Motorists could be charged different rates for the London congestion charge depending on what time of day they enter the zone, under plans being considered by Boris Johnson.
One option examined by the mayor would mean motorists paying more to enter the central zone during peak periods and less at other times, to encourage them to avoid rush hour in the capital.
The idea of scrapping the fixed £8 daily charge and replacing it with an "intelligent" congestion charge system is based on a scheme in Stockholm, which introduced congestion charging after London first introduced it in 2003.
The mayor, who before Christmas admitted he was stung by his own system and fined after failing to pay on time, has also instructed Transport for London to set up an accounts billing system to make it easier for drivers to pay.
This could include either direct debit payments or an electronic chip system that picks up a car's entry into the zone.
A spokesman for the mayor said Johnson had absolutely no plans to scrap the congestion zone in central London, but was seeking to make the system "fairer" for motorists.
The spokesman said: "Since taking office the mayor has made it clear he believes the congestion charge makes a valuable contribution to reducing the number of cars in central London. But he has also made clear that he will consider ideas that could make the charge more effective and easier to pay for everyone affected by it.
"His election manifesto committed to introducing account-based payments to reduce the number of drivers clobbered by fines for failing to pay on the day. And a variation of charges according to the time of day was an option given when consultation took place on removing the western extension.
"The mayor has asked TfL to make the changes that could introduce account payments as soon as possible but the earliest they could be introduced effectively is 2010. Other improvements will continue to be discussed but at the moment there are no firm plans for their introduction."
IBM, the company that implemented the Swedish system, will take over the contract for congestion charging in London in November.
Currently drivers entering the congestion charge zone in London at any time between 7am and 6pm on weekdays pay an £8 flat rate on the day of travel, or £10 the day after travel.
Varying payments was one of the options proposed in a recent consultation exercise that asked Londoners whether they wanted to see the western extension of the charge scrapped, kept, or retained with modification. Voters backed abolition, a move which will be implemented next year subject to a formal public consultation on Johnson's transport strategy.
The London Chamber of Commerce and Industry welcomed the possibility of varying charges throughout the day.
Colin Stanbridge, the LCCI's chief executive, said: "These changes, if implemented, would make the c-charge fairer, flexible and more business friendly. Our latest research shows that 82% of retailers within the c-charge zone think that flexible charging would be good for their business. A system that means it is cheaper to drive in to the zone between the rush hours would attract more shoppers into London and provide a vital life line to our retailers."
But critics warned that London's "rush hour" is ongoing throughout the day in the capital.
Jenny Jones, a Green party assembly member, said: "The proposal to vary the charges for cars only makes sense if there is an actual rush hour. In reality the roads of central London are pretty much at their peak all day long. Figures from the first three years of the congestion charge show that the average speed during the morning and evening peak was 10.6mph, whilst the rest of the day it was 10.5mph. It would therefore make no sense to encourage more cars into central London during the day. The most likely result is more traffic and more pollution."
Labour's transport spokesperson on the London assembly, Val Shawcross, said: "Making it easier to pay is one thing, but a price cut would be a dangerous green light for more cars to come in and clog up central London. The mayor should be looking to make the best possible use of technology to cut congestion, make the system more efficient and improve London's urban environment. His vision for London is developing into 'motorist first, everything else second'."
Johnson's attempts to overhaul the congestion charge follows recent research which found that, although traffic inside the central zone had dropped since the scheme was first introduced in the central zone in 2003, congestion has risen back to pre-charging levels.
However, Transport for London says that congestion would be "significantly worse without the sustained traffic reductions brought about by the charge".
