MACQUARIE Bank's North American briefing once again provided an upbeat assessment of the potential of the huge US market.

The tollroad opportunity alone is worth at least $US50 billion ($66.6 billion), Macquarie's North American operations head Murray Bleach said.

"I have a strong belief that the major airport market will break in the US," he added, pointing to billions-worth more of potential opportunities.

Chicago's second airport, Midway, is one reportedly expected to come on the block soon.

Macquarie is also in the process of raising a substantial wholesale infrastructure fund to take advantage of the opportunities. Mr Bleach said that Securities and Exchange Commission regulations prevented him saying how much money the Macquarie Infrastructure Partners fund had raised so far.

As if to highlight the US's abundant infrastructure opportunities, Bloomberg reported on Friday that Macquarie, the Carlyle Group and Babcock & Brown were planning a $US2 billion-plus takeover of SSA Marine, a ports operator.

Separately, Macquarie has reportedly been seeking to buy the ports that American legislators forced Dubai Ports World to divest after its acquisition of Britain's P&O Ports.

Most analyst valuations are at least partially based on the emerging opportunity presented by the US market.

Mr Bleach noted last week that Macquarie had 85 bankers in North America working on sourcing new transactions and 40 bankers managing the properties Macquarie already owns.

Most of the bank's newly arrived competitors in the area only have six to eight bankers, Mr Bleach said. But Macquarie is aware of the threat posed to its business model by the growth of US economic nationalism.

Macquarie Infrastructure Group chief executive Stephen Allen has said the main concern for Indianans in the $US3.8billion sale of the Indiana Toll Road to MIG and its Spanish partner Cintra was the question of foreign ownership.

MIG is reviewing its corporate structure in a process that looks likely to lead the tollroad operator to list in the US.

Part of the rationale for a move to the US would be to allow MIG to dip into the deep US markets, which could offer the liquidity for really big deals.