Has London's congestion charge worked?
The biggest congestion charge scheme to launch in any city got off to a smooth start on the morning of 17 February 2003, much to the surprise of London's then mayor Ken Livingstone.
A decade on he readily admits it was the only thing in his entire political career that "turned out better than I expected".
Motorists travelling into central London on that Monday morning faced the new £5 daily charge, and by the afternoon 57,000 had paid it.
The RAC reported there was not the anticipated early rush of drivers trying to get across the eight-square mile zone before 7am - the time the charge came in.
Mr Livingstone said: "What was amazing was nothing went wrong.
"We'd expected we'd have quite a few bits of congestion on the periphery, but we couldn't find a single point where the traffic didn't flow.
"The only real problem we had were the buses were all running so ahead of schedule they had to wait at the bus stop for a couple minutes."
At the time officials from 30 other British cities were reported to be considering introducing congestion charges if London's scheme was successful.
That never happened and, further afield, the only cities to adopt a similar scheme since are Milan and Stockholm.
Mr Livingstone believes there are two reasons: political cowardice and "modern" cities built after the introduction of the car that do not need a congestion charge.
He said: "If it wasn't for the Republicans, who control the New York State Assembly, Manhattan island would have one. Mayor Bloomberg really wants to do it but he can't get the votes.
"In Manchester the politicians were so nervous they said: 'we'll have a referendum first'.
"If I'd had a referendum first, with all the hysteria in the newspapers - I had two and a half years of newspapers saying it would be a disaster - you'd never have got it through. It was all doom and gloom.
"Political cowardice is always going to be a problem: people think they might lose votes if they do it - but very few cities actually need it."
Mr Livingstone now sees pollution as London's biggest challenge.
"We've all woken up to the fact that in London over 4,000 people die prematurely every year because of the air quality - that's worse than 9/11," he said.
"We're not just talking about a few elderly people dying a few months early. On average they're dying 11 years early.
"We've got to tackle it - that's the low-emission zone and Boris [Johnson] should be pressing ahead very rapidly and tightening up on diesel vehicles."
Although he scrapped the scheme's western extension zone when he succeeded Mr Livingstone in 2010, Mr Johnson has described the original scheme as a success which had benefited London.
On Wednesday he announced his vision to see the world's first "Ultra Low Emission Zone", meaning by 2020 only zero or low-emission cars would be allowed into central London. Time will tell if the argument for what seems a radical change can be won.
And although the congestion charge - which was also seen as a radical step a decade ago - has won over many of the original doubters, there are still those who claim it has not been a success.
According to TfL figures, traffic levels over the past 10 years have gone down by 10.2% but journey times for drivers have remained flat since 2007.
Barry Neil, whose east London-based company Ambient Computer Services travels into central London daily delivering computer equipment, claims this is evidence the congestion charge has failed.
He said: "We said when it launched it wasn't going to make any difference and unfortunately it hasn't.
"If it made it easier to drive through London, then great. But it doesn't. The jams are just as bad and it costs us £5,000 a year."
However, Elliot Jacobs, managing director of office supplies firm UOE, disagrees.
"Getting deliveries on time is really important and the congestion charge means we have a consistency of traffic flow and a reliability that we know where the traffic's going to be, and that's important.
"It means we can get there on time and that's worth £10 every day."