Motorists will be warned to avoid central London and areas around all Olympic venues from mid-July onwards, with transport chiefs predicting large scale congestion in the fortnight before the opening ceremony as a deluge of athletes, officials and media arrive.
The crowds that have turned out around the country to greet the Olympic torch have increased the concerns of Olympic transport chiefs about the scale of the challenge in the runup to the Games.
Drivers will also be told to avoid the area around the 109-mile Olympic Route Network (ORN), making large areas of London an effective no-go area for six weeks from mid-July.
Since London won the right to host the Games in 2005 its crowded transport infrastructure has been an issue for organisers and critics.
Independent traffic management experts have warned of the danger of a perfect storm of problems around the opening weekend, but the London mayor, Boris Johnson, points to £6.5bn of investment in the transport system and has linked the unfounded "paranoia" to that surrounding the millennium bug in 1999.
A series of specific changes to the road system in and around London are being unveiledon Tuesday, including the reopening of the much criticised M4 bus lane as a Games lane from the weekend of 14 July.
"In a normal July you'd see traffic levels drifting off slightly as you ease into summer and things get easier on the roads, said Garrett Emmerson, chief operating officer, surface transport at Transport for London.
"This July is going to feel more like the runup to Christmas.
"Traffic is going to get heavier as more and more Games activity takes place. We've got to change London's network to cope with that."
When 20,000 members of the media beginning to arrive in the second week of July, traffic flow in the busy Kingsway tunnel will be reversed to "assist movements" at the media hotel hub in Bloomsbury and a series of signal changes will be made.
"It's very clear that London is going to be very crowded," said Emmerson. "That is going to start from the beginning of the week before the Games."
From 21 July, when the Olympic torch is due to arrive in the capital, the Olympic Route Network – including 30 miles of dedicated lanes – will be introduced, simplifying junctions, removing pedestrian crossings, banning right hand turns and removing parking bays. The full network will come into effect on 25 July, when the torch enters central London.
Recent serious problems with the Jubilee and Central underground lines and complaints about overcrowding during the jubilee weekend have renewed concern over transport during the Games.
Transport for London officials insisted the extended bank holiday was encouraging and proved that motorists would heed messages to stay out of central London, with traffic down 40%.
"People now get there is something coming down the tracks and they need to prepare for it," said Emmerson. "We now need to move into what they need to do about it and when."
He said TfL's Get Ahead of the Games website had had over a million hits.
Emmerson said TfL was "now very confident" about major employers and businesses that needed to change their delivery plans. "We now need to move them into operational phase."
According to TfL's predictions, there will be around 1 million extra people in London over the course of the Games making 3m extra trips.
But the effect will be mitigated by a reduction in the number of non-ticket holding tourists visiting London. The biggest concerns are over "hotspots" on particular days.
TfL has warned that rail and tube users face delays of more than half an hour at key stations, with London Bridge among the worst affected.
London 2012 organisers and local authorities will start to introduce parking restrictions in mid-July. The handful of tow trucks that usually operate in the capital will swell to about 70 at Games time to remove cars that block the ORN and restricted parking zones.
TfL plans to employ 3,000 back office staff on the street in magenta tabards to provide travel advice. Each will be given an iPad to allow them to deliver up to the minute advice.
