Trains have been cancelled in Scotland, after guards and drivers belonging to the transport union RMT went on strike.
The walkout is set to last for a total of four days, ending at 6pm on Thursday (April 15).
First Scotrail said 95% of trains will run, with bus replacement services on routes affected by the strike.
The dispute is over the staffing of trains on a £300m new rail line linking Glasgow and Edinburgh via Airdrie and Bathgate.
Under First Scotrail's plans, drivers will be able to open and close the doors on the trains, which means only ticket examiners will be employed onboard. RMT argues this is unsafe.
Bob Crow, RMT general secretary, said: "First Scotrail and the Scottish government are still refusing to face up to their responsibilities to the travelling public and their staff and are prepared to slash corners on rail safety in the dash for cuts and the drive for profits."
First Scotrail said: "Driver door operated trains with ticket examiners are safe and have been proved in all conditions for more than 25 years. 56% of ScotRail journeys are already made on this basis.
"It would cost £1.4m to convert the trains to allow conductors rather than drivers to open and close the doors. This is an unnecessary cost - and would make journeys longer. The work would also delay the re-opening of the route.
"No-one is losing their job and current terms and conditions are guaranteed."
www.scotrail.co.uk www.rmt.org.uk