On Monday 11 October 2004 at about 0007, the sixth wagon on Train 244, a Wellington to Karioi express freight service, derailed at 4.458 km on the North Island Main Trunk line, inside Tunnel 1 after the right wheel on the leading axle of the leading bogie fractured. The train travelled a further 4 km before the locomotive engineer looked back along his train, saw sparks and stopped the train that was by then inside Tunnel 2.
The derailed wagon caused some minor damage to the rail bridge over State Highway 1 at Ngauranga Gorge and to ground-level signalling equipment inside Tunnel 2.
The safety issues identified were:
• the suitability of the wheel profile used on the dedicated Wellington to Karioi ZH wagon fleet
• the overheat code standard used to determine when a wheel should be withdrawn from service.
As a result of the actions taken by Toll NZ Consolidated Limited, no safety recommendations have been made.
