The wife of a train driver killed in a catastrophic crash on Melbourne's outskirts says she'll never forgive his employer, as the company pleaded guilty to breaches of rail safety laws.

John Kennedy was in command of an XPT passenger train travelling from Sydney to Melbourne when it derailed at high speed at Wallan on February 20, 2020.

Mr Kennedy and his co-worker Sam Meintanis were killed, while a further 61 people were injured.

On Friday, rail operators NSW Trains and the Australian Rail Track Corporation admitted in court that they had failed to put in place basic safety measures which could have prevented the tragedy.

In a statement read out to the Melbourne Magistrates' Court, Mr Kennedy's wife, Jenny, said she learned about the accident through media reports, and that it took NSW Trains several hours to confirm her husband had been killed.

"It is impossible to put into words how it felt being the last person to be told of his death," she said.

"I felt so let down and abandoned by NSW Trains, who John was so loyal to for 40 years."

Mr Meintanis's partner, Naomi Bruce, said she had lost "the one person I did everything with".

"Sam went to work and never returned home," she said.

The court was told the train was travelling about 100 kilometres per hour over the speed limit on the section of track where it derailed.

It was an area where trains usually travelled at high speeds, the court heard, however the driver — Mr Kennedy — had not realised he was being diverted to a section of track where the maximum limit was just 15kph on entry.

Mr Kennedy, a driver with four decades of experience, was not aware authorities had made the track change the previous night.

Prosecutor Sally Flynn KC said that information was contained on a piece of paper in the driver's cabin, but no verbal checks were made with Mr Kennedy by network controllers.

Magistrate Brett Sonnet said most people would expect other basic safety measures to have been in place, such as flashing lights and signs to warn drivers of the reduced speed limit.

"It's perplexing why portable signs were not erected along the way which would have given John Kennedy the opportunity to reduce the speed of the train," he said.

Lawyers for both companies apologised to the victims and their families.

Other failures were identified by the Australian Transport Safety Bureau, which conducted a detailed investigation into the crash.

In a NSW budget estimates hearing on Friday, the state's transport minister, Jo Haylen, said the train operators were focused on making improvements and that safety "must always be our number one priority".

"As a transport team, we will continue to always look for opportunities to do better," she said.

The rail operators are facing potential convictions and fines as high as $1.5 million.

Magistrate Sonnet said he would deliver the sentence on April 3.