London 2012: M4 Olympic Games Lanes come into operation
The first of the Olympic Games Lanes has come into operation on the M4.
The restrictions on the 3.5-mile (6km) stretch of the motorway between Heston and Brentford in west London will be in place from 05:00 BST until 22:00 BST.
Motorists could be fined £130 for straying into it. The road was reopened on Friday following repairs to a crack which appeared on the former bus lane.
Apart from official Olympics vehicles only black cabs are allowed to use the M4 Games Lanes.
Athletes and officials who have begun arriving at Heathrow Airport are using the lanes to reach the Olympic Village.
Transport for London (TfL) said there was a 10% drop in traffic in to central London on Monday.
Mayor Boris Johnson said: "London is as ready, in fact readier, than any Olympic city has ever been at this stage of proceedings and I think the IOC are bowled over by the success we have had in delivering the Olympic venues on time, under budget."
There will be 30 miles (50km) of Games Lanes in London, which will form part of the Olympic Route Network (ORN), most of which will come into effect from 25 July - two days before the opening ceremony.
'Far from happy'
The Games Lanes will be clearly marked and will operate alongside existing traffic, but all road users will be able to go into the lanes when they are not in use overnight.
Steve McNamara, general secretary of the London Taxi Drivers' Association, said black cabs were allowed to use the Games Lanes on the M4 and Park Lane and can pick up and set down in most lanes near the Games sites.
"We are also allowed to make right turns across a significant number of lanes throughout the ORN," he added.
"But we are far from happy with these lanes and we would question the need for them any time."
A TfL spokesman said: "The Highways Agency have confirmed to TfL in writing that licensed taxis will be permitted use of the M4 Games lane."
Kevin Delaney, head of road safety at the Institute of Advanced Motorists, said a breakdown or crash could lead to a "perfect storm".
Mr Delaney, who was former head of traffic at the Metropolitan Police, said: "The problem with the Games Lanes is that London's road network runs at, or very close to, capacity almost all day, almost every day of the year.
"Unless everybody heeds the advice to not drive, there are problems. Imagine if there is a situation where we have a breakdown or a crash.
"It would be like a perfect storm - the level of congestion that you would normally get would be magnified."
Earlier accidents on the M4 in Berkshire affected traffic heading into the capital London.
But a Highways Agency spokesman said: "The delays were a long way from west London and traffic in the area of the Games Lane was no worse than it is on any normal Monday morning."
On Sunday, Sport Minister Hugh Robertson said the authorities had plans to lift the restrictions on the lanes if there was gridlock.
The M4 had been closed between junctions two and three for about a week after a crack was found in the Boston Manor viaduct.
There were fears the repair work on the damaged flyover near junction two may not be completed in time for the Games Lanes to open, but the motorway reopened on Friday.
But restrictions imposed on vehicles weighing more than 7.5 tonnes, which had been in place since March when hairline cracks were discovered in some of the steel beams, are still in place.
The motorway connects west London to south Wales.