At 8.50am in term time, one in five cars on urban roads is taking children to school. In the past decade, the proportion of car journeys to school has risen from 16 per cent to 29 per cent.
But very few children are driven to Wheatfields junior school. "We have reduced numbers coming by car", says headteacher Carol Laws. "Fifty per cent used to - now it's less than 20 per cent."
The walking bus - groups of children walking on a regular route with parent "drivers" and "conductors" - was conceived at Carol Laws' school. It began with a child's chance remark: why can't lots of children walk to school with a mum? A jolly good idea, but how do you get something like this started?
"You really do need someone in school to be in overall charge", says Mrs Laws. "This has been successful because I know the parents - who to ask. If one co-ordinator rings me with a problem, I can soon get it sorted."
Wheatfields School, on the outskirts of St Albans in Hertfordshire, is at the end of a narrow cul- de-sac. At drop-off and pick-up times, the school entrance was regularly becoming clogged with cars and the air heavy with exhaust fumes.
To plan the walking bus, a steering committee was set up, and it held meetings with road safety officials and the police.
The road safety officials took the volunteer bus drivers along the route, looking at the safest places to cross, pointing out potential hazards.
Drivers are trained for a specific route and, like train drivers, they cannot drive a bus on another route until they have been trained for it. The police are also involved to ensure that all the drivers have a "clean record".
There are four walking buses at Wheatfields and each has an adult co-ordinator who ensures that there is always a driver and a conductor.
The bus driver has a register. The parent helpers include dads who fit in "driving" with their shift work. Those staffing each bus wear colour-coded waistcoats - each bus has its own colour - and each homeward bound bus meets in its own corner of the playground. If a child is staying for an evening club, they have to let the bus driver know.
Children are dropped off at a stop near their homes, and an adult is expected to come and collect them. If the parent cannot be there, then they must send a letter to school - the same procedure also applies to the mornng routine. The drivers are covered by the local authority's public liability insurance.
Parents who are not near one of the bus routes have told Carol Laws that their children are so eager to join in that they pester parents to drop them off at a friend's or their grandma's house because they are on the route.
Some of the walking buses are complete with trolleys to carry satchels and PE bags, which have been provided by the local Homebase superstore.
Once the scheme was up and running - or walking - Carol Laws was keen to introduce a reward scheme to ensure it did not lose impetus. Children are given a sticker each time they use the bus which can be collected and exchanged for books in the school shop.
Mrs Laws will reward children who walk or cycle to school as a formal "Well done", but makes no effort to criticise those parents who bring their children by car.
But she does not hesitate to ring the police if the few parents who still use cars are parking dangerously. The police soon respond.
To help emphasise the feeling of unity, the bus drivers and conductors are always included in "green" assemblies and publicity events. Last summer Carol Laws was worried that those parents whose children were in Year 6 would not be replaced. But, happily, her fears were not realised.
Back behind the "steering wheel", the scheme appears to be working well. "Timing is important," says Katie Telkman, one of the bus drivers. "In the morning, we wait two minutes at each stop and then we go - we can't hang about.
"If I can't make it, I have to let the bus co-ordinator know as soon as possible so she can ring up one of the reserves."
Mrs Telkman says the walking bus has produced personal benefits. "People have said to me, 'Oh, you do look well!' I don't drive the bus every day so, on my days off when someone else is walking my child to school, I really enjoy that free time."
The children talk to each other as they walk - they are getting to know boys and girls in other year groups and travelling numbers are not affected by the weather.
One mum said: "When I missed the walking bus, I had to get him there in the car. I felt so ashamedI we didn't ever miss it again!" Notes: Guidelines on setting up a walking bus, including sample letters and consent forms, are available from Hertfordshire County Council, priced pound;5 or free to Herts schools. Tel: 01727 816962.Walk to School packs, also pound;5, are available from the The Pedestrians Association on 020 7820 1010.