Role of Supervised

Driving Requirements

In a Graduated Driver

Licensing Program

The
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in the interest of information exchange. The opinions, findings 

and conclusions expressed in this publication are those of 

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Suggested APA Format for This Document Reference:

Foss, R. D., Masten, S. V., Goodwin, A. H., & O’Brien, N. P. (2012, March). The role of supervised 

driving requirements in graduated driver licensing programs. (Report No. DOT HS 811 550.) 

Washington, DC: National Highway Traffic Safety Administration.
i 

Technical Report Documentation Page

1. Report No.

DOT HS 811 550

2. Government Accession No. 3. Recipients' Catalog No.

4. Title and Subtitle

The Role of Supervised Driving Requirements in 

Graduated Driver Licensing Programs

5. Report Date

 March 2012 

6. Performing Organization Code NTI-132

7. Authors: 

Robert D. Foss, Scott V. Masten, 

Arthur H. Goodwin, Natalie P. O’Brien

8. Performing Organization Report No.

9. Performing Organization Name and Address

Highway Safety Research Center 

University of North Carolina 

730 Martin Luther King, Jr., Blvd., Suite 300

Chapel Hill, NC 27599-3430

TransAnalytics, LLC

336 West Broad Street

Quakertown, PA 18951

10. Work Unit No. (TRAIS)n code

11. Contract of Grant No.

DTNH22-05-D-05043, Task Order 09

12. Sponsoring Agency Name and Address

National Highway Traffic Safety Administration

U.S. Department of Transportation

Office of Behavioral Safety Research, NTI-130

1200 New Jersey Avenue SE. 

Washington, DC 20590

13. Type of Report and Period Covered

NHTSA Technical Report

14. Sponsoring Agency Code

15.Supplementary Notes

16. Abstract

Many States require parents to certify that their teens have completed a certain amount of supervised driving practice, usually 40 to 50 hours, 

before they are permitted to obtain an intermediate license. Although strongly supported by numerous groups and organizations, the effectiveness 

of supervised practice requirements is unknown. NHTSA conducted a cross-sectional comparison of fatal crash rates throughout the United 

States, and examined State crash data using interrupted time-series analysis in a small number of States that had increased their required number 

of supervised driving hours. To supplement and provide insight into these findings, the University of North Carolina-Highway Safety Research 

Center conducted telephone interviews, funded by State Farm Insurance, with parents of newly licensed teenage drivers in 5 States (Maryland, 

Minnesota, Ohio, South Carolina, and Washington) with varying supervised driving requirements. Employees of licensing bureaus in these States 

were also contacted by telephone to determine how they conveyed the requirements to parents and teenagers. 

Analyses of the Fatality Analysis Reporting System (FARS) showed that fatal-crash rates of 16- and 17- year-olds did not differ across States with 

varying supervised driving requirements. Crash analyses in Minnesota, the only State to change the number of required practice hours without 

changing other Graduated Driver Licensing (GDL) components, did not find any difference in 16- and 17-year-old-driver fatal or serious injury 

crash rates following the change in the requirement. Interviews with parents and licensing officials showed that awareness of the supervised 

driving requirements was weak in all 5 States. Only 32% of parents overall (range 15% to 55%) could correctly identify the number of hours 

required by their State. Almost all parents in Maryland (91%) reported using a log provided by the licensing agency to keep track of their teens’ 

driving and about half of Maryland parents correctly reported the number of required supervised hours. With low parental awareness and little or 

no licensing agency verification, it is difficult to determine whether teenagers drove the minimum number of supervised hours required by their 

States. These findings suggest that improvements in communications with parents and novice drivers about supervised driving requirements, 

guidance to parents about the best techniques to provide supervision, and tracking actual hours and conditions of supervised driving would be 

beneficial. 

17. Key Words 

Teen Drivers, Graduated Driver Licensing, Parental 

Involvement, Supervised Driving, Teen Crash Rates

18. Distribution Statement

Document is available to the public from the National 

Technical Information Service www.ntis.gov

19. Security Classif. 

(of this report)

 Unclassified

20. Security Classif. 

(of this page)

 Unclassified

21. No of Pages

92 

22. Price
ii
iii

TABLE OF CONTENTS

Executive Summary .................................................................................................................... v 

Background............................................................................................................................... xii

Crash Analyses........................................................................................................................... 1 

Teenage Driver Fatal Crash Involvement – All U.S. Jurisdictions .......................................... 1 

 Data ................................................................................................................................ 1 

 Coding State GDL Components and Other Pertinent Traffic Laws................................... 1 

 Coding for Other Traffic Safety Laws............................................................................... 4 

 Analysis Method .............................................................................................................. 5 

 Results ............................................................................................................................ 7 

Effect of Changed Supervised Driving Requirements in Individual States ...........................10

 Selection of States.........................................................................................................10

 Data .............................................................................................................................. 12 

 Analysis Method ............................................................................................................ 13 

 Results .......................................................................................................................... 14 

 Minnesota................................................................................................................ 14 

 Illinois and South Carolina ...................................................................................... .18 

 Virginia and Pennsylvania....................................................................................... .22 

 Summary....................................................................................................................... 27 

Parent Interviews ...................................................................................................................... 28 

Structured Interviews........................................................................................................... 28 

 Respondent Characteristics...........................................................................................30

 Awareness of Supervised Hours Requirements.............................................................31

 Amount of Supervised Driving Practice Teens Obtain ...................................................36

 Perceptions of Enforcement of Supervised Driving Requirements by 

 Licensing Agencies........................................................................................................ 38 

 Approval of Supervised Driving Requirements...............................................................40

 Analysis by Length of Time to Complete Learner Stage Requirements ......................... 45 

Unstructured interviews....................................................................................................... 47 

 Respondent Characteristics...........................................................................................47

 What Parents Tried to Accomplish During the Learner Stage ........................................48

 Parents' Opinions Concerning Mandated Hours of Supervision.....................................48

 How Parents Decided When Their Teens Were Ready to Obtain a License..................49

 Feasibility of Completing Supervised Driving Requirements ..........................................50

 How Parents Learned About Supervised Practice Requirements ..................................50

 Parents' Understanding of the Rationale for Required Hours Practice........................... 51 

 How Parents Kept Track of Their Teens’ Driving Practice.............................................. 51 

 Overall Thoughts About Their Experience and Advice for Other Parents....................... 53 

Licensing Bureau Interviews................................................................................................ 54 

 Results ..........................................................................................................................54

Discussion and Conclusions ..................................................................................................... 56 

Crash Analyses ................................................................................................................... 56 

Parental Knowledge, Understanding, and Beliefs................................................................ 57 

Findings .............................................................................................................................. 58 

Study Limitations................................................................................................................. 62 

Needed Research ............................................................................................................... 64 

Conclusion .......................................................................................................................... 65 

References ............................................................................................................................... 66 

Appendix A ............................................................................................................................... 70 
iv

LIST OF TABLES AND FIGURES

Tables

Table 1: Minimum Required Hours of Supervised Driving ........................................................ xiii

Table 2: GDL Components Coded .............................................................................................. 3 

Table 3: Other Traffic Safety Laws Coded................................................................................... 4 

Table 4: Adjusted Incidence Rate Ratios for Driver Fatal Crash Involvements ............................ 8 

Table 5: States That Increased Their Hours of Supervised Driving ...........................................11

Table 6: Additional States Considered for Analyses..................................................................12

Table 7: Sudden-Permanent ARIMA Models for Fatal/Serious-Injury Crash Rates in 

 Minnesota ...........................................................................................................................15

Table 8: Sudden-Permanent ARIMA Models for Fatal/Serious-Injury Crash Rates in Virginia...23

Table 9: Sudden-Permanent ARIMA Models for Fatal/Serious-Injury Crash Rates in 

Pennsylvania.......................................................................................................................23

Table 10: Supervised Driving and Minimum Age Requirements in States Where Parents Were 

Interviewed..........................................................................................................................28

Table 11: Unstructured Interview Respondents’ Awareness of Supervised Driving 

 Requirement .......................................................................................................................48

Figures

Figure 1.a: Minnisota Fatal/Serious-Injury Crash Rates per 10,000 Population.........................16

Figure 1.b: Minnesota Fatal/Serious-Injury Crash Rates, 12 Month Moving Average ................17

Figure 2: Illinois Fatal/Serious-Injury Crash Rates per 10,000 Population ................................. 20

Figure 3: South Carolina Fatal/Serious-Injury Crash Rates per 10,000 Population....................21

Figure 4: Virginia Fatal/Serious-Injury Crash Rates per 10,000 Population ...............................25

Figure 5: Pennsylvania Fatal/Serious-Injury Crash Rates per 10,000 Population......................26

Figure 6: Parents Who Believe Supervised Driving Is Required ................................................31

Figure 7: Parents Who Know Correct Number Among Those Who Believe a Certain Number 

 Is Required..........................................................................................................................32

Figure 8: Parents Who Know Correct Number of Required Hours for Supervised Driving .........33

Figure 9: Parents Who Believe Supervised Driving Is Required at Night...................................34

Figure 10: Parents Who Know Correct Number of Required Hours for Supervised Driving 

at Night................................................................................................................................35

Figure 11: Parents Who Report Using a Written Record or Log ................................................36

Figure 12: Parents Who Report They Were Required to Keep a Log ........................................38

Figure 13: Parents Who Report They Were Required to Sign a Form.......................................39

Figure 14: Parents Who Approve of Requiring a Certain Number of Hours...............................40

Figure 15: Parents Who Approve of Requiring a Certain Number of Hours, by State ................41

Figure 16: Hours of Driving Experience Parents Believe are Needed Before Teens Are 

Ready to Drive Safely on Their Own ...................................................................................42

Figure 17: Hours of Driving Experience Parents Believe Are Needed Before Teens Are 

Ready to Drive Safely on Their Own, by State.....................................................................43

Figure 18: Parent Opinion of a 6-Month Requirement for the Learner Stage.............................44

Figure 19: Duration Teens Held Learner Permit by Period State Allows Between Minimum 

 Ages for Learner and Intermediate License.........................................................................46
v 

EXECUTIVE SUMMARY

All States in the United States have adopted graduated driver licensing (GDL) systems in an 

effort to reduce crashes and fatalities among young drivers. Traditional GDL systems include 

three licensing stages: initial learner stage, the intermediate or provisional stage, and full 

licensure. An important component of GDL is the extended learner stage for beginning drivers. 

This stage is designed to ensure that a novice driver gains valuable driving experience under 

the supervision of an experienced adult driver. Despite their inexperience, novice drivers rarely 

crash while they are being supervised by adults (Mayhew, Simpson, & Pak, 2003; Williams et 

al., 1997). 

Many States require parents to certify that learner drivers complete a certain amount of 

supervised driving practice, usually 40 to 50 hours, before they are permitted to obtain an 

intermediate license. Some States stipulate that a certain number of these hours should be 

accumulated during nighttime driving. The expectation is that such requirements will ensure that 

parents provide their teens with at least the specified number of hours of practice driving and 

that this practice will result in more proficient, safer drivers. 

Minimum Required Hours of Supervised Driving for 

Young Beginning Drivers in the United States, April 2011

Hours Required Number of States

100 1

60 2

50 25

45 1

40 10

35 1

30 4

20 2

None 5

Source: Insurance Institute for Highway Safety

Although this requirement is strongly supported by parents and safety organizations, the 

effectiveness of prescribing specific amounts of supervised driving is presently unknown. 

The overall aim of the project was to determine whether the number of supervised driving hours 

required by a State influences 16- and 17-year-old drivers’ involvement in fatal and nonfatal 
vi

crashes. An additional goal was to assess teen driver’s parents and licensing bureau 

employees’ knowledge, awareness, and compliance with the requirements. 

First, FARS data were used to conduct a cross-sectional comparison of 16- and 17-year-old 

driver fatal crash involvement rates throughout the United States to examine whether they were 

related to State’s supervised practice requirements. Second, State fatal and nonfatal crash data 

were examined in a small number of States that had increased their required number of hours of 

supervised driving. Third, telephone interviews with parents of newly licensed teenage drivers in 

5 States examined their awareness, approval, and behaviors in response to these supervised 

driving requirements. Finally, calls to licensing agencies in these 5 States examined how 

licensing officials conveyed the requirements to parents and teenagers. The telephone 

interviews with parents were funded by State Farm Insurance.

Teenage Driver Fatal Crash Involvement – All U.S. Jurisdictions

Fatal crash involvements for drivers of passenger vehicles were obtained from the Fatality 

Analysis Reporting System (FARS) for 1986 through 2007 (22 years) for all 50 States and the 

District of Columbia. These were aggregated by jurisdiction, age group, and quarter (JanuaryMarch, April-June, July-September, and October-December for each year). Each State-quarter 

was then coded for the presence of eight possible GDL components, including required hours of 

supervised driving (none, ≤ 20 hours, 25 to 35 hours, 40 hours, and 50 to 60 hours). The Statequarters were also coded for other traffic safety laws introduced during the study period, such 

as per se blood alcohol concentration (BAC) limits and safety belt laws that could potentially

affect fatal crash involvement rates. Per capita crash involvement rates per State-age groupquarters for 16- and 17-year-olds were estimated using pooled cross-sectional time series 

analysis through negative binomial regression modeling. The objective was to establish whether 

requiring a certain number of supervised driving hours was independently associated with a 

lower fatal crash involvement rate.

Overall, the analyses found no relationship between the number of required supervised driving 

hours and fatal crash involvement among young drivers. For 16-year-old drivers, requiring any 

particular number of supervised driving hours was not associated with changes in fatal crash 

involvement rates. However, when 17-year-old driver fatal crash rates were examined, requiring 

some minimum amount of supervised driving hours first appeared to be associated with higher 

17-year-old crash rates (ranging from 2% to 13%). However, only a few of these estimates 
vii

reached conventional levels of statistical reliability (p < .05) and none of the effect estimates 

remained statistically significant after adjusting for crash rates among older age groups as a 

control for other factors that influence fatality rates, such as safer vehicles. Overall, the analyses 

found no relationship between the number of required supervised driving hours and fatal crash

involvement among young drivers. 

Effect of Changed Supervised Driving Requirements in Individual States

Additional analyses examined whether requiring specific amounts of supervision might affect 

16- and 17-year-old involvement in nonfatal crashes using data obtained from the State Data 

System (SDS) maintained by NHTSA. The original intent was to identify States that made 

changes only to the number of hours of required supervised driving practice without making 

changes to other GDL components. Crash data, however, were either unavailable or 

incomplete in the SDS for most of the States that made changes to their supervised driving 

hours requirement without making other GDL changes. Only Minnesota had adequate data 

available for analysis with for sufficient pre- and post-change periods during which no other 

changes to GDL had been made. 

In an effort to work around the limited availability of data for States that changed only the 

required hours of supervision, States were divided into two types: those that changed both the 

required number of supervised driving hours and the minimum learner permit periods during the 

same year and those that only increased the learner period. This procedure yielded four more 

States for analysis and allowed comparison of the impact of changing the supervised driving 

requirement. The following table summarizes information for the States in this analysis. 

State Change (Mo./Yr. effective) Years in SDS

States that simultaneously increased supervised

driving hours and mandatory holding period

Illinois 0-3 months, 0-25 hours (1/98) 1991-2005

Pennsylvania 0-1 months (9/95), 0-50 hours (1/00) 1991-2001,

2003-2005

States that increased the

mandatory holding period only

South Carolina 0-3 months (7/98) 1997-2004

Virginia 0-6 months (7/96) 1991-2004
viii

To estimate the effects of changes made to supervised driving hours requirements, the fatal and 

serious injury (F/I) crash involvement rates per 10,000 population for 16- and 17-year-olds were 

analyzed using Auto-Regressive Integrated Moving Average (ARIMA) interrupted time series 

analysis. In January 1999, Minnesota added the requirement that beginning drivers obtain 30 

hours of supervised driving practice in the learner phase and 10 additional hours in the 

intermediate phase (for 40 total hours of required supervised driving practice). The ARIMA 

results found that this requirement was not associated with a change in either 16- or 17-year-old 

fatal and serious-injury crash rates. Similar analyses in Illinois, Pennsylvania, South Carolina, 

and Virginia revealed no significant changes in F/I crash rates that could be attributed to an 

increase in the number of required hours of supervised driving.

