The 6.5mph C-charge zone

An Evening Standard survey has found evidence that traffic on 12 key routes through central London travels at an average of only 6.5 mph. Speeds on some main routes are now slower than a walking pace. On the Strand - a vital east-west corridor - the average speed is 1.8 mph.

The Standard's survey, which was conducted in association with the Institute of Advanced Motorists, raises serious questions over the C-charge zone.

It comes a day after Ken Livingstone unveiled plans to increase the amount drivers of gas-guzzlers will pay to enter the zone from £8 a day to £25 and transport commissioner Peter Hendy claimed traffic jams had fallen by a quarter.

Our survey, which was overseen by Kevin Delaney, former head of the Met's traffic division, found:

The average speed on roads we tested in the "old" charging zone, including its ring road, is now only 5.7 mph.

In the western extension zone, introduced last February, the average speed is 7.45mph - lower than the average of 11.1mph recorded in autumn 2006.

The fastest route is the western zone ring road with an average speed of nearly 12mph.

Speeds have dropped in the past two years across the whole zone, down from an average of 9.9 mph in February 2006 to 6.5mph now.

Mr Delaney, head of road safety for the institute's motoring trust, said: "The results of the survey are very disappointing. They fall a long way short of the promises made when the scheme was introduced and are a great deal worse than early results.

"It must be a disappointment to the Mayor and perhaps is something other local authorities and the Government might want to take account of before it is extended to other cities."

Mr Delaney said most of the blame appeared to lie with the re-phasing of traffic lights - with motorists held on red for longer - and the loss of road space through junction alterations and widened pavements. Bendy buses also created extra congestion, he added.

Claims that a proliferation of roadworks is causing the delays appear to be unfounded. In our survey, we encountered only one set in the "old" charging zone and one on the boundary road of the western extension zone - fewer than for some previous surveys.

In February 2002, Transport for London announced that the average traffic speed in central London had fallen to

9.9mph - slower than the speed of a horse and carriage. Asked if it was concerned that speeds were now lower, a TfL spokesman said: "The point to remember is that congestion charging has successfully reduced traffic in the original zone by 21 per cent - some 70,000 cars every day - and has prevented London from grinding to a halt."

Traffic levels were continuing "to stay well below pre-charging levels".

The spokesman continued: "We have recognised that traffic speeds have begun to slow. In central London road space is being squeezed by the huge increase in work being carried out by utility companies."

But Douglas McWilliams, chief executive of the Centre for Economics and Business Research, said recently much of the current congestion was caused by "more buses than there is space" for.

He said that bendy buses in particular were to blame - a claim denied by TfL. Mr McWilliams called for "road space removal" - for example, pavement widening - to be reversed.

Baroness Jo Valentine, chief executive of business lobbying group London First, said: "Congestion charging has been a success story for the Mayor, with 70,000 fewer vehicles entering the zone daily, but business is concerned that traffic speeds are plummeting. Congestion is back to its worst.

"We call on the Mayor to sort out the problems in central London caused by roadworks and endless bus jams . The Mayoral candidate who wins business's support will be the one who shows leadership in tackling congestion and the pollution it causes, championing fresh solutions to this critical problem."

We surveyed the same 12 routes on each occasion - all typical commuter/delivery routes ranging from half a mile to three miles, in addition to the inner ring road. Each was driven at the legal speed limit where possible and timed and measured.