Tranz Rail has been ordered to cut the speed of passenger trains to 40km/h over long sections of track in hot weather because of the risk of track buckling.
The restrictions have been imposed by the Land Transport Safety Authority after the Overlander express, between Wellington and Auckland, hit a sectionof buckled track near Te Kuiti last week. The train was travelling at 90km/h at the time.
No one was hurt, but the incident has prompted an inquiry by the Transport Accident Investigation Commission.
Tranz Rail has heat sensors at various points along the tracks which activate an alarm when air temperatures reach 30 deg C. But there were no gauges along the section at Te Kuiti.
LTSA spokesman Andy Knackstedt said that until now there were speed restrictions only along small sections of track where alarms were activated.
But as a result of the Te Kuiti incident, passenger trains would now be required to slow to a maximum of 40km/h over an entire geographic area, not just a small section of track.
Goods trains will also be required to slow to 40km/h over specified sections.
The LTSA is also hiring Australian contractors to look at track safety arrangements and plans for further cuts in track maintenance staff.
In December, Tranz Rail awarded a three-year $150 million contract to Australian-owned Transfield Services.
In advance of the switch this month, Tranz Rail gave redundancy notices to 92 of the 500 staff working on track maintenance.
However, the LTSA said it would not give its approval unless "the infrastructure is safely maintained".
