Town said the $400 million gap in the Auckland Transport Alignment Project was a conservative figure and the aim was to stretch and accelerate transport spending.
Town said a 2.5 per cent rates rise cap over an extended period of time would set challenging targets, but officers would back themselves to achieve them.
Setting rates rises at 2 per cent - favoured by some councillors - becomes "unmanageable without you having very important and honest conversations about trade-offs", said Town.
Goff said the council was considering other revenue options, such as a fuel tax or a congestion tax.