No further action is being taken against rail operator Northern over last year's timetable change fiasco which led to weeks of disruption.
The news emerged as Govia Thameslink Railway was fined £5 million by the rail regulator over its poor communication with passengers during the chaotic introduction of a new timetable.
But the Office of Rail and Road concluded that Northern had "taken reasonable steps" to communicate with passengers over the timetable fiasco, so the company was let off with no further action.
The ORR said that Govia Thameslink "failed to provide appropriate, accurate and timely information" amid severe disruption on its Thameslink and Great Northern routes for eight weeks following the launch of the May 2018 timetable.
Some trains were permanently removed from the timetable but this was not made clear to passengers for several weeks, according to the ORR.
Other trains were removed or cancelled on a daily basis, leading to a "severe lack of certainty for passengers up until the point of travel", the ORR said.
The investigation also found that inadequate internal communication within GTR often left station staff with "little or no information" to help passengers.
These failures left passengers with "very little notice or certainty" about what trains would run.
A separate ORR investigation into Northern, which operates services across Lancashire and northern England, found in many cases passengers were given "inadequate information" in the two weeks that immediately followed the timetable introduction.
But the regulator concluded that the firm "subsequently took reasonable steps" to rectify this, meaning that no further action will be taken in relation to the issue.
The ORR has written to all train companies and Network Rail to require them to review their crisis management plans and ensure appropriate arrangements exist for assisting passengers with disabilities in times of disruption.
Stephanie Tobyn, a deputy director at the regulator, said: "The disruption experienced by many passengers as a result of the May timetable introduction was awful.
"When disruption happens, poor quality information makes an already difficult and frustrating situation worse.
"The exceptional circumstances that followed the introduction of the timetable meant that providing perfect advance information for passengers was from the outset an impossible task and GTR's overriding focus was on providing as much capacity as it could to meet customer demand.
"However persistent and prolonged failures in information provision meant that passengers couldn't benefit from the operational improvement it was trying to make."
Anthony Smith, chief executive of watchdog Transport Focus, said: "Passengers were badly let down when the new timetable descended into chaos on some Govia Thameslink Railway and Northern routes, and information was often poor.
"This £5 million fine for Govia Thameslink should be a wake-up call to train companies that accurate passenger information really matters.
"It is important that the money from this fine is reinvested to benefit those passengers who suffered last year."
The number of trains cancelled each day by GTR and Northern following the May 2018 timetable launch reached up to 470 and 310 respectively.
Train companies, government-owned infrastructure company Network Rail and Transport Secretary Chris Grayling were all blamed for the chaos.
Industry body the Rail Delivery Group insists it has "learned the lessons" from the disruption ahead of another timetable change in May.
A spokesman for Northern said: "We welcome the ORR's findings on Northern and are reviewing the detail of the investigation report.
“Last year was very difficult for our customers for well-known reasons, particularly the ongoing impact of delays to infrastructure upgrades.
"This meant we did not meet people’s expectations and we are sorry for that.
“Following the experience of 2018 Northern has made improvements, and we continue to invest in better customer information systems and processes.
"We are determined to deliver a better service for our customers in 2019 with improved punctuality, the delivery of new and refurbished trains, and better stations."