New NHTSA/Johns Hopkins Report on Effectiveness of GDL Components

NHTSA released a new teen driving report today showing that comprehensive Graduated Drivers Licensing systems can reduce fatalities among 16-year-old drivers by about 20 percent.

The report looked at the involvement of 16-year-old drivers in fatal crashes nationwide, between 1994 and 2004, to assess the impacts of various combinations of seven key components of state GDL systems. The study found that 16-year-old drivers in states with GDL systems that included 6 or 7 of these components had fatal crash rates 21 percent lower than those without any of these components. Sixteen-year-old drivers in states with 5 of these components had 18 percent lower fatal crash rates. The combination of components shown to have the greatest reduction in fatal crash rates was:

Minimum age requirements for three stages of licensure (learner’s, intermediate, full license);
Three or more month mandatory “hold” before advancing from learner’s permit to intermediate license;
Nighttime driving restriction; and
Either a passenger restriction OR required supervised driving of at least 30 hours.

It’s worth noting that the report was less stringent (compared to AAA’s GDL guidelines, listed below in italics) in its requirements for each of the components. The report used:

Minimum age for learner’s permit of 15 ½. AAA calls for age 16.
Mandatory waiting period of at least 3 months. AAA calls for 6 months.
Minimum if 30 hours of supervised driving. AAA calls for 50 hours, including 10 at night.
Minimum age for intermediate license of 16. AAA calls for 16 ½.
Any nighttime restriction. AAA calls for a minimum of midnight to 5 a.m.
Any passenger restriction. AAA calls for no passengers during first six months.
Minimum age for full licensure of 17. AAA calls for 18.

The way the components were scored, a state with any night restriction on the books was counted as having a night restriction, grouping those that began at 9 p.m. with those that began at 1 a.m. These simplifications were necessary to allow the researchers sufficient sample size to conduct their analysis. States with more comprehensive GDL systems (both the actual limits and enforcement/compliance with them), yield greater safety benefits.

The research does not assess individual state GDL systems or ascribe percent improvements to individual components of GDL. Five states (ME, NH, RI, UT, VA) were excluded from the sample because they changed their GDL more than twice during the study period (1994-2004) researchers analyzed.

View the full report