Parents driving to school are increasing congestion

But the motoring organisation RAC, which carried out the research, said the dangers had been overestimated, with fewer pupils dying on roads each year.

It found 54% of parents who took pupils in by car did so because of concerns over safety.

A further 32% thought it was quicker to drive their children than consider other modes of transport.

'Walking bus'

The findings come as 12,000 UK schools are taking part in International Walk to School Week.

To celebrate this, pupils in Kingston, Surrey, will attempt to create a world record for the longest "walking bus" on Wednesday, with up to 1,000 going to school in unison.

The RAC is warning, however, that the complex issue of the school run cannot be solved by simply holding an "awareness week".

It called for more "practical schemes" to ensure more children continue walking to school, improving their fitness and reducing road congestion.

Overweight and unfit

RAC spokeswoman Rebecca Bell said: "Road casualty figures released last week indicate that fewer children than ever are being killed or injured on foot or on their bikes.

"We think this is because far fewer children are now walking or cycling to school than ever before.

"The car is king and that's not simply due to convenience. Parents are rightly worried about the safety of their children if they are left to travel to school independently.

"Clearly, this is a problem which is adding to the inexorable rise of congestion on our roads and is one reason why school-aged children are increasingly overweight and unfit."

Walk to School Week follows Education Secretary Charles Clarke's announcement last week of a �50m investment to tackle the problems caused by the school run.

Ms Bell added: "It is practical schemes, combined with serious investment into public transport systems, that will address the problem effectively."

Jo Pike, National Walk to School campaign coordinator, said there were "undeniable benefits" from walking to school.

Pupils' safety was central, with road safety resources sent to schools, and road safety officers being consulted throughout the planning and implementation of the campaign.

Parked cars

Parents or other carers were asked to walk with young children, while pupils old enough to walk without an adult were still encouraged to do so in groups.

"One of the primary reasons parents drive their children to school is to protect them from the danger of traffic and yet by doing so, more dangers are being created at the school gate," she said.

"Cars are parked as close to the entrance as possible, regardless of the Keep Clear markings, with the engines left running.

"Pupils are left to cross the road between these cars making it difficult for them to see the oncoming traffic, whilst drivers hurry to get home, actually causing more dangers on the road outside the school as a direct result of more cars on the school run."

Robert Smith, Dorset County Council's road safety team leader and chair of the International Walk To School co-ordinating committee was particularly concerned about the dangers caused outside schools at the end of the school day.

"It's incredible to think that some parents, who cite "lack of time" as their reason for using the car, will arrive 45-50 minutes before the end of the school day to grab the best parking space for a quick getaway," he said.

"If they do this every school day afternoon, as many do, they will clock up an astonishing 160 hours or almost a whole week just sitting, waiting in their cars, in the space of a year."

Surely they could walk occasionally, he added.