RMT members gathered at Glasgow's Queen Street station on the last strike
Hundreds of Scottish rail workers are taking part in a three-day walkout.
The dispute between First ScotRail and the RMT centres on plans to employ ticket examiners rather than conductors on the new Airdrie to Bathgate line.
The RMT and ScotRail accused each other of "intransigence" after talks involving the conciliation service Acas broke down last week.
ScotRail said it was operating 95% of services during the strike, which started at 0001 BST on Monday.
The union has argued conductors, or guards, are best equipped to deal with serious incidents and claims the plan will "jeopardise passenger safety".
However, First ScotRail has dismissed the safety concerns and insisted the trains will be no different to those which have operated in Strathclyde for 25 years.
Steve Montgomery, ScotRail's managing director, said: "We have run even more services than during the last strike. At least 95% of services were provided, with the expansion including all Glasgow-Oban trains. It was business as usual for Scotland's railway.
"Our contingency plans were such that almost all our customers will not have noticed there was a strike."
"There were some service revisions due to the RMT's bid to cause as much inconvenience as possible to our customers. However, we ensured the vast majority of travellers were unaffected," he added.
The company said a number of rural services would be replaced by buses and a "small number" of train services have been cancelled.
RMT general secretary Bob Crow 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.
"I repeat my call for a face-to-face meeting with First Minister Alex Salmond to resolve this issue and to get the company to comply with their obligations in respect of the guards."
There will be one train a day running between Inverness and Kyle of Lochalsh, with all other services being replaced by buses.
Buses will also replace trains between Inverness and Wick, and Kilmarnock to Stranraer and Girvan.
A reduced service will run between Edinburgh and Perth.
There will also be minor changes to services from Kilmarnock to Dumfries and Carlisle, between Glasgow and Edinburgh and Alloa, Dunblane and Perth, and on the Fife Circle and Newcraighall and North Berwick services from the capital.