Four-wheel drives - or 4x4s - should carry health warnings to raise awareness of the increased risk to pedestrians compared with ordinary cars, according to researchers from the Trinity College Dublin (TCD).

The researchers believe that this should form part of an integrated approach from public health, transportation and road safety agencies to address this growing threat.

Among road users, pedestrians are already a group at high risk, and older people are particularly vulnerable, according to authors Prof. Desmond O'Neill, an expert in the field of Ageing and Transportation and Dr. Ciaran Simms, an expert in Crash Impact Bioengineering at TCD's Centre for Bioengineering.

People over 60 are more than four times as likely to die if injured by a car than younger people, say the researchers.

In Europe sales of 4x4s, also called sports utility vehicles (SUVs), have increased by 15 per cent in the past year, while sales of standard cars have dropped by 4 per cent.

A recent US study found that, for the same collision speed, the likelihood of a pedestrian fatality is nearly doubled in the event of a collision with a large SUV compared with a passenger car. Other studies report higher rates (up to four times) of severe injury and death.

The increased risk from SUVs arises primarily from the geometry of the front end structure, explain the authors. Pedestrian injuries from cars are mainly leg fractures and knee injuries from the primary impact with the bumper and head injuries from the secondary impact with the bonnet or windscreen.

Dr. Ciaran Simms: "I am in favour of introducing a vehicle registration tax which is calculated based in part on the vehicle's overall safety rating."

But because SUV bonnets are higher than those of cars, this results in more severe primary impact on the critical central body regions of the upper leg and pelvis, and a doubling of injuries to vulnerable regions such as the head, thorax, and abdomen.

"The evidence clearly shows that SUVs represent a significantly greater hazard to pedestrians than ordinary cars - and those pedestrians are getting older and more vulnerable", said Prof. O'Neill.

"Measures to address this threat should include changing crash investigation processes to identify SUVs in vehicle-pedestrian impact statistics, and displaying warning notices on SUVs to help inform consumers of the increased risks", he added.

Although the occupants of an SUV have some more protection in a crash, they inflict proportionately more damage on other road users/drivers, so the overall balance of the equation is negative and should be a cause of concern for society, argue the authors.

Addressing the hazards posed by SUVs to pedestrians is an emerging and real traffic safety challenge in the developed world, they conclude.

"I am in favour of introducing a vehicle registration tax which is calculated based in part on the vehicle's overall safety rating", said Dr. Simms.

The findings are published in the British Medical Journal.