London's transport infrastructure is still "one of the biggest risks" to the smooth running of the 2012 Olympics, according to a report released Friday by local city government.

Citing delays to upgrades of a London Underground rail line near the Olympic Park, London Assembly transport committee chair Val Shawcross said that the city's aging transport network could struggle under the load of a predicted 5.3 million extra visitors during the Summer Games.

"In 2012 London is facing extreme demand placed on a network already creaking at the seams," Shawcross said in the report. "This is not just about spectators and visitors being able to get to and from events; Londoners will need to go about their everyday business too."

London organizers have described the 2012 Olympics as the "public transport games," with spectators urged to travel to venues by Underground, bus, bike or foot.

The report, which is designed to identify problems early, said that most of the 30 planned improvements to London's transport infrastructure have been completed or are on course for completion this year.

But improvements to the London Underground Jubilee Line specified in London's original bid document are behind schedule. Originally expected to be completed in December 2009, the city's transport body now predicts that it will have completed the work by June this year.

The assembly transport committee also suggests that about a third of London residents may need to change their route, time or mode of travel because of the extra congestion.

"Spectators and Londoners will also need to respond positively to 2012 travel advice," Shawcross said. "In the run up to previous games, host cities have often launched publicity campaigns or 'the big scare' to encourage people to change their travel habits."

A 20 percent reduction in traffic is hoped for in addition to the 10 percent drop typically seen in London during August, but the report acknowledges that is ambitious.

On the nine days forecast in the report to be the busiest of the 2012 Olympics, there will be as many as 650,000 tickets available for events across London. With organizers aiming to eliminate all private journeys and get all visitors onto public transport, the report said that will create 1 million extra journeys.

"The travel hotspot areas include two of London Underground's busiest stations — Victoria and King's Cross — where control measures are already required almost every day during peak hours to manage overcrowding and allow the stations to operate safely," the committee said.

The busiest days are predicted to be Aug. 3-4.

The committee noted that organizers turned down requests by local councils to reduce the number of those entitled to use dedicated Olympic lanes on the city's roads.