The shortfall of parking was so bad at the National Museum at a recent event that visitors from Sydney gave up looping the area after half an hour and left, a parliamentary inquiry heard on Friday.

Leaders of the ACT's most well-known and respected galleries and museums have told the National Capital Authority of their parking woes. The popularity of the National Museum exhibition had caught it by surprise and left it scrambling to find space for overflow parking.

The authority's chief planner Andrew Smith told the inquiry into Australia's cultural institutions the National Library and the National Gallery had also encountered problems finding overflow parking for popular exhibitions.

"When any of the instititutions have an event or blockbuster that grabs the community's attention, they have to find ways to accommodate that demand," he said.

Most expanded opening hours or tried finding additional places where their visitors could park if exhibitions became popular.

The authority and National Museum had talked about how to accommodate more cars at the next exhibition, and construction would begin on expanded parking within months.

The National Museum had only limited bus parking as well and discussions about the issue with the National Capital Authority had previously not come to a resolution.

Mr Smith said there was a need to centrally coordinate tourist buses visiting the museums and galleries, as the parliamentary zone became busy with them.

"At times, certain areas there's a lot of pressure put on the infrastructure simply because there's no central coordination of arrival of visitor groups, and the physical infrastructure to accommodate those peaks doesn't exist, we'll have people turned away from those institutions."

Museum of Australian Democracy director Daryl Karp told the inquiry Old Parliament House had similar problems.

"As a cultural institution we don't have sufficient parking," she said.

Ms Karp outlined a vision, if the museum received all the money required to execute it, to create an open, grassed space at the building's front, move car parking to an underground area around the back at a possible cost of $20 million to $30 million, and create entrances to the museum from all sides.

A "boulevard environment" would run from Parliament House, to Old Parliament House, and finally to the Australian War Memorial. Parking to the sides of the Museum of Australian Democracy would remain but the front area would contain seating for performances.

The federal inquiry is probing Canberra's national museum and galleries as they grapple with millions of dollars in funding cuts, forcing them to find new revenue and raising fears that government neglect could leave them forgotten.