Engineer Jens Bovenkerk's goal is to improve pedestrian safety. His research has taught him that even for pedestrians, an airbag is one of the most effective ways of avoiding fatalities.

"An airbag could be fitted externally between the bonnet and the windshield and would be released on impact were there a collision between a car and a pedestrian," he said.

The airbag would be triggered by sensors in the bumper of the car. As with a standard airbag, it would inflate in less than a tenth of a second by the equivalent of a solid rocket booster.

In a similar process, sodium azide and potassium nitrate would react rapidly to produce a large pulse of hot nitrogen gas. This inflates the bag, which literally bursts out of its position as it expands. Stored between the hood and the windshield, it would be able to halt a human body before the head had time to hit the window.

Perfecting the prototype

In the initial stages of development, the main problem was that the airbag covered the entire windshield, reducing the driver's visibility. But scientists have now designed prototypes with small holes which allow the motorist to see out.

Japanese automobile maker Toyota has already perfected a model, although other manufacturers have remained skeptical -- not least because of the costs. A cheaper alternative is what's known as an "active hood system," which automatically raises the automobile hood in the event of pedestrian impact.

But traffic experts say that this type of buffer zone does not go far enough. Over 80 percent of the people who lose their lives in traffic accidents every year die from injuries sustained by hitting a windshield. What usually happen is that when they hit the bumper then lose their footing, their upper body is spun into the air and hits the hood, while the head impacts against the windshield.

Jens Bovenkerk said he is confident that the airbag is the most promising way of reducing traffic fatalities, even though he admits it has its flaws. Clearly, it does not help pedestrians flung against asphalt.

"Pedestrians will always be the most vulnerable," he said. "All we can do is try to minimize traffic fatalities by a certain percentage."

In fact, this percentage is surprisingly high. Experts estimate that an airbag for pedestrians could cut back the incidence of head injuries by 90 percent as well as halving the number of injuries to the upper body.

Manufacturers put brakes on safety

However, the major car makers are unlikely ever to introduce pedestrian safety precautions voluntarily.

"A number of car makers might refer to the issue of pedestrian safety in their publicity material, but they're put off by the expense," Bovenkerk said. "What we need are laws which make it compulsory for manufacturers to fit these new features."

The EU is already taking action and has set itself an ambitious target: it plans to half the number of traffic-related deaths by 2010. At the moment, some 4,600 pedestrians in Europe die in traffic accidents every year.

The first phase of the EU's pedestrian safety directive was introduced in October 2005. This required new vehicles to have larger and lower bumpers which are better able to absorb the force of an impact. And now, experts predict that it won't be long before pedestrian airbags catch on -- they expect them to have been made compulsory by 2008.