The family of crash test dummies has grown this year with the addition of a youngster who is just about the size at which kids graduate from a booster seat to a seat belt.

The unhappy life of this dummy, modeled after a 10-year-old, will be spent evaluating the effectiveness of child seats and boosters for children weighing more than 65 pounds.

Child auto safety requirements are set by states, which have a wide variety of standards that use height, weight and age to determine when a child is ready to use a seat belt. The average age threshold is 6 to 8, if children are tall enough and weigh enough. South Carolina, often an outlier, allows seat belt use by 1-year-olds if they weigh more than 80 pounds.

“Our new dummy is an excellent addition to NHTSA’s extensive child seat compliance testing program and will enable the agency to gather the best data yet on the performance of higher-weight child seats,” said David Strickland, director of the National Highway Traffic Safety Administration.

NHTSA, which issued a final rule on child seats Tuesday, says 1,314 children ages 14 years and younger were killed in crashes in 2009, and about 179,000 were injured. The agency said safety seats in passenger cars reduce the risk of death by 71 percent for infants and 54 percent for children up to age 4.

Guidelines from the federal Centers for Disease Control and Prevention recommend a rear-facing seat secured in the back seat for children less than a year old and weighing less than 20 pounds. After that, until children are 4 and weigh 40 pounds, they should be in a forward-facing seat in the back seat. Until they turn 8 or grow taller than 4 feet 9 inches, they should ride in booster seats in the back seat. When they outgrow them, they should be belted in the back seat until age 13.

“The new test dummy breaks new ground for the department’s crash test program and is a significant step forward for evaluating child seat performance.” said U.S. Transportation Secretary Ray LaHood.

The CDC found that more than 618,000 children 12 and younger rode without a safety or booster seat or a seat belt some of the time during a one-year period.

The childhood obesity epidemic has created a growing number of children over 65 pounds, and car seat manufacturers have responded with products for them. Federal regulators who set standards for car seats have been hindered in testing the new seats because they lacked an appropriate dummy. The NHTSA rule issued Tuesday covers safety standards for car and booster seats for children weighing betweem 65 and 80 pounds. Manufacturers will have two years to certify their higher-weight car seats and boosters to meet the new requirements.

A federal law passed in 2002 required development of a new dummy within two years, but the effort had been stymied by a lack of funding for the research needed.

The 10-year-old child dummy joins the family of test dummies used to evaluate child restraint systems: a newborn, a 12-month-old, a 3-year-old, a 6-year-old and a weighted 6-year-old.