In New Jersey, drivers can get a learner's permit at age 16, an intermediate license at 17, and full licensure at age 18.
The decal law requires intermediate drivers to place a small red sticker on the front and back license plates of any vehicle they operate so police can see that the driver lacks a full-privilege license.
Intermediate drivers are limited to one passenger unless accompanied by an adult.
New Jersey has one of the most comprehensive, graduated licensing laws in the United States and already boasts a low teen crash-fatality rate. So the improvement in crashes is especially significant, Curry wrote.
The decal law was implemented after Kyleigh's Law became effective in May 2010. The law is named for Kyleigh D'Allesio and Tanner Birch, who were killed in 2006 by an intermediate driver carrying more than the allowed number of passengers.
Revisions added after the law's passage also made curfew 11:01 p.m. instead of midnight, among other changes.
In their study, Children's researchers reviewed the rate of police-reported crashes for teen drivers and noted the kind of license involved in each case. They compared monthly crash rates for about two years before the law went live on May 1, 2010, to the 13 months afterward.
Overall, accidents decreased by 9 percent post-law. The rate of crashes after midnight fell by 13 percent and multiple-vehicle crashes dropped by 8 percent.
Related citation rates also rose 14 percent.
Although most states have graduated licensing laws that phase teenagers into licensure, New Jersey is the only state to require decals for intermediate drivers.
The decals are "designed to support police" and "stop teens from not obeying these important safety laws," said Curry. Many other countries, such as Australia and Canada, are using decals for young drivers. But these have never been evaluated, she said.
The red decals have been controversial. It "marks [youth] with a scarlet letter for criminals and police," said Jeffrey Nadel, president of the National Youth Rights Association, an advocacy group in Washington. Instead of the decals, Nadel said, authorities should make the driving test harder.
Parents and some police officers have also expressed concern that the program could lead to law enforcement profiling teenagers.
But there haven't been cases or numbers showing that young drivers are being singled out by predators or the police, Curry said.
"The risk of teens being killed in an accident are greater than [their] being targeted," she said.
Gillian Francella can be reached at firstname.lastname@example.org.