Auckland rail commuters counting down to next week's introduction of all-electric train services are being warned that reliability might take months to follow.
Next Monday will be the first weekday without the ageing diesel fleet on Auckland's main commuter lines, following an electrification upgrade costing more than $1 billion.
But Auckland Transport says a range of reliability problems which hit an all-time low in March will not end overnight.
Punctuality fell to 73 percent on the Western Line, but has since clawed back to above 82 percent across the entire network in the first week of July.
The network has been hit by the declining reliability of the outgoing diesel fleet, teething troubles on the high-tech Spanish-built electric trains, signal and track problems, and staff coming to grips with the new technology.
Figures supplied to Radio New Zealand show a decline in the number of faults on the new trains over a three month period, even though the size of the fleet in service is growing.
Problems being worked on include doors not operating if the train stops on a tilt, and intermittent faults on both the power system, and track sensors - all being dealt with through software upgrades.
Auckland Transport general manager of public transport Mark Lambert said those were normal bedding in problems, and were being dealt with by trainmaker CAF.
"We are seeing a significant improvement in the performance of those trains, and as CAF are identifying faults they are being fixed quite quickly," he said.
"Having said that, you'd expect for complete bedding in of new technology, to see that come right over 6-12 months."
Other problems have occurred as drivers are trained on the high-tech controls. Some problems require a simple re-set procedure, but at times new drivers have struggled, compounding delays.
Mark Lambert said as more trained drivers came through, and became more familiar with the electric trains, those problems could disappear over six to eight weeks.
Diesel problems will largely disappear with the removal of all but a handful of the most reliable diesel units, which will shuttle between Papakura and Pukekohe on the southern end of the network.
Signalling and track network problems will remain part of the mix facing rail commuters, with the number of failures remaining constant over three months to reach 117 in May - showed the most recent data provided by Auckland Transport.
However, rail patronage continues to climb strongly, up more than 21 percent over the past year, and on the verge of breaking the 14 million annual trip-threshold.