Just 40 percent of children aged 4 to 8 use car safety seats or booster seats at least occasionally - meaning that most children risk being thrown from the car in the case of an accident, according to a study released on Tuesday.

The study, published in the Annals of Emergency Medicine, shows that many people driving children do not have booster seats, and feel the risk is acceptable because they are making only short trips.

“Emergency physicians cringe when we see a child riding unrestrained in a vehicle because we know if it crashes, the child will be hurled like a missile,” Dr. Herbert Garrison of East Carolina University in Greenville, North Carolina, wrote in a commentary on the survey.

“The result for the child may be severe injury or death.”

For the survey, the National Highway Traffic Safety Administration interviewed 6,000 randomly chosen Americans over the age of 16 in 2003, asking questions about safety belts, child safety seats, air bag crash injuries and other issues.

The survey found that 21 percent of children aged 4 to 8 rode in a booster seat even occasionally, while another 19 percent rode in a front-facing child safety seat at least on occasion.

State laws vary on when and how children should be in safety seats but children up to about 40 pounds should ride in child safety seats.

After that, experts recommend booster seats to make sure smaller children fit properly into safety belts.

Half the parents and caregivers who put the child into a booster seat only occasionally said the child was only in the vehicle a very short time. Another 41 percent said no seat was available and 34 percent said the child did not like the seat, the NHTSA survey found.

Motor vehicle crashes are the most common cause of childhood death in the United States.

“Children ages 4 to 7 who ride in booster seats are 59 percent less likely to be injured in a crash than children restrained by only a safety belt,” Garrison wrote.