The cost of running Auckland's public transport has quadrupled in 10 years - while patronage rose by little more than 60 per cent.
The discrepancy was revealed to Auckland Council's transport committee in a staff report which promised greater efficiencies from a new operating model to be based heavily on a redesigned bus network.
A graph in the report showed an annual cost escalation, although without adjustments for inflation, from about $45 million in 2001 to almost $180 million last year.
Annual public transport patronage for the period increased from about 43 million passenger trips to just over 70 million.
But the report, by principal council transport planner Joshua Arbury, said the trend had begun to reverse, with costs falling last year at the same time as patronage rose by 9.6 per cent to what Auckland Transport says is its highest since 1958.
Factors contributing to the cost escalation included the revival of Auckland's rail network - on which annual patronage has more than quadrupled since 2002 to 10.8 million passenger trips - and a significant renewal of bus fleets.
But average public transport trips lengthened over the past decade, meaning the level of council and Government subsidies increased more modestly than the costs surge.
Mr Arbury said the average bus trip - excluding Northern Busway travel - ran to 6.6 km compared with 16.5km on trains, which provided far greater road congestion relief per passenger carried.
His report blamed withdrawals by bus operators from commercially registered routes between 2006 and 2008 for an annual subsidy increase of $15 million to $20 million to retain service levels.
That funding "shock" led to a legislative change which will allow councils and Auckland Transport to draw up more comprehensive network-wide plans to improve service efficiencies.
With a major exercise planned to that effect in Auckland, the report warned it was highly unlikely the Government's contribution to public transport services could keep increasing as rapidly as in recent years, especially for buses.
Mr Arbury told the councillors that this highlighted a need for greater efficiencies to avoid having to spend "a huge amount of money" to meet an Auckland Plan goal of doubling annual public transport patronage to 140 million passenger trips by 2022.
He pointed to expected efficiencies from the electronic Hop card, which is due to be rolled out by the end of this year across the region's bus, rail and ferry fleets, and a "clean slate" review by Auckland Transport of all public transport routes.
The Hop card will ultimately remove any extra fare cost of transferring between buses, trains and ferries over given distances, although Auckland Transport intends introducing a 50c transfer discount initially.