In a series of secret town hall meetings, John Whitelegg, a Lancaster Green, was able to turn the countys Tory transport chief to implement Green Party policy on speed limits. The fact that John is also Professor of Sustainable Transport at Liverpool John Moores University helped make him more palatable to the Conservative Tim Ashton.

Ashton took the transport cabinet post in 2009 after a blue tide ousted Labour from power in Lancashire. In that same election, the Greens Sam Riches won a county council seat and she spearheaded the public side of the 20mph campaign, holding public meetings, garnering support with door- to-door surveys during election times and highlighting the risk to school children in her division.

John had found the previous Labour regime obnoxiously unhelpful when he first began trying to persuade Lancashire to adopt countywide 20mph limits 11 years ago. They hated the fact I was Green Party. Greens were taking their votes.

But Ashton was more receptive. Eventually, the Tory road supremo was calling John Whitelegg for advice on overcoming the hurdles placed by his officers. He also had to battle his own backbenchers who believed 20mph would slow journey time.

John got all the directors of public health in the North West to write personally to Tim Ashton at his home urging him that cutting the speed limit to 20mph would be the single biggest improvement he could make to health in Lancashire.

The biggest boost came in August 2010 when national and local newspapers cited a report revealing the Lancashire districts of Preston, Burnley and Morecombe as the worst in the country for road injury to children. It seemed to act as a wake-up call to Tim Ashton, who has direct responsibility for bringing down road injuries in Lancashire.

It was a perfect storm of events, said Riches.

Things came to a head when Riches resisted a council plan to put a short 20mph limit on a stretch of road in her division, near a dangerous school crossing, saying it would make matters worse. Summoned to a meeting with Tim Ashton, he asked her to explain why she was blocking the move. Then he said: Would you support an area-wide 20mph limit?

Shortly afterwards, the policy initiative was announced. Now half-way through the three-year, £9.4 million programme, average speeds are down in some areas but are unchanged in others and the perception is that more enforcement and publicity is needed.

A series of high-profile police speed gun checks is imminent, followed by a countywide poster, radio and new media publicity campaign. Paul Binks, Lancashires Road and Transport Safety Manager said: We are hoping that it will become socially unacceptable to drive at more than 20mph.

Its about changing the culture, said Whitelegg. For Riches, the campaign illustrates an uncomfortable and often forgotten truth: Green councillors can only change policy if they persuade the opposition as well.

Robert Lindsay is a Green Party member in Suffolk.

Some facts about Total 20, or area wide 20mph limits

Total 20 avoids the use of expensive humps or other physical calming measures. The idea is that by imposing 20 limits over a wide area such as a town, city, borough or county, drivers get the message that it is unacceptable to drive at more than 20mph in a residential area.

Total 20 areas cost just £333 per road and are very cost effective. The Government calculates the cost of a road death to the economy at £1.8 million. Portsmouths Total 20 scheme cut serious injuries and deaths by 22%.

If you are driving at 30mph and someone runs out three cars lengths in front of you, you will hit them at 27mph. The impact on that person is equivalent to falling from the third floor of a building. At 20mph you will stop just in time.

20mph areas lengthen the average car journey by just 30 seconds.

Britains Department for Transport sets national targets to reduce road deaths and casualties by a certain percentage over a certain time, implying it finds a certain level of road death acceptable. Sweden has a zero tolerance for road death policy which has energised road safety professionals and led to widespread 20mph limits.