Parent Interviews

State Farm Insurance provided funding for HSRC to conduct interviews with parents of recently 

licensed teenage drivers to obtain information that might help explain findings of the crash 

analyses. A total of 510 parents in 5 States with varying supervised driving requirements were 

interviewed. These States included Maryland (60 hrs), Minnesota (30 hrs), Ohio (50 hrs), South 

Carolina (40 hrs), and Washington (50 hrs). At least 100 phone interviews were conducted in 

each State. The key issues explored in these interviews included: 

• Awareness of supervised driving requirements; 

• Approval/disapproval of supervised driving requirements; 

• The degree to which parents consider these requirements sufficient; 

• How and when parents kept track of their teens’ driving practice; 

• How much practice teens received during the permit stage; 

• Perceptions about license agency enforcement of supervised driving requirements. 

Overall, 77% of parents believed there was an hours-of-supervision requirement, although this

varied widely across States. Knowledge of the number of hours required was substantially lower 

than awareness that there was some requirement (see figure below). Only one-third (32%) of 

parents knew the correct number of supervised driving hours their teen was required to obtain. 

Knowledge of night driving requirements was even lower. Only 13% of parents knew the 

number of hours that their teens were required to drive at night.
ix

The substantially greater knowledge of the supervised driving requirement among parents in 

Maryland and Ohio strongly suggests that there are systems, procedures, or programs in place 

in these two States that do a better job of alerting parents to this particular requirement. 

Nonetheless, it is noteworthy that even in Maryland and Ohio, only about half of all parents 

could accurately report the number of hours required. 

Most parents (73%) reported that they tried to keep track of the number of hours their teenager 

spent driving during the learner period. Half (52%) said they kept written records or logs. Ninetyone percent of parents in Maryland reported using logs to keep track of their teens’ driving – a 

substantially higher percentage than what was reported in the other 4 States. Maryland provides 

parents with a log when teens obtain a permit, and the log must be turned in to the DMV when 

the teen applies for a license. Although each of the other States requires parents or guardians 

to certify the teenagers have obtained the required amount of practice, only 59% of parents said 

they were required to sign such a form. Parents in Maryland and Ohio were the most likely to 

say they were required to sign forms. 

Almost all (96%) of parents reported that they approve of requiring teens to drive a certain 

number of hours while supervised before they can obtain licenses that allow independent 

driving. Approval of the requirement was high in all 5 States. A series of questions asked how 
x 

many hours of supervised driving parents thought were sufficient to result in teens being ready 

to drive unsupervised. Across all States, the mean number of hours that parents considered to 

be adequate was 56 (median = 50), but this varied by State. 

Unstructured Interviews

To gain insight into parents’ interpretation of supervision requirements, and to learn how they 

dealt with the varying requirements and supporting guidance provided by the States, 

unstructured interviews were conducted with a sub-sample of 56 parents who had completed 

the structured interview (including at least 10 parents from each State). Interviews were 

conducted with some parents who reported they were aware of their States’ supervised driving 

requirement and with others who were not. These interviews were funded separately by State 

Farm Insurance.

Among parents who knew about the requirement, the vast majority, across all States, said it was 

not difficult to complete the required amount of supervised driving. Parents commonly reported 

fitting driving practice into their normal daily routine. A few parents who lived in small towns said 

it was hard to complete the number of required hours because the places they usually drive 

involve only short trips. These parents reported taking special trips or letting their teens drive 

during family vacations in order to meet supervision requirements.

In several of the States, parents reported they did not keep track of the number of practice 

hours their teens completed. This was particularly true in States where the practice 

requirements were not well known (South Carolina, Minnesota). However, among parents who 

used logs to keep track of their teen’s driving hours, the vast majority reported that it was not 

difficult. Many kept the logs in the vehicles and filled them out immediately after each trip. 

Others reported that they filled out the logs on a weekly basis. A few parents reported that it was 

difficult to record the hours because the teen drove with different parents in different vehicles or 

that they kept the logs at home and often forget to fill them out.

Licensing Bureau Contacts

To assess how supervised driving requirements are administered and enforced by licensing 

agencies, licensing agency representatives in each of the 5 States were interviewed. Callers 

posing as either parents or a teenagers asked about licensing requirements for beginning 

teenage drivers. With the exception of Maryland, none of the license agency officials mentioned 
xi

that a particular amount of supervised driving was a requirement during the permit phase of the 

GDL. When specifically asked about a supervision requirement, licensing officials did not seem 

to know the required number of hours without checking. 

Discussion and Conclusions

This is the first study to investigate the independent effect of mandating a specific number of 

hours of supervised driving during the learner stage of GDL. Overall, the analyses failed to find 

evidence in the fatal and serious injury crash databases indicating that requiring 30 to 60 hours 

supervised driving practice results in lower crash rates for teenagers once they begin driving 

without supervision. This conclusion is supported by an analysis of fatal crash involvement by 

16- and 17-year-old drivers from all 50 States and an interrupted time-series analysis of fatal 

and serious injury teen driver crashes in Minnesota following a new requirement for minimum 

hours of supervised driving. Interviews with driver licensing bureau employees and parents 

suggest that the requirement may not be communicated well from the driver licensing bureau to 

the parents, as most of the parents were not aware of the requirement and few could correctly 

identify their State’s requirement. Without accurate records it is difficult to determine how many 

hours of supervised driving teen drivers actually received in each of the States, regardless of 

the State’s requirements. 

It appears that getting the word clearly and effectively to parents about supervised hours 

requirements is far more challenging than many States have realized. Few, if any, States other 

than Maryland require a log to be kept and submitted to the licensing agency. Even in Maryland, 

barely half of parents knew the actual number of hours required. Parents were in favor of 

beginning teenage drivers obtaining extensive amounts of supervised driving experience and of 

requirements to encourage this. They strongly endorsed their States’ requirement – regardless 

of how much or how little it involved. They expressed little concern about being required to 

provide supervision and said they found the time to do the required supervision. They generally 

thought that more hours than mandated were needed and they believed States should be more 

proactive in efforts to ensure that parents provide the amount of supervision their teenagers 

need and gather documentation such as a driving log.
xii

BACKGROUND

Nearly all States in the United States have implemented GDL systems in an effort to reduce 

crashes and fatalities among young drivers (IIHS, 2009). Traditional graduated driver licensing 

systems include three licensing stages: initial learner, intermediate or restricted, and fullprivilege stages. An important component of GDL is the extended learner stage for beginning 

drivers. The learner stage provides an opportunity for novices to accumulate valuable driving 

experience in relatively safe but realistic conditions. Research shows that novice drivers rarely 

crash while they are being supervised by adult drivers (Mayhew, Simpson, & Pak, 2003; 

Williams et al., 1997). 

Prior to the mid-1990s, many States required beginning teen drivers to hold learner permits for 

up to 30 days, while in other States permits were optional. Following the nationwide effort to 

enact GDL programs, 37 States and the District of Columbia now require adult supervision of 

beginning drivers for 6 months, 3 require 9 months, and 7 States require beginning drivers to be 

supervised for a full year (IIHS, 2009). Many States also require parents to certify that their 

teens have completed a certain amount of supervised driving practice, usually 40 to 50 hours, 

before they are permitted to obtain intermediate licenses (IIHS, 2009; see Table 1). In some 

States, a certain number of these hours must be accumulated in specific situations, such as at 

night or in inclement weather. The expectation is that such requirements will ensure that parents 

provide their teens with at least the specified number of hours of practice driving, and that this 

will translate into more proficient – and safer – drivers. 
xiii

Table 1

Minimum Required Hours of Supervised Driving 

for Young Beginning Drivers, April 2011

Hours required Number of States (including DC)

100 1

60 2

50 25

45 1

40 10

35 1

30 4

20 2

None 5

Source: Insurance Institute for Highway Safety

Note: Alabama (30 hours), Alaska (30), Nebraska (50), and 

West Virginia (50) waive the supervised driving requirement 

if teens complete driver education. Oregon (100 hours) 

reduces the requirement to 50 hours for teens who complete 

driver education.

A few studies suggest that teens often meet or exceed the minimum requirement for supervised 

driving hours. Parents in Michigan reported supervising their teens for an average of 75 hours 

during the learner stage, even though only 50 hours of supervised practice is required in that 

State (Waller, Olk, & Shope, 2000). California also requires 50 hours of supervised practice. In 

a survey of California parents, 81% reported their teens had met or exceeded this requirement 

(Williams, Nelson, & Leaf, 2002). 

Support for supervised practice requirements appears to be strong among both parents and 

teens. In a California survey, 94% of parents and 88% of teens said they favored the 

requirement of 50 hours supervised practice (Williams et al., 2002). In Michigan, most parents 

(74%) reported that 50 hours was the appropriate number of hours to require during the learner 

stage (Waller et al., 2000).

Although strongly supported by numerous groups and organizations, the effectiveness of 

supervised practice requirements is presently unknown. Baker, Chen, and Li (2006) examined 

whether the various elements of GDL programs were associated with reductions in fatal crashes 

among 16-year-old drivers. They found that the combination of a holding period of several

months and at least a 30 hour supervised driving requirement reduced fatal crashes by 18% 
xiv

(Baker et al., 2006). However, the independent effect of the supervised driving requirement was 

not reported.

It is also not known how much supervised driving experience is sufficient to achieve the goal of 

developing safe drivers. The few studies conducted to date are inconclusive on whether 

increased practice reduces crash rates among newly licensed teen drivers. McCartt, 

Shabanova, and Leaf (2003) examined crash-involvements among 900 licensed teens who 

reported they had driven an average of about 350 miles with supervision. A detailed analysis 

found no association between the reported amount of practice during the learner stage and the 

likelihood of experiencing a crash post-licensure. Although such self reports – especially from 

inexperienced drivers – must be taken with caution, studies in France and Norway have also 

shown no safety effects following extensive (e.g., 5,000 kilometers) supervised practice (cited in

Simons-Morton & Ouimet, 2007). In contrast, one Swedish study reported a decrease in cashes

following increased driving practice. In 1993, the minimum age for obtaining a learner’s permit in 

Sweden was lowered from 171⁄2 to 16, while the licensing age remained 18. Teens who took 

advantage of the extended learner stage obtained an average of 117 hours of supervised 

practice, and had a 40% lower crash rate once licensed compared to teens who did not obtain 

their permits early (Gregersen et al., 2000). A similar finding has been reported in Austria (cf., 

Twisk & Stacey, 2007). Although encouraging, these studies were not randomized trials and 

self-selection might explain some or all of the differences between the groups. 

Besides the lack of supporting evidence, occasional concerns have been raised about 

requirements for supervised hours. Anecdotal evidence suggests that parents may not keep 

close track of how much driving practice their teens obtain during the learner stage. 

Consequently, there is some question whether these requirements may simply encourage 

parental “fudging” when certifying their teens’ driving experience. In addition, some research 

suggests that it may be unnecessary to establish supervised hours requirements to ensure that 

teens gain substantial amounts of driving experience. For example, North Carolina has no 

requirement for a particular amount of practice during its 12-month learner stage. Nonetheless, 

one study estimated that teens drove approximately 50 hours during just the first 4 months of 

the learner stage (Goodwin, Waller, Foss, & Margolis, 2006). This suggests that lengthy learner 

stages of a year or more may be just as effective – if not more so – than mandating a minimum 

amount of supervised driving. Finally, a supervised driving requirement that applies to all teens 

within a State fails to take into account important individual differences. Some teens may need 
xv

greater amounts of practice before they are ready to drive unsupervised. If a State’s 

requirements are viewed by parents as sufficient – rather than a minimum – then some teens 

may receive less practice than is needed to become safe drivers (Goodwin, Foss, Sohn, &

Mayhew, 2007). 

In summary, a number of organizations recommend GDL systems include 30 to 50 hours of 

supervised driving for novice drivers, some of which should occur during nighttime hours 

(Advocates for Highway and Auto Safety, 2009; American Academy of Pediatrics, 2006; IIHS, 

2009; NHTSA, 2008b). Although this seems a sensible recommendation, there is no empirical

evidence, as of yet, to support such requirements. Presently, it is not known whether supervised 

practice requirements affect the amount of practice teens obtain during the learner stage, or

whether they help to reduce teenage driver crashes. Beyond the possible effect of a policy 

mandating a certain amount of driving practice, there are also no data to indicate that 30 hours 

– or even 60 hours – of supervised driving practice during the learner’s phase produces any 

safety benefit.

The aim of the present study was to determine whether requirements for supervised practice

influence parental or teenage driver behavior during the learner stage of GDL and whether they 

reduce crashes among teen drivers after they are licensed. FARS data were used to conduct a 

cross-sectional comparison of fatal crash rates throughout the United States to examine 

whether crash rates were related to State’s supervised practice requirements. State-specific 

crash data were examined in a small number of States that had increased their required number 

of hours of supervised driving. Telephone interviews with parents of newly licensed teenage 

drivers in 5 States examined their awareness, approval, and behaviors in response to these 

supervised driving requirements. These interviews were funded by State Farm Insurance. 

Licensing bureaus in these 5 States were contacted to determine how they conveyed the 

requirements to parents and teenagers.
xvi
1

CRASH ANALYSES

Teenage Driver Fatal Crash Involvement – All U.S. Jurisdictions

Data

Driver fatal crash involvements for cars, pickup trucks, vans/minivans, and SUVs were obtained 

from the FARS for 1986 to 2007 for all 50 States and the District of Columbia. Driver crash 

involvements were aggregated by jurisdiction, age group (age 16, 17, 20 to 24, 25 to 39, 40 to 

59, and 60+), and quarter (January-March, April-June, July-September, and October-December 

for each year). Hence the unit of analysis was a State-age group-quarter. For each age group, 

in each jurisdiction, there were 88 quarters (22 years x 4 quarters), which amounted to 528

quarters for each jurisdiction (88 quarters x 6 age groups), and a grand total of 26,928 Stateage group-quarters (528 age-group quarters x 51 jurisdictions). 

To estimate age-group-specific crash involvement rates per 10,000 population for analysis, 

State single-year-of-age population estimates were obtained from the U.S. Census Bureau for 

the years 1985 to 2007; population projections were used for 2008. Quarterly estimates were 

interpolated between the annual July estimates.

Coding State GDL Components and Other Pertinent Traffic Laws

Required hours of supervision for novice teen drivers are but a single element of many 

requirements and laws that may affect crash rates. In an effort to statistically isolate the effects 

of supervision requirements, we coded the presence of these potentially influential factors along 

with the number of hours that novice teens were required to obtain.

Several current and historical summaries of State laws and GDL systems have been compiled 

by organizations and researchers. State statutes are complex and are interpreted differently, 

and occasionally incorrectly, by various sources. Rather than attempting to create yet another 

compendium of codes, or relying on only one of the existing systems, we tried to maximize 

accuracy by consulting numerous sources, comparing the codes they used then resolving 

inconsistencies ourselves. These sources and the process used are described more fully in 

Appendix A. 
2 

Each State quarter was coded for the eight different GDL components shown in Table 2. The 

number of quarters per age group and the number of unique jurisdictions contributing at least 

one State-quarter to each category are also shown in the table. A GDL component was 

considered to be in effect during an entire quarter if it was in effect for at least 2 of the 3 months 

in the quarter (+/- up to 5 days).

The GDL elements for each jurisdiction were coded based on a hypothetical teenager who 

applied as early as possible and completed every requirement necessary to avoid additional 

restrictions and obtain a full, unrestricted license at the earliest possible age. Often this included 

the assumption that the teen completed driver education and driver training courses, to avoid 

additional required hours of practice, qualify for an independent license earlier, or avoid license 

restrictions. The exception to this rule concerned “hardship” licenses (e.g., a license allowing 

young teens to drive to and from school only), which were not considered to be a viable option 

for most teens and were therefore not considered to be part of the normal pathway to licensure. 

