KiwiRail says checks on 25 Ganz Mavag trains that were examined after a derailment in Wellington have revealed no problems.
About 350 people were on the 7.43am train from Porirua on Monday when a rear carriage came off the tracks, blocking lines into the capital's main station and causing major disruption to commuters.
The last carriage of the Ganz Mavag was forced from the rails, its floor pierced by a steel reservoir tank that apparently fell from a carriage and got wedged in the tracks.
Four people received minor injuries, though none required hospital treatment.
KiwiRail and the Transport Accident Investigation Commission have launched separate investigations into the accident.
KiwiRail general manager of passengers Deborah Hume says a report that the train went through two tunnels with a tank dragging on the ground would be part of the investigation.
She says KiwiRail will be asking staff why the problem wasn't noticed earlier.
Transport Accident Investigation Commission spokesperson Peter Northcote says the damaged train has been taken to a workshop where to be examined by its investigators and KiwiRail engineers.
He says they will also be gathering maintenance records and interviewing witnesses.
Mr Northcote says the commission's investigation is expected to take one to two years.
A rail engineering consultant says the derailment followed a delay to major maintenance work on the capital's train fleet.
Former KiwiRail engineer Randall Prestidge, now a freelance consultant, told Radio New Zealand's Morning Report a full service of the older trains was due a few years ago.
But they were instead sold to the Greater Wellington Council, which cancelled the maintenance and ordered new trains.
Mr Prestidge says the derailment could have been worse if a cylinder had ruptured or the train had hit another travelling in the opposite direction.
Services were running to schedule though KiwiRail said there was reduced capacity on some trains.