For the past several years, the car festival which attracted more than 105,000 people to Exhibition Park in Canberra in January has started several days after New Year's Eve.

That allowed authorities a necessary breathing space between the two busy periods.

But Summernats organiser Chic Henry is staging the festival's preliminary events on New Year's Eve, with the main program beginning on New Year's Day and continuing until January 4.

This year's event was marred by crowd trouble when hundreds of young men, many of them drunk, marched through the showgrounds chanting and harassing women.

At one point during the disturbance, up to 50 police officers gathered at marshalling points outside the showgrounds, ready to intervene. There were reports of a violent brawl at a bar inside EPIC, and two marshals were allegedly caught on camera punching and kicking a festival-goer.

A NSW man is facing criminal charges over the attack.

In the aftermath of the trouble, police foreshadowed an increased presence at Summernats 2009.

It will open on the morning of New Year's Eve with entrants and friends gathering at the showgrounds and partying into the night, with the festival's full program beginning on January 1.

A spokesman for Attorney-General Simon Corbell said ACT Policing was aware of the event's timing and had started planning.

ACT Tourism Industry executive director Joseph Griffiths said starting Summernats on the busy New Year's Eve would was problematic.

''This would cause problems for the hotel operators around town because New Year's Eve is already a problem time for them,'' he said.

''If then you have a Summernats crowd getting around town, then it's going to be very interesting.''

Mr Griffiths said Summernats provided maximum value for the tourism industry when it began several days after the city's New Year's Eve revelry. ''Summernats is an important drawcard for the industry, no doubt about that, but it works better a few days after New Year's because it gives everyone a chance to clean up and get that period out of the way,'' Mr Griffiths said.

Opposition police spokesman Brendan Smyth said the decision to allow Summernats to begin on New Year's Eve had been made without consultation.

''Then there's the security side of things,'' he said. ''That's because it's always a big night for the police, with a lot of parties going on around the city, and this is just going to stretch resources even further.''