Nighttime and passenger restrictions were only coded as in effect during a quarter if they 

specifically applied to 16- or 17-year-old drivers. These restrictions sometimes differed in 

application to 16- and 17-year-olds within a State (i.e., in some cases the restriction applied to 

16-year-olds but not 17-year-olds). Furthermore, the restrictions sometimes had multiple stages 

(e.g., no passengers for the first 6 months, and no more than one passenger for the second 6 

months). To make the coding of restrictions consistent across both age groups in such cases, 

the first-occurring phases of multi-stage restrictions as they applied to 16-year-olds were coded 

for the analyses. 
3 

Table 2 

GDL Components Coded, Number of Quarters for Each Age Group in Each Category, 

And Number of Unique Jurisdictions Contributing to Each Category

GDL component Quarters per age group Unique jurisdictions

 categories N % N %

Supervised driving hours (total)

 None required 3,472 77.4 51 100.0

 ≤ 20 hours 137 3.0 6 11.8

 25 to 35 hours 192 4.3 6 11.8

 40 hours 186 4.1 11 21.6

 50 to 60 hours 501 11.2 21 41.2

Nighttime supervised driving hours 

 None required 3,731 83.1 51 100.0

 Some required (from 4 to 10 hours) 757 16.9 32 62.7

Learner permit age (minimum)

 <15 years old 747 16.6 9 17.6

 15 to 15, 5 months 2,050 45.7 28 54.9

 15, 6 months to 15, 11 months 854 19.0 14 27.4

 16 years old 837 18.6 14 27.4

Learner permit length (minimum)

 None 2,330 51.9 44 86.3

 < 3 months 466 10.4 10 19.6

 3 to 4 months 442 9.8 13 25.4

 5 to 6 months 1,069 23.8 42 82.3

 9 to 12 months 181 4.0 6 11.8

Intermediate license age (minimum)

 No intermediate license stage 2,658 59.2 42 82.3

 < 16 years old 389 8.7 8 15.7

 16 to 16, 5 months 1,204 26.8 36 70.6

 16, 6 months to 17 years old 237 5.3 8 15.7

Nighttime driving restriction

 No nighttime restriction 2,952 65.8 45 88.2

 ≤ 10 p.m. 239 5.3 6 11.8

 11 p.m. 212 4.7 10 19.6

 12 a.m. 856 19.1 24 47.1

 1 a.m. 229 5.1 8 15.7

Passenger restriction

 No passenger restriction 3,681 82.0 51 100.0

 0 passengers, < 6 months 91 2.0 5 9.8

 0 passengers, ≥ 6 months 289 6.4 13 25.5

 1 passenger, ≥ 6 months 279 6.2 19 37.2

 2 to 3 passengers, ≥ 6 months 148 3.3 7 13.7

Unrestricted license age (minimum)

 15 to 15, 11 months 252 5.6 5 9.8

 16 to 16, 5 months 2,599 57.9 43 84.3

 16, 6 months to 16, 11 months 304 6.8 13 25.5

 17 to 17, 5 months 842 18.8 22 43.1

 17, 6 months to 18 years old 491 10.9 15 29.4

Note. Each age group had 4,488 quarters across all jurisdictions and years. Quarter percentages do not add to 

100% due to rounding. Jurisdiction counts add to greater than 51 because some jurisdictions changed categories 

over time. Jurisdiction percentages indicate the percentage of the 51 jurisdictions contributing at least one quarter 

to each category across the full 22-year period examined. Nighttime and passenger restrictions were only included 
4 

if they specifically applied to 16- or 17-year-old drivers. Because some restrictions have multiple stages (e.g., 1st 6-

months vs. 2nd 6 months) the first occurring restriction phase alone was coded. Further, because the application of 

restrictions is sometimes different for 16- and 17-year-olds, the quarters were coded based on restrictions as they 

applied to 16-year-olds. Categories were constrained to include at least 5 unique contributing jurisdictions to 

reduce confounding by State-specific effects.

Coding for Other Traffic Safety Laws

During the time period examined, the jurisdictions also changed or implemented several laws in 

addition to GDL (e.g., per se BAC limits, maximum speed limits, and safety belt laws) that could 

also affect fatal crash involvement rates over time. The influence of these changes could 

confound the effect estimates for the GDL components and overall teen licensing systems if 

they were not taken into account in the analyses and adjusted for statistically. Therefore, the 

State-quarters were also coded for the other traffic safety laws shown in Table 3. The sources 

for this information about jurisdictions are provided in appendix SVM.

Table 3 

Other Traffic Safety Laws Coded, Number of Quarters for Each Age Group in Each Category, 

And Number of Unique Jurisdictions Contributing to Each Category

Traffic safety law Quarters per age group Unique jurisdictions

 categories N % N %

Maximum speed limit

 55 mph 726 16.2 51 100.0

 65 mph 2,411 53.7 49 96.1

 70 mph 792 17.6 23 45.1

 75+ mph 559 12.5 13 25.5

Mandatory safety belt use

 None 624 13.9 39 76.5

 Secondary enforcement 2,664 59.4 42 82.3

 Primary enforcement 1,200 26.7 27 52.9

Minimum legal drinking age of 21

 No 210 4.7 29 56.9

 Yes 4,278 95.3 51 100.0

Zero-tolerance for all ages < 21

 No 1,930 43.0 51 100.0

 Yes 2,558 57.0 51 100.0

BAC per se alcohol limit

 ≥ .10 g/dL or no limit 243 5.4 8 15.7

 .10 2,555 56.9 48 94.1

 .08 1,690 37.7 51 100.0

Administrative per se for all ages

 No 1,558 34.7 33 64.7

 Yes 2,930 65.3 41 80.4
5 

Note. Each age group had 4,488 quarters across all States and years. Quarter percentages do not add to 100% 

due to rounding. Jurisdiction counts add to greater than 51 because some jurisdictions changed categories over 

time. Jurisdiction percentages indicate the percentage of the 51 jurisdictions contributing at least one quarter to 

each category across all time. BAC = blood alcohol concentration. Administrative per se = administrative license 

suspension/revocation for BAC ≥ the per se limit, regardless of age or prior offense history. 

Analysis Method

The State-age group-quarters for 16- and 17-year-olds were analyzed with pooled crosssectional time series analysis through negative binomial regression modeling using the SAS 

GENMOD procedure. The natural log of the interpolated quarterly population for each age group 

divided by 10,000 was used as an offset term, resulting in analyses of driver fatal crash 

involvement rates per 10,000 population. Because there was correlation among the quarters, 

due to both clustering by jurisdiction and repeated measurements of the age groups over time, 

generalized estimating equations (GEEs) were used to fit the final models and obtain robust 

variance estimates adjusted for these statistical dependencies.. The working correlation 

structure for the GEE analyses was approximated by a first-order autoregressive structure, 

meaning that State-age group-quarters closer to one another in time were assumed to be more 

similar than those separated by greater time periods. The unit of clustering (i.e., a “subject”) was 

an age group within a State. 

To adjust for possible confounding by long-term secular trends, a linear parameter representing 

continuous time (quarter-years) was included in all models. In addition, a series of three 

indicator-coded variables representing quarter (January-March, etc.) was used in all models, to 

remove variation in crash rates due to seasonal cycles. Interactions of these trend and seasonal 

parameters with jurisdiction, age group, and jurisdiction by age group were included, to allow 

trend and seasonality to differ for each age group within each State. The choice to allow the 

various effects to vary by age group and jurisdiction resulted in very large models, but provided 

the best control for a priori differences among the States that might confound effect estimates.

Indicator variables representing individual year of age (16, 17) were used in the analyses to 

adjust for differences in fatal crash involvement rates associated with driver age group. To 

account for the fact that a priori differences exist in fatal crash rates between jurisdictions due to 

different roadway environments, enforcement, weather, demographic, socioeconomic 

characteristics and other unmeasured State-specific factors, 50 (k – 1) indicator variables 

representing jurisdiction were also included in all analyses. An age group by jurisdiction 
6

interaction was included, to allow for the possibility that State to State differences in fatal crash 

involvement rates differ across age groups.

To adjust for historical artifacts affecting fatal crash involvements associated with 

macroeconomic factors, quarterly unemployment data from the Bureau of Labor Statistics was 

included as a linear term in all analyses. Unemployment interactions with jurisdiction, age group, 

and jurisdiction x age group were included to allow for the relations between macroeconomic 

factors and fatal crash rates to vary for each driver age group within each State. 

The various laws and GDL elements were represented in the models using k - 1 indicator 

variables. To allow for the likelihood that the effects of the various laws differed according driver 

age, age group by law interaction terms were used in all models involving two or more age 

groups. An important implication of this modeling strategy is that it results in effect estimates 

that are relative to drivers of the same age (i.e., the referent group is drivers of the same age). 

Overall tests of effects parameterized by multiple indicator variables were evaluated using 

custom Wald tests based on the robust variance estimates in the GEE models.

Several analyses were conducted involving 16- and 17-year-olds to see how the effect 

estimates varied as a function of two different factors. The first factor was whether, and if so 

which, adult age groups were included in the analyses as covariate series, in an attempt to 

remove additional variation in the teen crash rates that could be accounted for by their shared 

relation with adult crash rates. That is, two different combinations of crash rates for adult age 

groups in each jurisdiction were used to further control for residual State-specific variability that 

might be due to unmeasured factors such as differences in enforcement, weather and roadway 

conditions, gasoline prices, and changes in other laws that were not coded for this study. 

Specifically, the teen crash rates were first analyzed without using adult crash rates as 

covariates. Next, the teen crash rates were analyzed with those for adult drivers 40 to 59

included in the model. Interactions of adult crash rates with age group were included, which 

allowed for the relation between adult crash rates and those of each teen age group to vary.1

 1 The 40- to 59-year-old adult age group was chosen as the initial covariate series because it was the youngest of the 

adult age groups that would not overlap with 16- and 17-year-old drivers during the study time period of 22 years. 

That is, a 17-year-old in 1986 would be 38 in 2007, so to avoid having overlap among drivers between the teen and 

adult crash rate series, the 40- to 59-year-old group was the youngest that could be used.
7

The constraint of having no overlap between the teen and adult covariate series may limit the 

ability to control for unmeasured factors in this case, given the long period of time included and 

the fact that crash rates tend to be more similar between age groups that are closer together. 

Including the crash rates of other, younger adult age groups as covariates, even though some 

portion of them consists of persons who were licensed through the teen licensing system being 

evaluated, might do a better job of removing variability in the teen crash rates resulting from

State-specific unmeasured variables. Therefore, one additional analysis was conducted. This 

included the crash rates for all adult age groups (20 to 24, 25 to 39, 40 to 59, and 60+), with age 

group interactions to allow for each adult covariate series to have a different relation with each 

of the two teen age groups (16, 17). 

The second factor that was varied between analytic models was whether the quarters were 

weighted by the proportion of teenagers in each age group that contributed to each Statequarter. The three analyses just described were repeated with weighting to determine whether 

the effect estimates changed meaningfully and, if so, how. In the unweighted analyses, each 

quarter counted equally towards the effect estimates, whether it represented a relatively small 

number of teen drivers (e.g., Wyoming or Delaware) or a large number (e.g., California or New 

York). To account for the fact that crash rates based on larger numbers of teens provide more 

reliable parameter estimates, each quarter was weighted by the normalized age-group 

population.2 Normalizing the weights to the total number of State-age group-quarters avoids

biasing the variances downward by ensuring they are based on the actual number of quarters 

observed for an age group rather than the total age-group population across all quarters and 

States. 

Results

Table 4 presents the adjusted crash incidence rate ratios, per 10,000 population, for 16- and 17-

year-olds associated with various supervised driving requirements. To conserve space, only the 

models that included covariates for all adult drivers 20 and older (in several ranges separately, 

rather than simply the total) are presented. The findings were highly similar when using only 40-

to 59-year-old adults. Estimates for trend, seasonality, unemployment, jurisdiction, age group, 

the adult crash covariates, other laws and GDL components, and their various interactions are 

 2 The normalized weight for a quarter was the State-specific age group population estimate for the quarter x the 

quotient resulting from the total number of quarters for the age group across all States (4,488) divided by the sum of 

population in that age group across all States [ wn = PopulationAge Group State Quarter x (4488 / PopulationAge Group All 

Quarters)].
8

also not shown, as these were not the goal of the analysis, merely representing factors that 

needed to be controlled in order to establish whether requiring a certain number of supervised 

driving hours was independently associated with a lower fatal crash involvement rate.

Table 4

Adjusted Incidence Rate Ratios for Driver Fatal Crash Involvements per 10,000 Population 

Associated With Supervised Driving Requirements for 16- and 17-Year-Olds, 

United States, 1986-2007

Requirement Unweighted estimates (95% CI) Weighted estimates (95% CI)

16-year-olds

Supervised driving hours (total)

 None required – –

 ≤ 20 hours 1.00 (0.84,1.19) 0.99 (0.84,1.15)

 25 to 35 hours 0.91 (0.78,1.07) 0.90 (0.77,1.06)

 40 hours 1.07 (0.90,1.28) 1.05 (0.87,1.25)

 50 to 60 hours 0.95 (0.82,1.09) 0.93 (0.80,1.08)

Nighttime supervised driving hours

 None required – –

 Some required 1.08 (0.93,1.26) 1.05 (0.88,1.26)

17-year-olds

Supervised driving hours (total)

 None required – –

 ≤ 20 hours 1.05 (0.93,1.19) 1.05 (0.93,1.19)

 25 to 35 hours 1.06 (0.89,1.26) 1.02 (0.89,1.18)

 40 hours 1.13 (0.99,1.29) 1.12 (0.98,1.27)

 50 to 60 hours 1.05 (0.87,1.26) 1.03 (0.87,1.22)

Nighttime supervised driving hours 

 None required – –

 Some required 0.99 (0.84,1.18) 1.03 (0.87,1.21)

Note. All analyses shown included adult crash rates for several age groupings as covariates and are adjusted for 

linear trend, seasonality, unemployment, jurisdiction, age group, interactions of trend, seasonality, and 

unemployment by age group and jurisdiction, age x jurisdiction interactions, as well as all the GDL components and 

laws coded in Tables 2 and 3. Models are adjusted for the crash rates of each included adult age group separately 

for each teen age group in each State (i.e., all covariate x age group x jurisdiction interactions). Results for the

weighted analysis reflect the proportional State representation of each teen age group nationwide. The 95% CI = 

95% confidence interval for the adjusted rate ratios. 

16-Year-Old Nationwide Supervised Driving Requirement Results. Requiring any particular 

number of supervised driving hours was not associated with changes in fatal crash involvement 

rates of 16-year-olds. The estimates across the different numbers of hours required and the 

varying analytic models oscillate around 1.00, but none are reliably different from 1.00 (which 

represents no effect). Requiring that at least some of the supervised driving hours be completed 

during nighttime hours (or during darkness) appeared to be associated with somewhat higher 
9

16-year-old crash rates, but again these estimates were not statistically significant. Overall 

these analyses provide no indication that specific amounts of supervised driving practice, or 

requiring that some portion be completed during nighttime hours, are associated with changes

in the fatal crash involvement rates of 16-year-old drivers.

