Today’s launch of ScotRail’s new timetable was marred by a series of cancellations caused by staff shortages.
The operator said the improvements would bring faster journeys, more seats and more services.
However, at least seven trains did not operate all or part of their scheduled journeys because of a lack of drivers.
This affected services between Edinburgh and Fife, Aberdeen and Inverness.
The disruption was compounded by a train fault cancelling another service on the Edinburgh-Fife line, and signalling problems - the responsibility of Network Rail - between Stonehaven and Aberdeen.
In addition, seven services on routes between Edinburgh, Glasgow, Aberdeen and Inverness ran without a catering trolley service because of a “shortage of train crew”.
Some of these were on journeys of nearly three hours.
However, there were no cancellations caused by staff training, which ScotRail had pledged to complete by today after causing dozens of trains a day to not run over several months.
The operator said three of today’s cancellations were caused by a driver being off sick - with no replacement available.
It said another four were due to a rostering issue.
ScotRail said two drivers “changed rosters from winter overnight and required sufficient rest time between duties”.
It said Sundays were "always problematic" because they were organised differently from the rest of the week.
The Scottish Conservatives said it warned of such problems.
Transport spokesman Jamie Greene said: “We have been warning ministers for months that poor workforce planning and driver shortages will inevitably lead to cancellations and disruptions on the network.
“Our concerns were downplayed repeatedly in the Scottish Parliament.
“Given that it takes up to two years to train a new driver, I suspect this is just the tip of the iceberg when it comes to further disruption and misery for ScotRail commuters.”
Scottish Labour transport spokesman Colin Smyth said: “This is not a good start to the much-hyped changes at ScotRail.
"Scottish passengers are fed up with delays, cancellations, overcrowding and inflated costs that go to the pocket of Abellio and not to improvements to services.”
A ScotRail spokesperson said: “We do have spares in driver rosters (shift patterns) to try and cover for these situations, where possible.
“Over 99 per cent of our services are planned to operate today.
“The introduction of the timetable changes will deliver even more improvements on Scotland’s railway, with the investment in new trains and infrastructure providing faster journeys, more seats and more services for our customers.
“We are now providing 115,000 extra seats every day since Abellio took over the franchise in 2015, and everyone across the ScotRail Alliance is working flat out to deliver the service that our customers expect and deserve.”
Improvements include more carriages on peak-hour services between Glasgow and East Kilbride and Barrhead.
The Edinburgh-Glasgow line via Shotts will be mostly operated by new electric trains, providing more seats on weekdays.
The faster-accelerating Hitachi Class 385 trains will also take over Glasgow-Lanark services.
They will operate all services on the Edinburgh and Glasgow to Alloa and Dunblane lines, speeding up journeys and providing more seats.
Weekday journeys on the Edinburgh-Glasgow main line via Falkirk High will be reduced to an average of 47 minutes compared to around 50, with more services completing the trip in 42 minutes.
There will also be extra trains on the Glasgow-Mallaig line.
ScotRail said an extra 20,000 seats a day were being added to trains, increasing the total by 115,000 - 23 per cent - to 625,000 since Abellio took over the franchise in 2015.