An accident report says a runaway train incident during rush hour in Auckland highlights sub-standard maintenance of rolling stock.
In October 2006, a train carrying 12 passengers travelled for more than half a kilometre without its driver in Auckland city, after he got out to investigate why the emergency brake had come on.
It stopped only nine seconds before reaching points between Britomart and Newmarket.
The Transport Accident Investigation Commission says the potential for a derailment was significant as the train would have arrived at a curved stretch of track travelling 60% faster than the speed limit.
The commission has recommended the New Zealand Transport Agency assess how widespread maintenance shortcomings are.