17-Year-Old Nationwide Supervised Driving Requirement Results. Compared to having no 

required supervised driving hours, requiring some minimum amount of supervised driving hours 

for beginning drivers initially appeared to be associated with higher 17-year-old-driver crash 

rates (ranging from 2% to 13%). However, only a few of these estimates (not shown) reached 

conventional levels of statistical reliability (p < .05) and none of the effect estimates remained

statistically significant when the models adjusted for crash rates among older age groups. As 

with 16-year-olds, requiring that some portion of the supervised driving hours be completed 

during hours of darkness was not consistently or reliably associated with a difference in 17-yearold-driver fatal crash involvement rates. It is important to bear in mind that this analysis 

examined the effects of State mandates of certain amounts of supervised driving for young 

beginning drivers – not supervision requirements that pertain specifically to 17-year-old drivers –

on 17-year-old-driver fatal crash involvement. The choice of an unweighted or weighted model 

made little difference in the final parameter estimates. This is somewhat surprising given the 

very large variations in State populations.
10

Effect of Changed Supervised Driving Requirements in Individual States

The previous analyses attempted to estimate whether requiring supervised driving practice was 

associated with changes in teen crash rates by capitalizing on between- and within-State

variation in these requirements over time. However, the national analysis could only examine 

fatal crash data. Although fatal crashes appear to be similarly responsive to the overall effects of 

graduated licensing systems as less serious crashes, they do represent a very small subset of 

all young driver crashes. Moreover, although complex statistical models can adjust for 

confounding factors thought to influence crashes, such adjustments are subject to measurement 

limitations. Factors that cannot be measured, or which are not thought to influence crashes, 

cannot be included. Accordingly it is useful to examine instances where a State has changed 

the variable of interest – required hours of supervised driving practice in the present case –

creating a natural experiment whose effects can be measured. 

Selection of States

The analyses in the present section examined whether changes in the number of supervised 

driving hours required in selected States were associated with changes in 16- and 17-year-olddriver crash rates. The original intent was to identify States that made changes to the number of 

hours of required supervised driving practice without making changes to other GDL 

components.3 In such cases inferences regarding the impact of the change in required hours of

supervised driving on teen crash rates would be more strongly supported than in situations 

where multiple GDL components were changed simultaneously. However, it was not possible to

fully implement this analytic strategy, for reasons described below. 

SDS crash data were either unavailable or incomplete for most of the States that made changes 

to their supervised driving hours requirement without making changes to other GDL 

components. Only Minnesota had adequate data readily available for analysis with sufficient 

pre- and post-change periods during which no other changes had been made (see Table 5).

 3 This set a difficult standard because States have been highly active in addressing young driver licensing during the 

past decade.
11

Table 5

States That Increased Their Hours of Supervised Driving 

Independent of Other GDL Elements Considered for Analysis

State Change (effective date) Notes

Arizona 0 – 25 hours (1/00) Not in SDS

Maine 0 – 35 hours (8/98) Not in SDS

Minnesota 0 – 30 + 10 intermediate hours (1/99) In SDS 1994-2002, 2004-2005

Rhode Island 0 – 50 hours (7/17/03) Not in SDS

Utah 0 – 30 hours (7/99), 30 – 40 (7/04)

May count 5 hours from simulator and 6 

from driver education towards 

requirement (7/03); In SDS 1991-2004 

Note. SDS = National Center for Statistical Analysis, State Data System.

In an effort to work around the limited availability of States that met the conditions of changing 

only the required hours of supervision, we decided to identify States that made changes to 

supervised driving hours along with changes to minimum learner permit periods, but nothing 

else, and contrast the effects between States. Table 6 shows the States that were considered 

for inclusion in these analyses, along with the dates of relevant law changes and availability of 

data in SDS. States included in the analyses are asterisked in the table.
12

Table 6

Additional States Considered for Analyses of Changes in Supervised Driving Hours

State Change (effective date) Notes

States that simultaneously increased hours of supervised driving and duration 

of the mandatory holding period independent of other GDL elements (n =7)

Florida 6 – 12 months, 0 – 50 hours (10/00) In SDS 1991-2005

Idaho 0 – 4 months, 0 – 50 hours (1/01) Minimum entry age raised to 14, 6 

months (1/01); Not in SDS

Illinois* 0 – 3 months, 0 – 25 hours (1/98) Passenger restriction (6/04); In SDS 

1991-2005; Serious data problems

Kansas 0 – 6 months, 0 – 25+25 intermediate hours (7/99) In SDS 1991-2006

Maryland 0.5 – 4 months, 0 – 40 hours (7/99); 4 – 6, 40 – 60 

(10/05)

Passenger restriction (10/05); In SDS 

1991-2005

Ohio 0 – 6 months, 0 – 50 hours (1/99) Minimum entry age lowered to 15, 6 

months (7/98); In SDS 1991-2005

Pennsylvania* 0 – 1 months (9/16/95); 1 – 6, 0 – 50 hours (1/00) In SDS 1991-2001, 2003-2005

States that increased the mandatory holding period independent of other GDL elements (n = 12)

Alaska 0 – 6 months (1/99) Not in SDS

Arkansas 1 – 6 months (5/99) In SDS 1998-2005

Connecticut 0 – 6 months (1/97) Only 4 months required with DE;

Hawaii 0 – 3 months (7/97) Not in SDS

Indiana 0 – 2 months (1995) In SDS 1991-2000, 2002-2005

Kentucky 1 – 6 months (10/96) In SDS 1997-2005

Louisiana 90 days – 6 months (9/04) Not in SDS

North Dakota 3 – 6 months (8/99) Not in SDS

South Carolina* 0 – 3 months (7/98) In SDS 1997-2004

South Dakota 0 – 6 months (1/99) Only 3 months required with DE; Not in 

SDS

Tennessee 0 – 3 months (1/96) Not in SDS

Virginia* 0 – 6 months (7/96) Learner permit age lowered from 15, 8 

months to 15 (7/95); In SDS 1991-2004

Note. SDS = National Center for Statistical Analysis, State Data System. DE = driver education.

Data

Counts of driver crash involvements in serious (A injury) and fatal (K injury) crashes in cars, 

trucks/pickups, vans/minivans, and SUVS were obtained for Illinois, Minnesota, Pennsylvania, 

South Carolina, and Virginia for the longest contiguous period possible between 1990 and 2005 

for each State, given the limitations of available data from the SDS. Crash counts were obtained 

for Florida for the years 1990 to 2005, for Illinois from 1994 to 2005, for Minnesota from 1994 to 

2002, for Pennsylvania from 1994 to 2002, for South Carolina from 1997 to 2004, and for 

Virginia from 1994 to 2004. The crash counts were stratified by month and age group (16, 17, & 

25 to 39 etc.). 
13

State single-year-of-age population estimates were obtained from the Census Bureau for the 

years 1989 to 2007. Monthly estimates were interpolated between the annual July estimates 

using cubic spline curves for each age group in each jurisdiction. As with the previous analyses, 

the interpolated population estimates allowed the calculation of age-group-specific monthly 

crash involvement rates per 10,000 population for analysis purposes.

Analysis Method

To estimate the State-specific effects of changes made to supervised driving hours, the 

fatal/serious injury (F/I) crash rates per 10,000 population for 16- and 17-year-olds were 

analyzed using ARIMA interrupted time series analysis. This analytic method is the most 

powerful for identifying changes in the teen crash rates per licensed driver before and after 

States changed the numbers of required hours of supervised practice. Although ARIMA 

analyses implicitly control for pre-existing secular trend in crash rates, it is desirable to use the 

crash rates of another age group as a historical covariate to control for other State-specific 

factors that affect all drivers (weather, unique enforcement levels and programs, economic 

conditions, gasoline prices, etc.). The resulting estimates from these analyses are the 

percentage change in crash rates of teen drivers associated with a specified increase in 

required hours of supervised practice. Identifying the precise point at which effects of the 

changed supervised driving requirements could be expected to begin affecting driver crash 

rates required careful inspection of the details of each State’s GDL system, as well as the way 

in which the legislature implemented it (i.e., did they include a “grandfather” clause that delayed 

the true effective date beyond the nominal effective date).

The monthly teen crash rates in each State were first statistically adjusted for trends and 

seasonal variation before the effects of the interventions were evaluated (Lon-Mu Liu, 2006). In 

each State, the monthly crash rates for drivers 25- to 39 years old4

 4 Drivers 25 to 54 are often used as control series for analysis of teenage driver crashes. Analyses conducted earlier 

suggested that a group closer in age to teenagers is a better covariate measure.

were used as covariates to 

model and remove variability in the teen crash rates due to factors affecting drivers of all ages, 

such as changes in enforcement, weather, fuel prices, and other unmeasured factors that are 

specific to each State and which vary over time. The crash rates were log transformed (loge) 

prior to analysis to stabilize series variability and simplify interpretation of the sudden impact 

intervention parameters. Specifically, the coefficient representing the intervention effects (ω) is 

directly interpretable (using the formula 100 x [eω – 1]) as the adjusted monthly percentage 
14

change in the post-intervention series relative to the pre-intervention series (McCleary & Hay, 

1980; McDowall et al., 1980). 

Separate ARIMA analyses were conducted for each of the 5 included States that changed their 

supervised driving hours requirement. Repeated investigations to identify and reduce the bias 

caused by extremely deviant monthly estimates (i.e., outliers) were conducted during both the 

initial modeling and intervention analyses of each series. The final models were deemed to be 

those that best represented the underlying crash behavior, based on the pre-intervention data 

points for each State, using auto-correlation and partial-auto-correlation functions of the series 

residuals (see Brockwell & Davis, 2002, for further information on techniques for model 

identification). 

Results

Minnesota. As noted above, Minnesota is the only State in the SDS that changed the required 

number of supervised driving hours independent of any other simultaneous or temporally 

proximate changes. The monthly F/I crash rates per 10,000 population for Minnesota are shown 

in Figure 1.a. by age group. In February 1997 Minnesota implemented a 6-month learner permit 

phase (no mandatory learner permit was required prior to this date). In January 1999 the State

added the requirement that teens obtain 30 hours of supervised driving practice in the learner 

phase and 10 additional hours in the intermediate phase (for 40 total hours of supervised driving 

practice). The ARIMA results summarized in Table 7 indicate no change in 16-year-old-driver F/I 

crash rates in Minnesota corresponding with the February 1997 introduction of the 6-month 

learner permit. However, there was a 15% decrease in 17-year-old-driver F/I crash rates (p < 

.05) following implementation of the mandatory learner permit. The January 1999 addition to 

require 30 supervised driving hours was not associated with a significant change in the crash 

rates of either age group. The analysis did not find a statistically reliable association between 

the required 30 supervised driving hours and a significant change in the crash rates of either 

age group.
15

Table 7

Summary of Sudden-Permanent ARIMA Models for Fatal/Serious-Injury Crash Rates per 

10,000 Population for 16- and 17-Year-Olds in Minnesota, 1994-2002

Intervention Model component Parameter Lag Estimate t

16-year-olds

February 1997 6-month learner permit ω 0 -0.0023 -0.02

January 1999 30 hours supervised driving ω 0 0.1093 1.07

Control series (25-39-yr-olds) β 0 0.8431 3.50*

Noise AR 12 0.3326 3.46*

Constant 0.5070 4.65*

17-year-olds

February 1997 6-month learner permit ω 0 -0.1633 -2.44*

January 1999 30 hours supervised driving ω 0 0.0763 1.07

Control series (25-39-yr-olds) β 0 0.7095 4.39*

Constant 0.8216 14.30*

*p < .05, two-tailed
16

Figure 1.a. Minnesota Fatal/Serious-Injury Crash Rates per 10,000 Population by Age Group, 1994-2002.

-

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

199401199404199407199410199501199504199507199510199601199604199607199610199701199704199707199710199801199804199807199810199901199904199907199910200001200004200007200010200101200104200107200110200201200204200207200210

Year-Month

Driver Crash Involvements per 10,000 Population

16 17 25-39

February 1997 - six 

month learner permit

January 1999 - 30 hours of 

Supervised Practice
17

Figure 1.b. Minnesota Fatal/Serious-Injury Crash Rate Ratios, by Age versus 25-39-Year-olds, 12-Month Moving Average, 1994-2002.

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

199401199405199409199501199505199509199601199605199609199701199705199709199801199805199809199901199905199909200001200005

200009

200101200105200109200201200205200209

Year-Month

Driver Crash Involvements per 10,000 Population

16 17 16 vs. 25-39 yr-old rate raios, 12 month moving average 17 vs. 25-39 yr-old rate ratios, 12 month moving average

February 1997 - six 

month learner permit

January 1999 - 30 hours of 

Supervised Practice
18

Figure 1.a. contains substantial detail that can obscure general patterns, but a visual inspection 

appears to show a decrease in both 16- and 17-year-old-driver crashes following 

implementation of the 6-month learner permit. However, the analyses control for the trends 

exhibited by the older driver group, which also declined. For clarity, Figure 1.b. reconfigures the 

information to show the 12-month moving averages for 16- and 17-year-old-driver monthly crash 

rate ratios (compared to those for 25- to 39-year-old drivers). Arraying the data this way 

removes secular trends – as reflected by the adult crash rates – in the crash rate plot and 

smoothes out the wide month-to-month variations typically found in monthly crash rates.

Although Figure 1.b. shows an apparent increase in crash rates relative to more experienced 

drivers following enactment of the supervised driving requirement, this increase is not 

statistically significant for either 16- or 17-year-old drivers (t = 1.07 in both cases).

Illinois and South Carolina. As mentioned previously, Minnesota was the only State in the State

Data System that changed the required number of supervised driving hours independent of 

other changes. However, we attempted to obtain some sense of whether adding required hours 

of supervision may have had an independent effect in other States by pairing States that had 

added mandatory hours along with a minimum holding period for the learner permit. For 

example, Illinois added both a 3-month learner period and 25 hours of required supervision (in 

January 1998). By comparing the effects of that combination with the effects of merely instituting 

a 3-month learner period in South Carolina at about the same time (July 1998), we hoped to 

obtain some insight into the possible effects of the hours alone. Although comparing such 

different States is problematic, we judged that this analysis was worth attempting given the very 

limited opportunities to examine effects of requiring supervised hours. Unfortunately, the results 

proved uninformative. 

The Illinois crash data available in the SDS were fraught with problems resulting from changes 

to the crash report form and differential underreporting that varied across time.5

 5 According to the documentation for the Illinois crash data provided by SDS, the Illinois data reflect the following 

changes: (a) a new crash report form starting in 1996; (b) underreporting in 1996 (half the normal number of 

crashes); (c) underreporting of nonfatal crashes in Chicago in 1997; (d) no reporting on nonfatal crashes in Chicago 

for 1998-1999; and (e) a change in injury reporting in 2004. The documentation recommends that the periods 1989-

1992, 1994-1995, 1997-1999, and 2000-present data be viewed as distinct intervals and that 1993 and 1996 be 

viewed as transition years.

In an attempt to 

adjust the analysis for these myriad data problems, temporary step function parameters were 

entered into the ARIMA analyses to model their effects, but the results were less than 

satisfactory. The findings suggest a statistically significant 15.9% increase in 16-year-old-driver
19

crashes following the introduction of the 3-month learner period and 25 hours of required 

supervision, but this was clearly an artifact of the data reporting problems immediately prior to 

this policy change (during 1996). Figure 2 depicts the problematic nature of the crash data in 

Illinois.
20

Figure 2. Illinois Fatal/Serious-Injury Crash Rates per 10,000 Population by Age Group, 1994-2005.

0

1

2

3

4

5

6

7

8

199401199405199409199501199505199509199601199605199609199701199705199709199801199805199809199901199905199909200001200005200009200101200105200109200201200205200209200301200305200309200401200405200409200501200505200509

Year-Month

Driver Crash Involvements per 10,000 Population

16 17 25-39

1996 Low Crash 

Reporting

Change in Injury 

Reporting 2004+ January 1998 - 3 mo. Permit & 25 

Supervised Driving hours (GDL)

June 2004 - 

Passenger 

Restriction
21

Figure 3. South Carolina Fatal/Serious-Injury Crash Rates per 10,000 Population by Age Group, 1997-2004

0

1

1

2

2

3

3

4

4

5

5

199701199704199707199710199801199804199807199810199901199904199907199910200001200004200007200010200101200104200107200110200201200204200207200210200301200304200307200310200401200404200407200410

Year-Month

Driver Crash Involvements per 10,000 Population 

16 17 25-39

July 1998 - 3 Month 

Learner Permit (GDL) March 2002 - + 3 Months LP, 40 

hours Supervised Driving, 

Passenger Restriction
22

Introduction of the 3-month learner period alone in South Carolina did not produce any change 

in crash rates for 16- or 17-year-old drivers (ts = -.83, -.65 respectively; see Figure 3). However, 

comparison with the effect in Illinois cannot be interpreted given the data reporting problems 

immediately prior to this policy change in Illinois. 

