The Rail, Maritime and Transport (RMT) union is staging the second of six scheduled 24-hour walkouts in a dispute over driver-only trains with ScotRail.
Traffic Scotland warned the M8, M9, M90 and Forth Road Bridge were busier than normal due to the strike action and also because of the start of the Royal Highland Show on the outskirts of Edinburgh.
ScotRail said its reduced timetable is “running well”, but thousands of passengers have been affected with around a third of services unable to run.
Trains between Edinburgh and Glasgow, Edinburgh and Aberdeen, and Glasgow and Carlisle are among 15 routes cancelled by the walkout.
The RMT is opposed to the extension of driver-only and driver-controlled services and balloted ScotRail conductors last month, saying it had not received the assurances it had sought on the issue from the company.
These included guarantees that the safety role of conductors and their role in operating train doors would not be reduced or abolished.
Guards at the RMT backed walkouts by a ratio of 3 to 1, prompting the union to announce seven days of strikes during June and July.
General secretary Mick Cash said: “RMT members should not have to face the risk of their role and responsibilities being reduced and undermined.
“The workforce also know only too well that there is a very real threat to passengers of watering down and wiping out the safety critical role of the guard on these ScotRail services. That is a lethal gamble with basic rail safety.
“The union remains available for serious and meaningful talks but the ball remains firmly in ScotRail’s court.”
ScotRail managing director Phil Verster said the strike is ‘’totally needless’’.
He said: ‘’Tens of thousands of our customers will be disrupted and hundreds of our own people will be hit financially as a result of their intransigence.
‘’The public will be astonished to hear that this is a strike only about who opens and closes doors on trains, nothing more.
‘’The RMT are being, at best, disingenuous when they tell people that we are trying to have driver-only trains. We are not.”
Scotland’s transport minister Humza Yousaf urged both sides to keep talking and described the action as ‘’very disappointing’’.