As it happened: Australia's worst rail disaster

Forty years on, the day remains "crystal clear" in Rob Garner's mind.

On his way to work in Sydney's CBD, he had been standing in carriage three shortly before the train he was on derailed near Granville station about 8.10am on January 18, 1977.

Moments later, the 170-tonne Bold Street Bridge collapsed on carriages three and four, killing most of those inside in what remains Australia's worst train disaster.

In all, 83 people died and 213 were injured in the tragedy at Granville.

"Where I had been standing, no one in that area survived. Someone was looking after me that day," Mr Garner recalled.

On Wednesday morning, survivors, victims' families and those who rescued passengers will be joined by NSW Premier Mike Baird, Transport Minister Andrew Constance and NSW Governor David Hurley at Granville to commemorate the 40th anniversary of the train disaster.

"It's a chance to remember those who were not as fortunate as me, who were seated where I was standing and lost their lives through no fault of their own," Mr Garner said.

Barry Gobbe, who was one of the first ambulance officers on the scene and later wrote a book about the disaster, said it was important to gather to remember the tragedy, especially for victims' families.

"Some of those families have never gotten over this tragedy," he said.

"Those people have never had closure. They have just gone on living their lives. In those days they were ignored by the government and by the public."

The NSW government will make an apology in Parliament to the families of those who died in the disaster once Parliament resumes next month.

Doug Reckord, whose late father Ian was a passenger on the train and later recognised for his efforts at the scene, said an official apology was a positive step by the government.

"People could say it has been a long time coming but ... people will welcome the recognition," he said.

"[The disaster] must just have been an absolutely horrific experience for anyone on the train and emergency services."

Relatives will begin reading out the names of those killed in the disaster at 8.10am on Wednesday, which will be followed by a church service at St Marks, a throwing of roses at the Bold Street Bridge and a wreath-laying ceremony attended by senior politicians.