Virginia and Pennsylvania. A comparison analysis was also planned for Virginia and 

Pennsylvania. Whereas Virginia merely instituted a mandatory 6-month learner period (in July 

1996), Pennsylvania made a comparable change in the learner period (extending it from 1 to 6 

months), but also added a requirement for new teenage drivers to obtain 50 hours of supervised 

practice. The latter occurred a few years later (January, 2000), rendering the comparison less 

than ideal. The major problem for the planned analysis, however, was that Virginia made 

several changes to its teen licensing system over the years. Most problematic for present 

considerations was that in July 1995 the minimum entry age for a learner permit was lowered 

from 15, 8 months to age 15. As a result, there was an insufficient sustained period prior to the 

implementation of the mandatory 6-month learner period to calibrate a statistical model of young 

driver crashes. In addition, numerous other changes occurred in following years, which 

prevented a stable calibration of post-1996 crash rates.6

Figure 4 shows the crash rates in association with the multiple changes to the Virginia young 

driver licensing system and Table 8 shows the ARIMA results. Of primary interest is the 

absence of any effect of adding the 6-month learner requirement on either 16- or 17-year-olddriver crashes. As an aside, it is noteworthy that when Virginia introduced a full-fledged GDL 

system, in July 2001, 16-year-old-driver crashes dropped notably (following a 6-month period 

reflecting a grandfathering effect whereby those who had begun driving under the previous 

licensing system were allowed to continue under those old rules). The ARIMA analysis indicates 

a statistically significant, 21.9% decrease in 16-year-old-driver crashes after July 2001.

 

6

 A weak passenger restriction allowing no more than three passengers was added in July 1998. Multiple changes 

were made in July 2001: the learner permit entry age was raised to 15, 6 months, the mandatory learner permit 

holding period was increased by 3 months (9 months total), a requirement to obtain 40 hours of supervised driving 

practice was added, a nighttime restriction disallowing driving from midnight to 4 a.m. was added, and the passenger 

restriction was strengthened to allow no more than one passenger younger than 18 until age 17 and no more than 

three thereafter until age 18. Finally, in July 2003 the passenger restriction was further strengthened to allow no more 

than one teen passenger for the first 12 months and no more than three thereafter until age 18. 
23

Table 8

Summary of Sudden-Permanent ARIMA Models for Fatal/Serious-Injury Crash Rates per 

10,000 Population for 16- and 17-Year-Olds in Virginia, 1994-2004

Intervention Model component Parameter Lag Estimate t

16-year-olds

July 1995 Reduced learner age ω 0 -0.1257 -1.23

July 1996 6-month learner permit ω 0 0.0088 0.09

July 1998 Passenger restriction ω 0 -0.0186 -0.25

July 2001 Multiple changes ω 0 -0.2468 -3.30*

July 2003 Changed passenger restric. ω 0 -0.2463 -2.85*

Control series Β 0 1.1272 6.37*

Noise AR 1 0.4072 4.76*

Constant 0.4840 1.46

17-year-olds

July 1995 Reduced learner age ω 0 -0.0798 -1.81†

July 1996 6-month learner permit ω 0 0.0039 0.09

July 1998 Passenger restriction ω 0 0.0177 0.56

July 2001 Multiple changes ω 0 -0.0172 -0.54

July 2003 Changed passenger restric. ω 0 -0.0673 -1.80†

Control series Β 0 1.2084 12.81*

Constant 0.3623 2.11*

*p < .05, two-tailed. †p < .10 

Table 9 and Figure 5 show the results of the ARIMA analysis for Pennsylvania. The increased 

learner permit holding period from 1 to 6 months and added requirement to obtain 50 hours of 

supervised driving practice in January 2000 was associated with a significant 16.6% decrease in 

16-year-old-driver F/I crash rates (p < .05), but no significant change in 17-year-old-driver F/I 

crash rates was associated with this date (p > .05).

Table 9

Summary of Sudden-Permanent ARIMA Models for Fatal/Serious-Injury Crash Rates per 

10,000 Population for 16- and 17-Year-Olds in Pennsylvania, 1994-2002

Intervention Model component Parameter Lag Estimate t

16-year-olds

January 2000 6-mo. learner permit, 50 hrs. supervision ω 0 -0.1816 -1.97*

Control series β 0 0.1450 1.74†

Noise AR 12 0.3899 4.21*

17-year-olds

January 2000 6-mo. learner permit, 50 hrs. supervision ω 0 -0.0129 -0.20

Control series β 0 0.6881 4.17*

Constant 1.5419 12.99*

*p < .05, two-tailed. †p < .10 
24

Although it is tempting to interpret this significant effect as evidence of the benefits of requiring 

50 hours of supervised driving, since Virginia obtained no effect by merely adding a 6-month 

learner period, it is not appropriate to do so. As noted above, it was not possible to obtain a 

reliable indication of the effect of the Virginia learner period because of the short preintervention period for which data were available. The 8-month reduction in the learner permit 

age mid-way through this period further undermines the interpretability of the change parameter 

estimates in the ARIMA analysis. That the Virginia and Pennsylvania interventions occurred 4

years apart raises additional concerns, including the possibility prevailing risk levels may have 

been different for young teenage drivers during these different time periods.
25

Figure 4. Virginia Fatal/Serious-Injury Crash Rates per 10,000 Population by Age Group, 1994-2004.

0

2

4

6

8

10

12

14

16

18

199401199405199409199501199505199509199601199605199609199701199705199709199801199805199809199901199905199909200001200005

200009

200101200105200109200201

200205

200209200301

200305

200309200401200405200409

Year-Month

Driver Crash Involvements per 10,000 Population

16 17 25-39

July 1995 - 

LP Age 15

July 1996 - 6 

Month Learner 

Permit

July 1998 - 1st 

Passenger 

Restriction

July 2001 - LP Age 

15, 6 Months, +3 

Months LP, 40 

Supervised Driving 

Hours, 2nd 

Passenger 

Restriction, Nighttime 

Restriction

July 2003 - 3rd 

Passenger 

Restriction
26

Figure 5. Pennsylvania Fatal/Serious-Injury Crash Rates per 10,000 Population by Age Group, 1994-2002.

0

1

1

2

2

3

199401199404199407199410199501199504199507199510199601199604199607199610199701199704199707199710199801199804199807199810199901199904199907199910200001200004200007200010200101200104200107200110200201200204200207200210

Year-Month

Driver Crash Involvements per 10,000 Population 

16 17 25-39

January 2000 - 6 month 

Learner Permit & 50 Hours of 

Supervised Driving
27

Summary

In summary, the ARIMA analyses proved to be less enlightening than originally expected.

Analyses of Minnesota data did not find a statistically reliable relationship between a 

requirement of 30 hours of supervised driving and either 16- or 17-year-old-driver crash 

rates. Efforts to look at the possible effects of requiring larger numbers of supervised driving 

hours in individual States proved highly problematic. There were several reasons for this, 

including lack of available data for some States of interest, limitations in data quality in 

others, and a mismatch of data availability with time periods during which State policy 

changes of interest were made. In addition, multiple seemingly small – but nonetheless 

complicating – changes to young driver licensing requirements in close succession in some 

States rendered ARIMA analyses incapable of identifying changes in crash data patterns 

subsequent to individual changes.
28

PARENT INTERVIEWS

Structured Interviews

State Farm Insurance funded UNC/HSRC to conduct interviews with parents of teen 

drivers and driver licensing employees. A total of 510 parents in 5 States with varying 

supervised driving requirements were interviewed. These States are Maryland, 

Minnesota, Ohio, South Carolina, and Washington. Table 10 summarizes the supervised

driving requirements in these States. 

Table 10

Supervised Driving and Minimum Age Requirements 

In States Where Parents Were Interviewed

State

Minimum 

Entry 

Age

Mandatory 

Holding 

Period

Minimum 

Amount of 

Supervised 

Driving

Minimum 

Age for an 

Intermediate

License

Required 

Documentation of 

Hours

Maryland 15, 9 

mo.

6 mo. 60 hrs

(10 at night) 16, 3 mo. Log signed by parent/guardian

Minnesota 15 6 mo. 30 hrs 

(10 at night) 16 Affidavit signed by parent/guardian

Ohio 15, 6 

mo.

6 mo. 50 hrs

(10 at night) 16 Affidavit signed by parent/guardian

South 

Carolina 15 6 mo. 40 hrs (10 at night) 15, 6 mo. Affidavit signed by parent/guardian

Washington 15 6 mo. 50 hrs

(10 at night) 16 Affidavit signed by parent/guardian

Source: Insurance Institute for Highway Safety, June 2009 

These States were chosen for a combination of reasons. They offer a range in the 

required number of hours of supervision (30 to 60). In addition, they have a holding 

period of 6 months for the learner permit and a similar minimum age at which the permit

can be obtained. However, they vary in the amount of time between the learner’s permit 

phase and when the intermediate/provisional license is first available. Some States only 

allow 6 months for new drivers to accumulate the required 6 months and required hours 

practice, prior to the licensing age. Others allow new drivers 12 months to get the 
Supervised Driving in GDL 

29

required 6 months and required hours. This is a significant variation because the latter 

provides more time to obtain the required hours of supervision. 

The following are some of the key issues the interviews covered: 

 Awareness of supervised driving requirements, including required number of 

hours of practice and conditions for those hours (e.g., at night);

 The degree to which parents approve or disapprove of these requirements;

 The degree to which parents consider these requirements to be sufficient (i.e., 

whether parents believe that more (or less) practice hours are necessary for 

teens to become safe drivers);

 How and whether parents kept track of their teen’s driving practice;

 How much practice teens received during the permit stage; and

 Perceptions among parents about the degree to which supervised driving 

requirements are enforced by licensing agencies. 

A professional survey research organization with extensive experience doing 

transportation-related surveys conducted telephone interviews. Households were 

sampled randomly from a list of households in each State projected by Survey Sampling, 

Inc. to have one or more teenagers 15 to 17 years old. Interviewers first asked to speak 

with the parent of a teenager. Screening questions ensured that the household included 

a teenager who: (1) was either 16 or 17 years old (or 15 in South Carolina); (2) had a 

license to drive unsupervised; and (3) had lived continuously in the State since obtaining 

his/her learner’s permit. If more than one teenager in the household fit these criteria, the 

interviewer asked the parent to respond to the questions with respect to the youngest of 

these teens. To ensure that the parent who participated in the interview was familiar with 

the teen’s driving experience during the learner stage, the interviewer asked to speak 

with the parent who conducted most of the teen’s supervision. At the conclusion of the 

interview the interviewer thanked the respondent and asked permission for a researcher 

to contact the respondent within the next few weeks for a follow-up interview.

A total of 510 parents were interviewed (at least 100 in each State). The overall 

response rate among qualifying households was 40%. State-specific response rates 

were 58% in Minnesota, 48% in Ohio, 46% in Maryland, 39% in Washington, and 27% in 

South Carolina. The series of questions to identify a qualified household in South 
Supervised Driving in GDL 

30

Carolina was particularly complex and may have discouraged more parents from 

agreeing than in the other States.

Respondent Characteristics

Sixty-three percent of interviews were conducted with mothers. Thirty-six percent were

conducted with fathers and 1% with grandparents. Respondents were most likely to 

describe the area where they lived as a medium size town (40%), followed by a small 

town (27%), country (18%), or large city (14%). Parents’ descriptions of where they lived 

differed by State. Those in Maryland and Washington were more likely to report living in 

medium to large cities compared to parents living in Minnesota, Ohio, and South 

Carolina (χ2 = 35.94, df = 12, p < .001).

Of the teens who were discussed in the interviews, 54% were male. The sex of teens did 

not differ significantly across States (χ2 = 7.49, df = 1, p = .11). The mean age of teens 

at the time of the interview was 16.61 years. This differed significantly across States (F = 

10.32, df = 1, 4 p < .001). The State with the oldest teens was Maryland, at 16.87 years.

South Carolina had the youngest teens, at 16.38 years. This was not unexpected, given 

that Maryland has the highest minimum age for the restricted license among the 5 States 

(16 years, 3 months) and South Carolina has the lowest minimum age (15 years, 6 

months).
Supervised Driving in GDL 

31

Awareness of Supervised Hours Requirements 

Parents were asked several questions about their awareness of their State’s supervised 

hours requirements. Figure 6 shows responses to the question: “Was [he/she] supposed 

to complete a certain number of hours driving with an adult before [he/she] could get a 

regular driver’s license?” 

Figure 6

Overall, 77% of parents believed there was an hours-of-supervision requirement. 

Thirteen percent said there was no requirement, and 10% did not know whether there 

was a requirement. However, as shown in the figure, parental awareness of the 

requirement varied widely across States (χ2 = 124.50, df = 4, p < .001). In two States – 

Maryland and Ohio – awareness was nearly universal. By contrast, fewer than half of 

parents in South Carolina believed there was a requirement. 

 
Supervised Driving in GDL 

32

Parents who were aware of, or thought there was, a requirement for hours of supervised 

driving were asked how many hours were required. Figure 7 shows the percentage of 

parents – among those who believed there is an hours-of-supervision requirement – who

knew the correct number of hours required by State. 

Figure 7

Awareness of the correct number of hours was substantially lower than awareness that 

there was some requirement. Combining those who did not know there was a 

requirement with those who did not know the correct number, though they believed there 

was a requirement, indicates that parental awareness of supervised driving requirements 

is generally quite low (see Figure 8). 

57%

24%

49%

36%

30%

0%

20%

40%

60%

MD MN OH SC WA

Percent of Parents Who Know Correct Number Among 

Those Who Believe a Certain Number of Hours of 

Supervised Driving Is Required
Supervised Driving in GDL 

33

Figure 8

Overall, only 32% of all parents knew the correct number of hours of supervision their 

teen was required to obtain. In 3 of the 5 States, detailed knowledge was extremely low. 

Once again, the difference between States was highly significant (χ2 = 66.99, df = 4, p < 

.001). The information shown in Figures 6 to 8 indicates a clear and systematic 

difference between Maryland and Ohio compared to the other States. Not only do nearly 

all parents know there is a supervision requirement, among those who believe there is a 

requirement, parents in Maryland and Ohio are also more likely to know the correct 

number of hours. This strongly suggests that there are systems, procedures, or 

programs in place in these two States that do a far better job of alerting parents to this 

particular requirement. Nonetheless, it is noteworthy that even in Maryland and Ohio, 

only about half of all parents could accurately report the number of hours required. 
Supervised Driving in GDL 

34

Parents were also asked whether their teen was supposed to complete a certain number 

of hours driving at night. Each of the States requires 10 hours of supervision at night. 

Figure 9 shows the percentage of parents in each State who believed there was a nightdriving requirement. 

Figure 9

Overall, 55% of parents believed there was a requirement for the teen to drive a certain 

number of hours at night. Once again, however, awareness of the night requirement 

differed significantly across States (χ2 = 69.41, df = 4, p < .001). More than 70% of 

parents were aware of the night requirement in Maryland or Ohio, compared to fewer 

than 30% of parents in South Carolina. 
Supervised Driving in GDL 

35

Figure 10 shows the percentage of parents knew the correct number of hours that teens 

were required to obtain at night. 

Figure 10

Overall, only 13% of parents knew the correct number of hours that their teens were 

required to drive at night. Although this differed significantly by State (χ2 = 20.22, df = 4,

p < .001), no more than 25% of parents in any State knew the correct number of hours 

that their teens were required to drive at night. 
Supervised Driving in GDL 

36

Amount of Supervised Driving Practice Teens Obtain

Several questions during the interview focused on how much supervised driving practice 

teens accumulated during the learner stage. Unfortunately, this kind of information is

difficult to obtain accurately. Individuals are not particularly good at estimating time spent 

driving over a period of time. Complicating that task in the present case is that interviews 

were conducted with parents whose teenagers had already held their license for up to 12

months at the time of the interview (or 18 months in South Carolina). Hence, problems 

with recall, or recall bias, were certainly present. 

