One year into the scheme to charge drivers in central London and mayor Ken Livingstone has plenty to smile about.
Traffic is moving faster, bus delays are down 50% and, for many drivers, paying the £5-a-day charge has become just another expense.
So last October the mayor felt confident enough to say he would base his bid for re-election on plans to extend the zone westwards.
On Monday, 3.3 million households, 250,000 businesses and 1,400 other bodies received a leaflet outlining Transport for London's (TfL) plans.
The mayor wants to see the zone double in size, to take in most of Westminster and the borough of Kensington and Chelsea, and says it could be in place by 2006.
The new boundary would stop just short of Shepherd's Bush to the west, run as far north as Kensal Green Cemetery and down to Chelsea Embankment in the south.
But the mayor faces several hurdles - not least securing government funding and determining whether the firm running the scheme, Capita, is up to the job.
Last year it was penalised £1m for poor performance, although TfL has said it has met all the performance targets since laid out for it.
And as before, Mr Livingstone faces stiff opposition - not so much from the motoring lobby, but from within Kensington and Chelsea.
The zone extension would cover a much more residential area; about 230,000 residents compared to the 150,000 people living in the current zone.
TfL's survey of Kensington and Chelsea last July suggested 53% of people in the borough wanted the charge in their area.
But this is disputed by some residents and the council, which says the plans split the borough, leaving 20,000 residents outside the zone.
Its survey found 61% of the 1,800 people surveyed gave a "flat no" to any kind of extension and only 2.5% supported the current extension scheme.
The West London Residents' Association, formed in the wake of the first news reports about the scheme, has been steadily growing.
Chairman Gordon Taylor, 75, told BBC News Online: "We started as the Chelsea Residents' Association but after the first meeting in November I was beset by people from Westminster, Belgravia and Fulham, so we had to change our name.
"We have about 5,500 members at the moment and they are joining at about 40 to 100 a day."
The group is gearing up for a fight, despite the mayor's comment last month that extending the zone was only a "medium priority", behind Crossrail and other projects.
It has distributed 75,000 leaflets and delivered another 25,000 by hand, carried out its own studies, written to newspapers and Mr Taylor has been up before the Greater London Authority (GLA).
"It's a full time job," said Mr Taylor.
Areas covered by the extension
Royal Albert Hall
"As soon as I read about the plans I did some calculations and saw it was just nonsense.
"I have lived here for 44 years in Kensington and in Chelsea - our borough's essentially a residential area and we have no congestion in the residential streets.
"The mayor has already admitted there is no economic case for it and no improvement in air quality - it's just pure politics."
Other changes mooted have included a £5 charge to drive to Heathrow or using satellite-based technology to monitor any area within the M25 London Orbital.
But TfL says there are "no plans to extend the charge zone any further than the western extension at the moment".
The extension would only take place after TfL has assessed two years of the current scheme's performance and if Mr Livingstone wins this year's mayoral elections.
The mayor is also awaiting the outcome of the Government Spending Review before he can work out how much he has to spend on his transport policies.
He has said there is no "financial case" for an extension to the zone - which is expected to bring in £10m a year but would cost about £100m to set up.
But he said the remaining part of Westminster and the affected part of Kensington and Chelsea were "pressing cases" for the charge's economic and financial benefits.
The public is being asked for its views on the current scheme over the next 10 weeks.
Congestion charge director Michele Dix said: "Although there are some concerns, it is the very purpose of this consultation to listen to them and to devise a scheme that would benefit all."