Passengers are no safer riding in a 4x4 than an ordinary car, because the risk of rolling over in an 4x4 cancels out the safety advantages of their greater size and weight, according to the study. Researchers said that the findings dispel the myth that has helped to fuel the growing popularity of 4x4s. Dennis Durbin, a co-author of the study at the Children’s Hospital of Philadelphia, said: “We are not saying they’re worse. We’re challenging the conventional wisdom that everyone assumed they were better.”

The study found that the extra weight of 4x4s reduced the risk of injury by more than a third. But that was offset by the discovery that 4x4s were more than twice as likely as cars to roll over in crashes.

Children in rollovers were three times more likely to be seriously injured than in non-rollovers. Another strong risk factor for young children was from an air bag deploying while they rode in the front. Researchers said that they should travel in the back.