Overall, 73% of parents said they tried to keep track of the number of hours their 

teenagers spent driving during the learner period. Half (52%) said they kept written 

records or logs (see Figure 11). 

Figure 11

Differences between States were highly significant (χ2 = 143.10, df = 4, p < .001). 

Maryland requires the parents of beginning teenage drivers to keep a log. The log is 

provided at the time the teen obtains a permit and must be turned in to the MVA when 

applying for a license. Hence, it comes as little surprise that 91% of parents in Maryland 
Supervised Driving in GDL 

37

reported using logs to keep track of their teens’ driving. A majority of parents in Ohio

(63%) and Washington (60%) also reported keeping logs. In Ohio a log is not required, 

but the temporary license packet provided to teens and their parents at the licensing 

office when they apply for their permit includes an affidavit that must be signed by the 

parent and notarized, certifying that the teen has obtained 50 hours of supervised driving 

practice. In Washington, a log is provided online along with the parental authorization 

affidavit.

Even among those who had kept records, when asked how many hours their teenagers 

drove while supervised 65% reported they did not know. We examined reports of the 

amount of supervised driving provided by those parents who were willing to offer 

answers. These estimates ranged widely, from 20 to 500 hours, emphasizing the 

estimated nature of this information. Additional detailed analyses suggested that these 

data were not sufficiently reliable to merit reporting. 

Finally, parents were asked the following question: “How hard was it for you and your 

teen to find the time to complete the required number of hours?” Among parents who 

knew the correct number of required hours for their States, only 5% said it was “very 

hard” to find time to complete the hours. Another 28% of parents said it was “somewhat 

hard,” while 67% said “not at all hard.” Since awareness of the correct number of hours 

was very low for most States, responses on this item were not broken out by State. 
Supervised Driving in GDL 

38

Perceptions of Enforcement of Supervised Driving Requirements by Licensing Agencies

Several questions in the interview focused on parents’ perceptions of whether (and how)

the licensing agencies in their States enforce the requirements for supervised driving. 

First, parents were asked whether their States required them to keep logs to record the 

number of hours their teens drove during the permit stage (see Figure 12). 

Figure 12

Overall, 35% of parents reported they were required to keep logs. Once again, the 

difference between States was highly significant (χ2 = 180.00, df = 4, p < .001). Most 

parents in Maryland reported this requirement, whereas almost no parents in Minnesota 

or South Carolina believed this. As mentioned previously, Maryland is the only one of the 

5 States that requires parents to keep logs. In light of this, it is somewhat surprising that 

roughly a third of parents in Ohio and Washington reported that a log was required. In 

both States, logs are made available to parents to help keep track of hours. However, it 

appears some parents did not realize the log was optional.

Those parents who said their States required logs were asked whether they were 

required to turn in the logs when their teens obtained their licenses. In Maryland, 73% of 
Supervised Driving in GDL 

39

these parents reported that they were required to turn in the logs. This suggests that not 

all licensing offices in Maryland may have been diligent in collecting driving logs from 

parents. 

Parents were also asked whether they were required to sign forms stating that their 

teens had completed the required number of hours of supervised driving. Figure 13

shows the percentage of parents who said they were required to sign a form.

Figure 13

Fifty-nine percent of parents said they were required to sign a form stating that their 

teens had completed the required number of hours of supervised driving. The difference 

between States was highly significant (χ2 = 131.30, df = 4, p < .001). Each of the 5 

States requires an affidavit signed by a parent or guardian. Most parents in Maryland 

and Ohio reported that they signed a form, compared to just over half of parents in 

Washington and only a third of parents in Minnesota and South Carolina. If parents in 

these latter States are in fact signing affidavits at the licensing offices, as States 

currently require, it appears that many are not aware of what they are signing.
Supervised Driving in GDL 

40

Approval of Supervised Driving Requirements

One goal of the study was to determine the degree to which parents approve of 

supervised driving requirements and what parents who have recently supervised 

beginning teen drivers believe those requirements should be. As shown in Figure 14, 

approval is quite high for requiring teens to drive a certain number of supervised hours 

before they can obtain licenses that allow independent driving.

Figure 14

Overall, 86% of parents said they “strongly approve” of hours requirements, and there 

was almost no disapproval of supervised hours requirements. Approval of the 

requirement was high in all 5 States (see Figure 15). The only apparent variation was in 

the extent to which parents approved strongly. 
Supervised Driving in GDL 

41

Figure 15

A series of questions was asked to determine how many hours of supervised driving

parents thought were sufficient to result in a teen being ready to drive unsupervised. 

First, they were asked “In your opinion, are teens who have gotten 30 hours of driving 

experience with an adult in the car ready to drive safely on their own?”7 Those who said 

teens were not ready after 30 hours of driving experience were asked whether 40 hours 

was adequate. Subsequent questions asked about 50 hours then 60 hours of driving 

experience, stopping when a level was reached that the parent thought was sufficient. 

Those who believed that 60 hours were still not sufficient were asked the open-ended

question: “How many hours would you say are enough?” Figure 16 shows the number of 

hours of driving experience that parents believe are needed before teens are ready for 

independent driving. 

 

7 For those who responded, “It depends on the teen,” interviewers clarified that the question referred to: 

“most teens generally.”
Supervised Driving in GDL 

42

Figure 16

Across all States, the mean number of hours that parents considered to be adequate 

was 56 (median = 50). However, the most commonly selected number of hours was 30, 

followed by 60. The number of hours that parents consider to be adequate appears to be 

influenced by individual State requirements. Figure 17 shows the percentage of parents 

in each State who reported that they believe various numbers of required hours are 

sufficient. The bar corresponding to what the State required is shown in light blue. 
Supervised Driving in GDL 

43

Figure 17

Number of Hours of Driving Experience Parents Believe Are Needed 

Before Teens Are Ready to Drive Safety on Their Own by State

In Maryland, which requires 60 hours of supervised driving during the learner stage, the 

modal response was 60 hours. The modal response in Ohio was the same as the 

requirement – 50 hours. The distribution in Washington, which also requires 50 hours of 

supervised driving, was bi-modal, concentrating at either 50 or 30 hours. In both 

Minnesota and South Carolina, 30 hours was by far the most common response. 

Minnesota requires 30 hours of supervised driving, whereas South Carolina requires 40 

hours. The similarity of findings in these States may simply reflect a tendency to agree 

with the first option offered to respondents. However, among parents in Minnesota who 
Supervised Driving in GDL 

44

knew the number of hours required (30), a substantial majority (70%) said that was 

enough.

Each of the 5 States has a mandatory holding period of 6 months for the learner’s 

permit. To probe parents’ opinion of the length of the learner stage, we asked the 

following question: “[State] requires teens to have a learner’s permit for 6 months before 

they can apply for a license to drive without an adult in the car. Do you think 6 months is 

about right, too long, or not long enough?” Responses to this question are shown in 

Figure 18. 

Figure 18

Overall, 72% of parents reported that a 6-month learner stage is “about right.” It is 

noteworthy that 26% reported that 6 months was “not long enough” whereas almost 

nobody (2%) said it was “too long.” Responses did not differ meaningfully by State (χ2 = 

8.03, df = 4, p = .43). 

Those parents who said that 6 months was not long enough were asked a follow-up, 

open-ended question: “How many months do you think teens should be required to have 
Supervised Driving in GDL 

45

a permit before they can apply for a regular license?” By far the most common response 

was 12 months, mentioned by 74% of these parents.

Analysis by Length of Time to Complete Learner Stage Requirements

Although each of the States has a mandatory holding period of 6 months, some only 

allow 6 months to get the required 6 months and required hours practice, prior to the

earliest possible licensing age. Others allow 12 months during which teens can amass

the required 6 months and required number of hours. This is important because the 

latter provides more time to obtain the required hours of supervision. Hence, a follow-up 

analysis compared States that allow only 6 months to complete learner stage 

requirements (Maryland, Ohio, and South Carolina) with States that allow 12 months 

(Minnesota and Washington).

As might be expected, teens held their permits for a longer period of time in States that 

allow 12 months to complete the requirements compared to States that allow just 6 

months (8.8 months vs. 7.8 months; t = 4.48, df = 4, p < .001). Figure 19 shows that in 

States where teens had 12 months to accumulate supervised driving, far fewer held the 

permits for the minimum (Somer’s dyx = .21, p < .001). There were no other differences 

between the 6-month and 12-month groups in responses to any other questions, 

including how difficult parents felt it was to complete the required hours in the specified 

time. 
Supervised Driving in GDL 

46

Figure 19
Supervised Driving in GDL 

47

Unstructured interviews

To gain insight into parents’ interpretation of supervision requirements and to learn how 

they dealt with the varying requirements and supporting guidance provided by the 

States, unstructured interviews were conducted with a sub-sample of parents who 

completed the structured interviews. Of the parents who completed the structured 

interviews, the majority (range 63% to 73%) agreed to be contacted for follow-up 

interviews. At least 10 parents were randomly sampled from each State. 

The unstructured interviews with parents examined:

 What parents tried to accomplish during the learner stage;

 The difficulties parents faced in providing supervision and how these affected the 

type and amount of supervision; 

 How parents learned about supervised practice requirements;

 Parents’ understanding of the rationale for required hours practice;

 How and whether parents kept track of their teen’s driving practice;

 Whether the supervised driving requirement affected how and when teens 

obtained practice;

 Procedures parents encountered at licensing offices for certifying that teens had 

completed the required number hours of practice; 

 How parents decided when their teen was ready to obtain a license to drive 

unsupervised; and

 Overall thoughts about their experience and advice for other parents.

Respondent Characteristics

Of the 510 parents who participated in the structured interview, 343 agreed to be 

contacted to complete the follow-up unstructured interview. Of the parents contacted, 5 

subsequently refused to participate. A total of 56 unstructured interviews were 

conducted with parents who previously completed the structured interviews. Sixty-six 

percent of interviews were conducted with mothers and the remaining 34% of interviews 

were conducted with fathers. Of the teens who were discussed in the interviews, 55% 

were male. As shown in Table 11, we conducted interviews with some parents who 

reported that they were aware of their States’ supervised driving requirement and others 

who were not. 
Supervised Driving in GDL 

48

Table 11

Unstructured Interview Respondents’ Awareness of 

Supervised Driving Requirement by State

Aware of 

Requirement

MD

(n = 10)

MN

(n = 10)

OH

(n = 12)

SC

(n = 13)

WA

(n = 11)

Yes 9 5 11 9 8 

No 1 5 1 4 3 

What Parents Tried to Accomplish During the Learner Stage

One of the topics discussed with parents was whether they had things they wanted to 

accomplish with their son or daughter during the learner period and, if so, what those 

were. The majority of parents mentioned they wanted to make sure their teens had 

exposure to a variety of driving situations and roadways before they drove on their own. 

Several specifically noted that they wanted their teens to get experience driving on 

interstates and highways. Many parents also stated they wanted to make sure their 

teens had practice driving at night and in different weather conditions (such as ice and 

snow); however, some parents explicitly mentioned that a 6-month permit phase was too 

short because it did not take into account daylight savings time or provide opportunities 

for teens to get driving practice in all seasons and weather conditions. Depending on the 

location and time of year, a 6-month period may provide few opportunities other than 

weekends for beginning drivers to practice during daylight hours; in other cases, 

obtaining practice during darkness could require waiting until 10 p.m. Parents who were 

aware of the supervised driving requirements reported that they wanted to complete the 

hourly driving requirement, but no clear indications emerged from the discussions 

regarding how the requirement influenced the ways they went about teaching their teens 

to drive. 

Parents’ Opinions Concerning Mandated Hours of Supervision 

In an effort to understand the reasons that parents so strongly approve of the 

requirement for teens to amass a certain amount of supervised driving, this issue was 

discussed as part of the unstructured interviews. Because some parents did not know 

their State’s required number, the interviewer mentioned this number in a matter-of-fact 

manner when bringing up the issue. Although we anticipated that a variety of issues 
Supervised Driving in GDL 

49

might be mentioned, parents’ responses invariably focused on the number of hours 

required rather than on difficulties the requirement created or the perceived 

appropriateness of such mandates. Opinions varied as a function of the States’ specific 

requirements. In South Carolina, the majority of parents mentioned that they thought that 

30 hours practice was not enough and more hours should be required. In addition, many 

parents mentioned that teens are allowed to get their licenses too early in South 

Carolina (where an intermediate license can be obtained at age 15 1⁄2). 

There was no consensus in opinion among parents in Minnesota regarding the 

supervised driving requirement. About half of the parents in Minnesota thought the 30-

hour requirement was sufficient and the other half thought it was inadequate and 

recommended that the State require anywhere from 50 to 200 hours. Likewise, In Ohio 

and Washington approximately half of the parents reported that 50 hours of supervised 

driving was appropriate and the other half thought it was not enough. There was much 

more agreement among parents in Maryland. The majority of parents in Maryland 

reported that 60 hours was a reasonable requirement, but most said that more practice 

would be even better. 

Regardless of their opinions about their States’ specific hourly requirements, parents in 

all 5 States broadly agreed that learning to drive is an individual process, mentioning in a 

variety of ways that each teenager has unique needs. Many parents reported that it was

hard to say how many hours were enough because “all teens are different.” A parent in 

Washington said, “Putting guidelines in place is not enough. Ultimately they have to 

prove they can drive well.” Some parents also stated that no number of hours would be 

enough because 16-year-olds are “just too young to drive.” Several indicated awareness 

of the recent reports that adolescent brains have not yet fully developed (cite Giedd), so 

no number of hours was considered sufficient. Similarly, a Maryland parent stated, “Sixty 

hours doesn’t make teens safer drivers, just because they are teens.”

How Parents Decided When Their Teens Were Ready to Obtain Licenses 

When queried about how they decided when their teens were ready to get licenses, 

parents did not mention the hourly driving requirement as a deciding factor. Although 

they reported that they wanted to ensure their teens completed the required hours, they 

did not assume that indicated their teens were ready to get licenses. Rather, they tended 
Supervised Driving in GDL 

50

to base the decision on their teen’s individual driving skills and demeanor while driving 

(e.g., comfortable, timid, overly confident). The majority of parents reported that they 

allowed them to get licenses when they felt “comfortable” with their teens’ driving skills 

and demeanor. However, some parents prefaced this with the comment that they would 

never feel completely comfortable with their teens driving on their own, although they 

acknowledged that the teens would only become better drivers through experience. 

Feasibility of Completing Supervised Driving Requirements

One of the issues discussed with parents was the ease or difficulty of, and barriers to, 

spending many hours supervising their teens’ driving. Across all States, the vast majority 

of parents said it was not difficult to complete the driving practice. Parents commonly

reported that they fit driving practice into their normal daily routines. Many mentioned

that they let their teens drive every time they were in the car. Most parents also reported 

that they had a few specific sessions for their teens to practice specific skills, such as 

parking, or to practice in particular road/weather conditions. A few parents who lived in 

small towns said it was hard to complete the number of required hours because the 

places they usually drive are not very far away. These parents reported having to take 

special trips or letting their teens drive a lot on family vacations in order to meet the 

requirements.

How Parents Learned About Supervised Practice Requirements

In view of the low awareness of supervised driving requirements in some of the States, 

we talked with parents how they had learned about these requirements to see whether 

there are variations in how States acquaint parents with the requirement. Among parents 

who knew about the requirements, the majority reported that they obtained information 

either from the driver-licensing bureau or through their teens’ driver education courses. 

However, a number of differences were noted between States. In South Carolina, where 

awareness was quite low, parents’ responses were more varied and included other 

parents, their teens, the Internet, driver education instructors, and from the Department 

of Motor Vehicles when their teens received their learner’s permits as sources of 

information about the requirement. 

