The Government says a new bridge across the Waitemata Harbour in Auckland would be $1.4 billion cheaper than a tunnel.
Despite the price difference, the Government has not yet decided which which option to back.
Traffic on the Auckland Harbour bridge - currently 168,000 vehicles a day - is expected to rise by about 40,000 vehicles a day by 2041.
The Government wants a new crossing built in the next 20 years to cope with demand.
A report issued on Monday says a new bridge would cost about $3.9 billion, while a tunnel crossing would cost about $5.3 billion.
It says the consent process for a new bridge could take one to two years longer than for a tunnel because of its visual impact.
However, constructing a bridge would take one to two years less than a tunnel.
Transport Minister Steven Joyce says Auckland residents need to be aware of the costs and benefits of each option.