Plans to get people to and from the London 2012 Olympics are "robust" and will not suffer from gridlock, a Games transport chief has told MPs.
Public transport will play an important role in 2012
Olympic Delivery Authority (ODA) transport boss Hugh Sumner said key schemes would be ready well in advance.
He added that extra train capacity and the fact that many people would be on holiday, would help the system to cope.
But MPs were told boat companies were reluctant to buy extra river boats to transport people to the Games.
The Commons Transport Committee were told that plans were generally 12 to 24 months ahead of what the International Olympic Committee expected.
ODA Construction Director Howard Shiplee denied that planners were a year behind on construction.
And Mr Sumner said key schemes being managed by London Underground's PPP (public-private partnership), such as extending the Docklands Light Railway, had been started early.
But his comments that other upgrades on the District and Hammersmith and City lines would not affect the Games were questioned by the committee.
Labour MP Clive Efford asked: "Aren't they necessary in terms of capacity if the system is failing?"
He said summer breakdowns had a "domino effect" causing gridlock across the Tube and displaced commuters could end up using up the extra space created for 2012 spectators.
He asked why two park-and-ride schemes, one on the M11, the other on the M25, had been discarded and "nothing significant" outlined for transporting people on the Thames.
"Aren't you putting all your eggs in one basket and in danger of, if there is a problem on the system, you will actually have log jam and be unable to use alternative routes?," Mr Efford asked.
Mr Sumner said the ODA was "committed to delivering reliable and robust transport" and was looking at alternative park and ride sites.
On river transport, he said some companies had said they were reluctant to commit to buy extra craft, but he said he was still hopeful that the river would play a major role.
Mr Sumner said there was extra capacity on some trains out of Liverpool Street and Fenchurch Street stations, heading east outside peak hours, should there be a block in the system elsewhere.
He said by using trains, the Tube, the DLR, buses, cycling, coaches and footpaths - they would not be putting "all our eggs in one basket".
And the Games, due to start on 27 July 2012, would take place at a time when many commuters would be on holiday - and more would take time off to go to the Games themselves, relieving pressure at rush hour.
But he could not guarantee there would be no road works during the Olympics and said contingency plans still needed to be "refined and detailed" with operators over the next six years.
Mr Sumner said: "I'm confident that the key schemes that are necessary to deliver transport for the Games will be completed well in advance of the Games."