In Minnesota, all of the parents reported that they learned about the supervised driving 

requirements from their teens' driver education program. This is most likely due to the 
Supervised Driving in GDL 

51

fact that driver education is required for all teens in Minnesota before they can receive 

learner’s permits. Conversely, in the other States there are various requirements 

concerning the sequence to obtain a learner’s permit and completing driver education. In 

South Carolina, Maryland, and Ohio a teen can receive a permit before completing driver 

education. In Washington a teen can receive a permit either concurrently with driver 

education or prior to completing driver education.

In Washington, parents reported that they found out about the hourly requirement either 

from the Washington State Department of Licensing or their teens’ driver education 

programs.8

 Similarly, in Ohio parents were split equally in whether they found out about 

the requirement from the teens’ driver education program or from the Bureau of Motor 

Vehicles. In Maryland, the majority of parents said they found out about the requirement 

from the Motor Vehicle Administration when their teens received their learner’s permits. 

Parents’ Understanding of the Rationale for Required Hours Practice

An important question is how parents interpret State requirements for a particular 

number of hours supervised driving. In the structured interviews, there was a tendency 

for parents to view the number required number of hours in their State as sufficient to 

produce a safe driver. Accordingly we explored this issue with parents by asking why 

they thought there was such a requirement, how it came about, etc. Few parents were 

certain about why their State had a particular hourly requirement. Most said they thought 

there must have been some type of scientific evidence showing that a certain amount of 

driving practice would make teens safer drivers and reduce crashes. Parents also 

reported that they thought supervised driving was required because teens do not get 

enough driving practice during driver education courses.

How Parents Kept Track of Their Teens’ Driving Practice 

Discussions also focused on whether, and if so how, parents tried to keep track of the 

amount of practice their teens obtained. In South Carolina, the majority of parents 

reported that they did not keep track of the number of hours their teens drove. However, 

half of the parents mentioned that if a State is going to require a certain amount of 

 

8 This parallels the two paths to licensure in Washington, as discussed above. A teen who is enrolled in a 

driver education class can get a learner permit at age 15. Those not enrolled in a driver education class can 

get a permit when they are 151⁄2 or older and then must take driver’s education before receiving an 

intermediate license.
Supervised Driving in GDL 

52

supervised driving, then there should be a system in place – such as the mandatory use 

of a log – to verify the hours are completed. Similarly, in Minnesota the majority of 

parents said they did not write down the number of hours their teens drove. Given the 

low awareness of the supervised driving requirement in South Carolina and Minnesota, it 

comes as little surprise that few parents in these States kept track of their teens’ driving.

In Washington, approximately half of the parents reported that they kept logs of their 

teens driving. Parents were most likely to report using logs as part of their teens’ driver 

education courses. These parents reported that the driver education instructors sent 

home driving logs and assigned different driving practice tasks each week. Parents in 

Washington also thought teens should be required to turn in logs showing the driving 

hours had been completed. 

The majority of parents interviewed in Ohio reported that they used logs to keep track of 

their teens’ hours. This is interesting given the fact the Ohio Bureau of Motor Vehicles 

does not require a log to be turned in. However, several parents noted that the licensing 

office encourages parents to complete logs and some parents reported that they thought 

they would be required to submit them to the licensing agency for their teens to obtain 

licenses. One parent said, “They [licensing office representative] recommended that we 

keep a log and they went over the specifics on how to keep track of the hours.”

In Maryland, most parents reported that they kept track of their teens’ driving practice 

because they were required to turn in logs when their teens applied for intermediate 

licenses. They also reported that when their teens received a learner permit the parent 

was given a driving log with instructions for completing the supervised driving 

requirement. 

In almost every State, a couple of parents mentioned that they kept track and recorded 

their teens driving hours in a logbook in order for their teens to qualify for insurance 

discounts. State Farm’s Steer Clear Program was mentioned repeatedly as the reason 

they kept logs. 

Among the parents who used logs to keep track of their teens driving hours, the vast 

majority reported that it was not difficult. Many stated they kept the logs in the glove 
Supervised Driving in GDL 

53

compartment and their teens filled out the logs immediately after each trip. Some 

parents reported that they filled out the logs on a weekly basis. A few parents reported 

that it was difficult to record the hours because the teens drove with different parents in 

different automobiles or that they kept the logs at their houses and often forget to fill 

them out. 

Overall Thoughts About Their Experience and Advice for Other Parents

A theme among all parents was that they were surprised about how little teens know 

about driving, especially the many aspects of driving that seem to come naturally to 

parents as experienced drivers. As a parent in Washington said, “An unconscious 

response is a sign of a good driver that teens do not initially possess.” Parents noted 

that teens lack the ability to – or at least don’t – anticipate the actions of others, instead 

assuming that other drivers will drive properly (e.g., stop at stop signs and red lights, not 

back into them in a parking lot). Numerous parents emphasized that the only way for 

teens to gain this type of awareness and automatic response is through “practice, 

practice, practice.”
Supervised Driving in GDL 

54

Licensing Bureau Interviews

To assess how supervised driving requirements are administered and enforced by 

licensing agencies, UNC/HSRC held informal conversations with a representative in 

each of the 5 States where parents were interviewed. Research team members posing

as either a parent of a teenager, or a teenager, contacted bureau representatives and 

asked questions pertaining to licensing requirements for beginning teenage drivers. In 

Minnesota, Ohio, and Washington the representatives were at local offices and in South 

Carolina and Maryland the representatives were at central call centers. In Maryland, the 

telephone number for the central call is the only number that is made publicly available. 

In South Carolina we called a local office but were then prompted by a voice messaging 

system to contact the central call center for a detailed inquiry.

These interviews focused on:

 How supervised driving requirements are conveyed to parents and/or teenagers; 

 Procedures at licensing offices for certifying that teens have completed the 

required hours of practice; 

 Recommendations to parents/teenagers who report they have not kept track of 

the number of supervised hours a teen has acquired.

Results

Licensing bureau employees were first asked about requirements for a teenager to get a 

license. In all of the States, the licensing representatives indicated that a learner permit 

must be held for a required time period. However, with the exception of Maryland, none 

of the licensing representatives mentioned that the teen needed to complete a specific 

number of hours of supervised driving during the permit phase. In Maryland, the 

representative explained that 60 hours of supervised driving had to be completed with a 

parent and 10 of those hours had to be completed at night. 

In each of the States other than Maryland, the interviewer probed further to see if the 

agency represented knew about the supervised hours requirement by saying, “I’ve heard 

there is some type of hourly driving requirement for teens before they can get a license.” 

In Minnesota, the representative gave the correct number of hours after being prompted. 

In South Carolina, the representative said she was unsure, then looked up the 

requirements and shared the correct information with the interviewer. In Ohio and 
Supervised Driving in GDL 

55

Washington, the representatives mentioned the hourly behind-the-wheel training 

requirement that must be completed as part of the States’ driver education curriculum, 

but they did not mention the supervised driving requirement. In these cases, the 

interviewer probed further by saying, “I’ve heard that parents are supposed to complete 

a certain number of hours of driving practice with their teen before the teen can get a 

license.“ After this last probe, the representative in Ohio stated the correct number of 

day and nighttime hours. In Washington the representative said, “I think it’s 50,” but she 

did not mention the nighttime driving requirement.

After establishing that supervised hours were required, representatives were asked 

whether any forms had to be signed regarding this requirement. In all of the States, the 

licensing bureau representatives reported that a form had to be signed by the parent 

certifying the supervised driving hours had been completed. In Maryland, the only State

that requires a driving log, the representative also stated that a log had to be completed 

and signed by a parent certifying that the hours were completed. 

Finally, the caller told the licensing bureau representative that she had not kept track of 

the hours of supervision. In Maryland, the representative said that the log had to be 

completed and signed by the parent. She said that it must include the date, along with 

the start and end time for each driving session. She stated, “The log shows that you get 

the experience that you need to actually prepare you for a driver’s license.” She then 

offered to mail the log to the caller. In all of the other States, the representatives told the 

interviewer that as long as the parent thought the teen had completed the hours then 

they just had to sign the affidavit. In Washington the representative mentioned that, “We 

just don’t question you.”
Supervised Driving in GDL 

56

DISCUSSION AND CONCLUSIONS

This is the first study to investigate the independent effect of mandating a specific 

number of hours of supervised driving during the learner stage of GDL. Overall, the 

national database analyses failed to find evidence that a 30- to 60-hour supervised 

driving State requirement affects crash rates for teenagers once they begin driving 

without supervision. This conclusion is supported by an analysis of fatal crash 

involvement by 16- and 17-year-old drivers from all 50 States and an interrupted timeseries analysis of teen driver crashes in Minnesota following a new requirement for 

minimum hours of supervised driving in that State. Interviews with parents in 5 States 

that require a range of 30 to 60 supervised hours suggest that not many parents are 

aware of their State’s supervised driving requirement, few understand specific driving 

activities the parents should accomplish during the supervision, and many believe teens 

need more practice and a longer time before they become fully licensed. Only one State

verifies the number of supervised driving hours and requires parents to turn in a 

completed log. 

Crash Analyses

A cross-sectional comparison of fatal crash rates throughout the United States

examined whether crash rates were related to State’s supervised practice requirements. 

This pooled cross-sectional time series analysis carefully controlled for the possible 

effects of other elements of States’ young driver licensing systems, other traffic safety 

laws, and other factors such as population and general economic conditions to isolate 

the possible effect of mandated hours of supervision. This national analysis did not find 

any fatal crash effects among 16- and 17-year-old drivers by differing required amounts 

of supervision. 

There are limits to the usefulness of national analyses of traffic safety regulations, 

especially those as complex as GDL. The national analysis only examined fatal crash 

data. Although fatal crashes seem to be responsive to the overall effects of graduated 

licensing systems, they represent a very small subset of all young-driver crashes. For 

these reasons, the effects of changed supervised driving requirements in individual 

States were also examined.
Supervised Driving in GDL 

57

The most direct evidence concerning whether a supervised-hours requirement 

influences crashes comes from Minnesota. In 1999, Minnesota introduced a new 

requirement that teens obtain 30 hours supervised practice during the learner stage of 

GDL, plus an additional 10 hours in the intermediate phase for a total of 40 hours 

supervised practice. This requirement was implemented independent of any other 

changes to the State’s GDL system. An interrupted time-series analysis did not find a 

significant change in the crash rates of either 16- or 17-year-old drivers after Minnesota 

implemented the new supervised driving requirement. The interview data provide a 

possible explanation for this finding. Parents who had recently been through the process 

of licensing a teenage driver in Minnesota were largely unaware of the requirement that 

they supervise their teen’s driving for any period of time, and even fewer – just 15% – 

knew the requirement was 30 hours.9 Moreover, in the unstructured interviews, none 

mentioned the additional 10 hours they were supposed to provide during the 

intermediate license period. It is not possible to know whether there might have been an 

effect for this requirement had it been more effectively communicated to the parents of 

new teenage drivers and parents recorded the amount of supervised driving their teen 

accomplished. 

Unfortunately, for a series of reasons, the findings from the State analyses in Illinois, 

South Carolina, Virginia, and Pennsylvania cannot be interpreted as providing even 

suggestive evidence about the effect of adding a requirement for hours of supervision. 

Parental Knowledge, Understanding and Beliefs

Telephone interviews with parents of newly licensed teenage drivers in 5 States with 

varying supervised driving requirements examined their awareness, approval, and 

behaviors in response to these requirements. Parental knowledge of State requirements 

for supervised driving varied widely among the 5 States. Generally, awareness of the 

hours requirement appeared largely dependent on the mechanisms within each State to 

inform parents about, and encourage them to comply with, the requirement. For 

example, in Maryland, licensing agency representatives are careful to draw attention to 

the requirement and that a parent is required to turn in a log. The result is that nearly 

every parent interviewed (96%) knew of the requirement. Ohio provides a similarly 

 

9 It is important to keep in mind that these interviews were conducted in 2008, with parents of teens who had 

obtained unrestricted licenses during the preceding year. Awareness of the 30-hour requirement may have 

been different during the period more closely following its introduction in 1999. 
Supervised Driving in GDL 

58

successful approach to ensuring that parents know that they are required to provide a 

specified amount of supervision. Although a driving log is not required, it is made clear to 

parents when their teens obtain learner permits that the parents will be expected to 

certify, with a notarized affidavit, that the teens have obtained the required amount of 

supervised driving. Agency representatives explain to parents that the only way they can 

know this has been accomplished is by keeping a log, and a sample is provided. Not 

surprisingly, 98% of parents are aware of the hours requirement.

By contrast, parents in Minnesota and South Carolina are merely asked to affirm – at the 

licensing office when the teen returns to obtain an intermediate license – that they have 

done the required amount of supervised driving. They are not provided with a log or 

encouraged to keep track of hours. Moreover, our conversations with personnel at 

licensing offices suggest the message about the requirement is unclear and sometimes 

contradictory. It is not surprising that parents are confused about what they are expected 

to do and about the States’ seriousness about the requirement.

It is noteworthy that even in Maryland and Ohio, where nearly all parents realized there 

was a supervised hours requirement, only about half could accurately report the number 

of hours required. This may suggest that regulatory concern with details about the exact 

number of hours to be required, or whether a certain number of these hours must be 

done at night or in other settings, may be futile. It was clear from the unstructured 

interviews that parents focused less on the number of hours practice being obtained, 

and more on how their teenager was doing with the myriad driving tasks and conditions 

that the parents could observe. Few allowed their teens to obtain licenses, regardless of 

the number of hours of driving amassed, if they did not believe they were sufficiently 

accomplished drivers to begin driving on their own. Nearly all parents mentioned a belief 

that their teenagers just needed to do a lot of driving to obtain plenty of experience, and 

they seemed to have a general plan to accomplish this.

Findings

It appears that getting the word clearly and effectively to parents about supervised hours 

requirements is far more challenging than many States have realized. Few, if any, States 

other than Maryland require a log to be kept and submitted. Even in Maryland, barely 
Supervised Driving in GDL 

59

half of parents know the actual number of hours required. Accordingly, it is unlikely that 

awareness is better in States that do not include a verification log. 

 

It is important to bear in mind that lack of awareness by parents is not necessarily the 

only, or the most important factor explaining the lack of evidence for an influence of 

mandated hours-of-supervision on crashes. Despite lack of awareness of specific hour 

mandates, parents reported providing a substantial amount of supervision during the 

unstructured interviews conducted for this study, as well as in other studies (Waller et 

al., 2000; Goodwin et al., 2006). Having obtained a particular number of hours driving 

while supervised may simply be insufficient to influence crash rates. None of the 

amounts currently required in the United States are based on evidence showing that 

subsequent crash risk is lower if they are amassed. The largest number required by any 

State – 60 – may not be enough to influence subsequent crash risk.

10 

Several Australian States now require 120 hours of supervision (Senserrick, 2007). This 

requirement appears to be based on findings from Gregersen (1997), who reported that 

an average of 118 hours supervised practice was associated with lower crash rates 

among Swedish teenagers. However, given the study design, it was not possible to 

determine whether the lower rate was the result of the extensive practice or the selfselection of study participants. Thus, at least two questions remain: (1) does any amount 

of supervised driving translate into subsequent lower crash risk for teenage drivers and 

(2) if so, does mandating this amount for a population of novice drivers produce a 

populationwide reduction in crashes, given that full compliance cannot be expected? The 

present study suggests the answer to the second is no, at least for requirements of up to 

60 hours of supervision. It also clearly indicates that an effect is unlikely for any 

mandated amount of practice in the absence of more effective mechanisms to ensure 

that parents (and teens) know about such a requirement. 

