Auckland ratepayers are paying the bulk of a $1.8 million bill for traffic management costs at the Rugby World Cup under a confidential agreement signed by former council bosses.

The heads of the region's eight old councils agreed for ratepayers to pay most of the traffic management costs at Eden Park and North Harbour Stadium, contrary to the normal practice of rugby users meeting all costs.

The costs are part of a $35 million bill for running costs at the Cup. Ratepayers are also giving $65 million for infrastructure, including $10 million towards upgrading Eden Park.

Under a "host region agreement", signed in 2008 between council bosses and Rugby New Zealand 2011, ratepayers will pay $520,000 of the $828,000 for traffic management at the two stadiums. Rugby NZ's share is $308,000.

The agreement also commits ratepayers to a further $972,000 to cover all traffic management costs for the central business district, fan zones and public open days at training venues.

Rugby World Cup event manager Rachael Dacy said the agreement was a "commercially sensitive document" that Rugby NZ did not want publicised.

Rugby NZ executive Nigel Cass said its contribution was part of the agreement negotiated at the time Auckland tendered to be a host city.

"This is the same for every city that tendered to host RWC 2011 matches. All are making various contributions to tournament costs in recognition of the benefits they expect the event will generate for their regions."