The national Governor’s Highway Safety Association is recommending that all states extend junior driving restrictions until age 21.

In a study released Wednesday, the association said there was a 10 percent increase in 2015 in fatal traffic accidents for teenage drivers, the first increase since 2006. With the number of fatal accidents involving drivers between 18 and 20 years old higher than those involving younger drivers, the association recommends including older teenagers in the restricted group that requires more extensive training before they can obtain a full license.

The 38-page study, “Mission Not Accomplished: Teen Safe Driving, the Next Chapter,” said teen drivers were involved in 4,689 fatal accidents last year, up from 4,272 in 2014. While fatal accidents involving teen drivers were down over a 10-year period, the decline was 51 percent for younger teens but only 40 percent for older teens.

To Pam Fischer, a New Jersey consultant who wrote the study, that indicates some young drivers may not be getting the amount of training they should. That’s why she recommended extending the graduated licensing requirement to age 21 in all states instead of 18, where it is everywhere except New Jersey, which has the graduated license for every new driver regardless of age.

“(Age limits) are just numbers,” said Fischer. “When you look at a teenager, we know scientifically they don’t have the maturity, the insight, the fully developed brain to make safe decisions.

“When we allow them to get a license with no restrictions, we’re really doing them a disservice and we’re not looking at the scientific evidence.”

Details on graduated license requirements vary from state to state, but in Pennsylvania teens can receive a learner’s permit at age 16. After six months, they can get a junior license if they complete 65 hours of driving, including 10 hours of night driving and five hours in inclement weather, and pass written and on-road exams.

The junior license prevents them from driving between 11 p.m. and 5 a.m. and limits the number of passengers they can have in the vehicle. If they complete a year with no accidents or traffic violations, they can get a full license.

But in Pennsylvania and most other states, none of those steps is required if they apply for a learner’s permit at age 18. That means at age 18, if a driver can pass the test, they can receive a full license regardless of how much training they have received.

The recommendation from the Governors Association encourages all states to adopt the graduated license procedure through at least age 21.

Part of the reason the number of fatalities has increased is because the number of drivers is on the rise again after dropping off during the economic recession, Fischer said. But she says only one reason.

“We know GDL is working for young kids, but we can see by looking at the numbers that older teenagers just aren’t ready (for a full license) if they haven’t had the training,” she said. “If the GDL standards are extended to that group, they’re going to see a similar trend and safer drivers.”

Tim Rogers, who as president of the Rogers Driving School in Ross, Pa., is involved in training 700 to 800 drivers a year, said he would support extending junior licenses to older teens.

“If the state sees a need for 65 hours of driving before a 16-year-old can get a license, I’m not sure why that goes away with age,” he said.