An additional issue that merits consideration is whether the type, rather than the amount,

of supervised driving experience teenagers are currently obtaining is optimal for 

reducing young driver crashes once they begin driving unsupervised. Perhaps the 

 

10 Although Oregon requires 100 hours of supervised practice, it allows discounting to 50 hours for those 

teens who take driver education courses. This type of time discount has been shown to be 

counterproductive in several studies (Hirsch, Maag & Laberge-Nadeau, 2006; Mayhew et al., 2003), though 

it appears not to have had that effect in Oregon (Raymond et al., 2007).
Supervised Driving in GDL 

60

mandated amounts would be adequate if the required time were spent more 

productively. The possibility that obtained practice is of less than optimal form probably 

does not explain the lack of effect on crashes found in the present study. States’ failure

to effectively promote awareness of the requirements presently in place would have 

precluded the opportunity to stimulate particularly useful kinds of supervision as well as 

activities that may have been less useful. Nonetheless, the nature and quality, as well as 

amount of supervision, merits attention. There is intense interest about this issue within 

the young driver research community, but at present there appear to be no data – or 

guiding theoretical principles – to suggest the type of supervised experience that may be 

necessary or even useful. 

State requirements for teens to obtain some supervised driving at night represent a 

small step toward encouraging novices to obtain supervised experience in a variety of 

conditions. There are several dimensions in addition to night-day (light-darkness) along 

which driving varies that are probably also important. In principle, the ideal would be for

beginning drivers to experience the full range of driving conditions they will deal with 

when they begin driving without supervision – on two-lane rural roads, during inclement 

weather, in fast- and slow-moving rush hour traffic. Ideally, this principle would extend to 

the varying conditions within the vehicle as well, such as distractions caused by multiple 

occupants, or by dealing with the radio, climate controls or MP3 players. The need for 

experience handling such detailed conditions cannot realistically be specified as part of 

licensing requirements, but they could be recommended to parents as part of what they 

should provide in their role as supervisors. Although there is no direct evidence to 

suggest that providing these experiences would produce an effect, encouraging a wide 

variety of experience while supervised, with the full range of conditions to be 

experienced by licensed drivers, is consistent with the general principle upon which 

supervised driving is encouraged or required – novice drivers clearly do learn through 

experience (Mayhew, Pak, & Simpson, 2003).

Two States considered here provide good examples of how to ensure awareness of a 

requirement. Neither, however, provides a model for ensuring parents know, remember, 

or attend to the details of such a requirement. Information obtained from the parent 

interviews suggests a possible alternate approach to ensuring – or at least more 

effectively encouraging – parents to provide beginning teenage drivers with adequate 
Supervised Driving in GDL 

61

experience before they begin driving unsupervised: Adopt a significantly extended (i.e., 

9-month or 12-month) learner stage. 

Although it seems like a long time, a 6-month learner period limits opportunities for 

parents to provide their teens with experience in certain driving conditions. Several 

parents mentioned difficulties they experienced that result from the learner period lasting 

only 6 months. A clear example of how this can occur would be a teenager living in a

State with harsh winter driving conditions who obtains a learner permit in the springtime. 

This leaves no opportunity for the teen to drive on snowy, icy roads or difficult winter light 

conditions during the learner period. The reverse also can be problematic. Extensive 

inclement weather during the winter months limits the time available for highly 

inexperienced teens to begin driving in relatively benign conditions. Another example 

mentioned by parents is that in some States it is unrealistic for teens to obtain much 

supervised driving at night if their learner permit only covers late spring and summer

when it may not be dark until 9 p.m. or later. And again, the reverse can be problematic. 

Teens in some northern States who obtain permits in the late fall have substantially 

diminished opportunity to practice driving under daylight conditions, especially in 

locations where persistent overcast skies commonly exacerbate early sunset times

during winter months. In these locations, weekends may provide the only feasible driving 

opportunity for many. 

Although it is within the purview of parents to overcome barriers like those mentioned, 

and some will marshal the resources to do so, expecting this from all families is contrary 

to the principles of GDL. One of the clear benefits of GDL, in the eyes of parents, is that 

it provides a structure that supports what they want to accomplish, rather than imposing 

barriers. Simply extending the learner period to 12 months would substantially reduce 

the difficulties parents report from misalignment of the learner period with the seasonal 

flow of life. Extending the learner period beyond 6 months may have other benefits as 

well, inducing greater amounts of driving and – if structured carefully – resulting in a 

cohort of intermediate license drivers who are somewhat older and more emotionally 

mature as they begin driving unsupervised (Williams, 2009). 

There appears to be movement toward extending learner periods. In the past few years, 

Illinois and Maryland have moved to a 9-month learner period. Kansas has implemented 
Supervised Driving in GDL 

62

a 12-month learner period, joining 6 other States. Surveys of parents suggest that 

support for a full-year permit is high (Foss, 2007), and the present findings are generally 

consistent with this. Although the majority of parents were satisfied that 6 months was 

long enough, about a quarter reported that 12 months would be more appropriate. 

Moreover, less than half of teens held their permits the minimum 6 months required, with 

about a quarter holding them for 12 months or longer. In Minnesota, 57% of parents 

indicated that their teens held the learner permits for 9 months or longer, perhaps 

reflecting a perceived need for greater driving experience with the seasonal variations in 

roadway and lighting conditions that are found in far northern States.

One of the concerns about mandating a certain number of hours of supervision is that it 

may be interpreted by parents as sufficient rather than the minimum acceptable. There 

was some evidence from interviews that parents do indeed interpret mandates this way. 

Parents generally believed that the number of hours their States required was sufficient 

for teens to become safe drivers, regardless of whether the requirement was 30 or 60

hours, or something in between. Those who participated in the unstructured interviews

generally seemed to believe that such requirements are based on some kind of 

evidence. Nonetheless, the parents we talked with seem not to have been particularly 

concerned about a specific amount of driving practice, focusing instead on their own 

assessment of how well their teens were driving. Most were quite alert to the fact that 

teenagers vary widely in their demeanor, abilities, and learning rates and they seemed to 

focus on those rather than on the formal requirements of the licensing process. With 

respect specifically to hours of supervision, many appeared initially to pay some 

attention to the amount until they realized their teens were likely to easily exceed the 

requirement. In sum, even though parents may believe the hours-of-supervision

requirement represents an objective level that should produce accomplished drivers, this 

does not override their consideration of their own teenagers’ driving abilities and 

demeanors. 

 

Study Limitations

The results of national analyses of traffic safety regulations that involve fitting complex 

statistical models to multifaceted programs like GDL should be interpreted cautiously. 

The primary concern with such analyses is whether fitting models to cross-sectional data 

can adequately identify effects to be found with interventions (cf., Hauer, 2002). Several 
Supervised Driving in GDL 

63

studies have reported effects of the central elements of GDL systems (Baker et al., 

2006; Dee et al., 2005, Morrisey et al., 2006). The analytic approach used here was 

particularly powerful with the ability to examine changes over time as part of the complex 

model-fitting but it was unable to find an association between fatal crash involvement by 

young teenage drivers and mandated hours of supervised driving. 

An important consideration in interpreting the national analysis reported here and 

elsewhere, is that these analyses necessarily include assumptions, some of which are 

inconsistent with how young driver licensing occurs. There is no way, for example, to 

verify in almost every State that young drivers actually get the specified number of 

supervised driving hours, whether it be 30 hours or 60 hours or somewhere in between. 

Most parents are unaware of the requirements. When conducting multijurisdiction 

analyses of programs that differ from State to State it is not possible to represent the 

multiple ways in which a system may influence teenagers. For example, some States 

require teenagers to complete formal driver education classes prior to applying for 

learner permits, whereas others allow learner permits prior to or in conjunction with 

enrollment in driver education. The former approach can produce a delay in the age at 

which many teenagers obtain learner permits, effectively increasing the minimum 

licensing age beyond that specified by statute. The series of requirements and practical 

barriers that initial licensing entails may create a real effect that is not specified in the 

licensing statute. Some of these effects may influence teenagers’ driving exposure and 

resultant crash risk, but they cannot be incorporated in complex statistical models. 

Single State analyses generally address such de facto elements of young driver 

licensing systems more effectively. 

Another assumption upon which multijurisdiction analyses must be based is that all new 

drivers proceed through the licensing steps as prescribed, beginning at the earliest 

possible age, spending the minimum time at each level and not taking advantage of the 

many allowed exemptions (younger driving age if driving only to school; exemption from 

passenger and night restrictions on certain kinds of trips, etc.). This is clearly at variance 

with the ways in which many teens approach the licensing process. Representation of 

reality of even the main elements of GDL systems in multivariable models is crude at 

best. For the analyses conducted in the present study, we made extensive efforts to 

minimize problems like this by including numerous interactions to allow for varying 
Supervised Driving in GDL 

64

operation of GDL elements within individual age groups, single jurisdictions, and single 

time periods. Typically, this is not done in such analyses. 

In a few States, ARIMA interrupted time series analysis was used to estimate the effect 

of hours-of-supervision requirements on crashes because of its ability to avoid many of 

the complications of multijurisdiction analyses. There are constraints on this approach as 

well. The most significant is that ARIMA analysis cannot isolate the effects of 

interventions that occur in close temporal proximity. This presents particular difficulties 

for estimating the effects of young driver licensing policies. Many States have paid 

substantial attention to young driver licensing in recent years, first introducing some 

version of GDL, and then making numerous changes to fine-tune the system. Among the 

States considered in the present study, Virginia was the most active, revising their 

licensing system 5 times between July 1995 and July 2003. The pattern of legislative 

activity also prevented definitive analysis of whether mandated hours of practice 

influenced young driver crashes in Maryland and Ohio where awareness of the 

requirement was high. Maryland simultaneously increased both the duration of the 

learner period and the required amount of supervised driving in 1999 and again in 2005. 

Ohio added both a 6-month mandatory learner period and a 50-hour supervision 

requirement at the same time, in 1999.

Needed Research

The present study suggests States can ensure parents know about required hours of 

supervision and encourage their recordation and completion. It remains unclear, 

however, whether this has any effect on crash rates. The ideal opportunity to examine 

this question would be for a State that does not presently have a requirement for hours 

of supervised driving to enact one. To provide the best chance of identifying an effect, 

should one exist, this would occur at least two years after any other meaningful change 

in the young driver licensing system and not be followed by additional changes for 

another two years or longer. Finally, the system would need to be structured in such a 

way that parents and teens are highly likely to be aware of the requirement, understand 

the details and be motivated to comply. 
Supervised Driving in GDL 

65

Another approach is to obtain data in those few States that either began requiring, or 

substantially increased the number of hours of supervised driving independent of other 

changes. While crash data were not readily available for analysis in this study, they may 

be available later. Such an analysis could provide useful information if the State’s 

requirements are better known by parents and teens. 

Additional research is needed about how parents can be persuaded to ensure that their 

teenager obtains substantial practice in driving conditions that may not occur in the 

family’s daily routine. One option for accomplishing this is through an extended, full year 

learner permit period. Another might be through requiring parents to attend a prelicensing meeting during which they are instructed with the important aspects of their 

role in their teen’s driver licensing experience. Some States have both of these 

approaches in place and it seems likely that more States will be adopting one or both 

approaches, potentially establishing opportunities to examine their effectiveness. 

Conclusion

Parents with whom we talked were broadly in favor of beginning teenage drivers 

obtaining extensive amounts of supervised driving experience and of requirements to 

encourage this. They strongly endorsed their States’ requirement – regardless of how 

much or how little it involved. They expressed little concern about being required to do 

this and said they found the time to do the required supervision. They generally thought 

that more hours than mandated were needed and they believed States should be more 

proactive in efforts to ensure that parents provide the amount of supervision their 

teenagers need and gather documentation such as a driving log. Finally, whenever 

graduated licensing legislation is discussed, usually there is discussion of whether 

States ought to be telling parents how to deal with their children, this “issue of principle” 

was never mentioned during the unstructured interviews, even when parents were given

a clear opportunity raise such concerns. 

Among the 5 States where parents were interviewed, the licensing agencies success in 

familiarizing parents with mandated hours of supervision was not good. Even among the 

two States where awareness of the requirement was quite high, knowledge of the actual 

number of hours required was limited.
66

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Supervised Driving in GDL 

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APPENDIX A 

Identification of details of coded State traffic safety laws

Coding of the GDL components from 1994 to 2007 was based largely on historical 

documentation of changes in State teen licensing laws maintained by the Insurance 

Institute for Highway Safety (IIHS; November 2007) and coding used in the AAA 

Foundation for Traffic Safety Nationwide Review of Graduated Driver Licensing

(AAAFTS; 2007, February). Coding of teen licensing requirements prior to 1994 was 

largely collected from a series of reports published from 1967 to 1996 by the Federal 

Highway Administration called Driver License Administration Requirements and Fees 

(FHWA, 1967, 1968, 1970, 1972, 1974, 1976, 1978, 1980, 1982, 1984, 1986, 1988, 

1990, 1992, 1994, 1996), along with a report titled Comparative Data: State and 

Provincial Licensing Systems (American Association of Motor Vehicle Administrators, 

1999). The information in these reports was also compared to that from the IIHS and 

AAAFTS databases where possible to insure consistency across these sources. 

Discrepancies in the information between sources were resolved by examining State

vehicle codes, chaptered bills, statutes, and regulations, along with searches of other 

published reports on teen licensing laws, historical news articles, and contacts with State

legislative and licensing officials. 

Coding of other traffic safety laws was based on reconciling existing coding obtained 

from several different sources, updating the coding where necessary to extend the time 

period to 2007, and adding coding for Alaska, Hawaii, and the District of Columbia. 

Coding for State maximum speed limits, safety belt laws, zero tolerance alcohol laws, 

BAC per se alcohol limits, and administrative license suspension/revocation for the years 

1982-2006 as used in prior publications by Dee (Dee, 2001; Dee, Grabowski, & 

Morrisey, 2005). The Dee coding was compared with another independent source of 

coding for these laws plus that for statutory minimum legal drinking ages from 1980-

2004 used by Freeman (2007). Coding for minimum State legal drinking ages from 1967

to 2004, including adjustments for grandfathering during the implementation of these 

laws, was obtained from Lovenheim (Lovenheim & Slemrod, 2008). Independent coding 

based on primary research of State statutes from 1976 to 2002 that included coding for 

BAC per se limits, administrative license suspension/revocation, and other alcoholrelated laws, as used in several recent studies was obtained from Wagenaar 
Supervised Driving in GDL 

71

(Wagenaar & Maldonado-Molina, 2007; Wagenaar, Maldonado-Molina, Erickson, Ma, 

Tobler, & Komro, 2007; Wagenaar, Maldonado-Molina, Ma, Tobler, & Komro, 2007). 

The secondary sources of coding detailed above were compared with each other and 

further checked against a number of other available compilations of laws including 

Bernat, Dunsmuir, and Wagenaar (2004), Dang (2008), Hedlund, Ulmer, and Preusser 

(2001), Wagenaar, O’Malley, and LaFond (2001), Zador, Lund, Fields, and Weinberg 

(1989), the Web site for the National Conference of State Legislatures (2004), and the 

Web site for IIHS. Where pre-existing coding was not available (e.g., for Alaska, Hawaii, 

and Washington D.C., and for all States in 2007) or where there were differences among 

the various sources, the quarters were coded based on examination of State vehicle 

codes, chaptered bills, statutes, and regulations, along with searches of other published 

reports on licensing laws, historical news articles, and contacts with State legislative and 

licensing officials. 

Reconciled coding from Dee and Freeman was used for speed limit laws, safety belt 

laws, and zero-tolerance laws in the analyses. The minimum legal drinking age coding 

from Lovenheim and Slemrod was chosen over the other sources because it took into 

consideration the grandfathering of these laws when they were implemented and would 

therefore be more accurate than simply using statutory minimum legal drinking ages. 

The coding provided by Wagenaar for BAC per se limits and administrative license 

suspension/revocation was based on primary review of State statutes by a legal team, 

and was therefore deemed to be most desirable to use in the analyses. As with GDL 

elements, a law was considered to be in effect during an entire quarter if it was in effect 

for at least two of the three months during the quarter (+/- up to 5 days). 


DOT HS 811 550

March 2012

8356-030912-v1