Network Rail has been strongly criticised by regulators for its handling of Scottish timetables.
An investigation by the Office of Rail and Road (ORR) found "numerous errors" in its winter timetable.
The causes included a lack of quality assurance and detailed planning.
The rail regulator said, external it was the third time in recent years that Network Rail, which provides facilities to ScotRail and other operators, had caused timetabling problems.
However, it added that fewer passengers were disrupted and performance had improved recently.
The ORR said it would be closely monitoring the way Network Rail handled timetable changes involved in a major re-development of Queen Street Station in Glasgow.
The rail regulator's report also criticised Network Rail for its handling of services in two English regions - Southern and GTR - for which it was fined £2m.
ORR chief executive Richard Price said: "Our investigation has identified important issues that Network Rail, working with operators, needs to address to improve performance for passengers on these routes.
"Our analysis shows that the company needs to develop a much better understanding of the impact of timetabling on the reliability of services and on rail users."
Network Rail apologised to passengers for "disruption and frustration".
A spokesman for Transport Scotland said: "Last year's performance levels fell some way below the standards set by the Scottish government and expected by passengers.
"We note the conclusions of the ORR's investigation on the reasons behind this and expect all recommendations to be reflected in full within the planning processes established under the new ScotRail Alliance."
- Published10 August 2015
