ruin our day".