The Iowa graduated driver licensing program: Effectiveness in reducing crashes of teenage drivers

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Abstract

Problem

Graduated Driver Licensing (GDL) programs vary in the United States in terms of implementation and restrictions. The State of Iowa's GDL program is assessed for its effectiveness in reducing crashes among teenage drivers.

Method

Time series analysis was used to evaluate police documented crashes involving 16-, 17-, and 18-year-old drivers over a 10 year period, with an intervention identified at the point of GDL implementation.

Results

After controlling for seasonal trends and auto-correlative effects, a significant reduction in the crash rate of and 16- and 17-year-old drivers was observed due to the GDL implementation. However, there were no significant reductions in crash rates for 18-year-old drivers.

Discussion

The analyses suggest that the Iowa GDL program is effective in reducing the crash rates of 16- and 17-year-old drivers but the effects do not sustain for 18-year-old drivers.

Impact on Industry

The results suggest that the program appears to be working, however further analysis is needed to determine what factors are preventing lasting effects for these teenage drivers.

Introduction

Graduated Driver Licensing (GDL) programs have been implemented in almost every state in the United States as a mechanism to reduce the crashes associated with teenage drivers (Insurance Institute of Highway Safety [IIHS], 2006). These programs are also viewed as an effort to resolve the ‘licensure paradox' that inexperienced drivers need more experience, but more exposure tends to increase crash likelihood (Simons-Morton, 2002). The major goal of such programs is to allow novice drivers to gain experience in less risky driving situations and then gradually move toward full licensure (IIHS, 2006). Dee, Grabowski, and Morrisey (2005) estimated that an additional 131 teenage crash fatalities would occur per year if the GDL programs in the 38 states investigated had not been implemented (as of 2002). There is, however, a concern that the number of restrictions placed on novice drivers, as part of GDL, may limit opportunities to gain experience in high risk situations (McKnight & Peck, 2002). Alternatively, a GDL program may not actually influence risk taking behaviors, it just disallows certain hazardous situations (Ferguson, 2003).

Numerous studies have evaluated the effectiveness of GDLs in terms of what driving factors should be restricted, and what types of assistance should be provided to teenage drivers (Begg et al., 2001, Dee et al., 2005, Ferguson, 2003, Mayhew et al., 2001, Mayhew et al., 2003, Morrisey et al., 2006, Simpson, 2003, Ulmer et al., 2000, Williams and Ferguson, 2002, Williams et al., 2002). Dee et al. (2005) suggested more stringent GDL programs to effectively reduce crashes for teenage drivers. Others have proposed parent or guardian involvement, an important but rarely examined component of the GDLs (Shope & Molnar, 2003). Regardless, there is a growing consensus that GDL programs are effective in reducing the crashes for drivers that participate (McKnight & Peck, 2002). However, some studies do not show a lasting effect for the drivers after they graduate (Mayhew et al., 2003). Ulmer et al. (2000) found that the graduated licensing program in Florida significantly reduced the crash rates for drivers between the ages of 15 and 17 year-olds, but the crash rates of 18 year-olds were not significantly reduced. These results would indicate that the GDL programs are successful in reducing crash risks while teenage drivers are enrolled in the program but return to levels similar to those prior to the program implementation (Agent et al., 2001).

Chen, Baker, and Guohua (2006) have shown that varying program restrictions may influence the effectiveness in reducing the fatal crash rate involvement for 16-year-old drivers. The different levels of effectiveness and varying program restrictions suggest that more research is needed to understand why some programs (or specific program components) may be more effective than others. It should be noted that many of the studies that evaluated GDL programs have examined crash rates (or alternatively crash frequency, number of fatalities or injuries, etc.) as normally and independently, samples over time. However, there are numerous time-varying exogenous variables that impact traffic safety conditions such as seasonal changes, advancements in safety technology, and population changes over time. Regardless of the effect, these changes over time should be taken into consideration in evaluating the GDL's effectiveness, or the conclusions may be misleading.

The implementation of GDL programs vary among states (Hedlund, Shults, & Compton, 2003). They can include restrictions in driving time, number of passengers, and even the use of cellular phones and other distracting devices. In general, these programs have been shown to be effective in reducing the injuries sustained by teenage drivers (Hedlund et al., 2003). Many of the states whose GDL programs have been evaluated include Florida, Michigan, California, Ohio, and Pennsylvania (Hedlund & Compton, 2005). The State of Iowa implemented a GDL program in January 1999 and was 1 of 17 states that implemented a GDL program before 2000 (Shope & Molnar, 2003). Iowa's program requires a minimum of 20 hours supervised driving followed by a 12-month intermediate license period with night time (12:30 a.m. to 5:30 a.m.) and passenger restrictions based on the number of available seatbelts. The intermediate period is only available after the teenager has turned 16. Full licensure can then only be obtained by successful completion of the intermediate period with no traffic violations (17-years-old at the earliest).

One confounding factor associated with the success of the GDL in Iowa is that it is one of a few states that maintain a Minor School Licensing (MSL) program. Within Iowa's MSL program and prior to the GDL program, 14.5 year-old-drivers are allowed to drive after they complete the driver's education class, a knowledge test, and a driving test. They are limited to driving to and from school and after school activities. Another similar program is the “To and From School License” in Nevada (DMVNV, 2006). These teenagers may have more experience compared to teenagers in other states or those who do not participate in the program. The existence of the school license in Iowa suggests that these teenage drivers may differ from those teenagers enrolled in GDL programs in other states. There are two major objectives of this study: (a) to assess whether Iowa's GDL program is effective while the driver is in the program and (b) to assess whether or not the effects are lasting even a year after program completion.

The studies cited thus far would suggest that the implementation of the Iowa GDL program would significantly impact the crash rates of 16- and 17-year-old drivers. It is also hypothesized that a lasting effect may not be observed after the program ends, potentially because of delayed licensure. Within the Iowa program, drivers who have reached the age of 17 and have completed one year in the intermediate phase without any citations are then able to obtain a full driver's license. These same drivers are therefore evaluated at age 18 to evaluate the presence of lasting effects that may result from being a participant in the GDL program.

Section snippets

Method

Crash data from 1995 to 2005 are available as part of the Iowa Department of Transportation's SAVER (Safety, Analysis, Visualization, and Exploration Resource) program. This database includes crash and vehicle characteristics, driver and passenger demographics and injury severity, as well as contributing factors for all the police documented crashes in Iowa. Data from the Iowa DOT's yearly licensure snapshot are also used to establish rates for this analysis. The licensure snapshots document

Results

The number of licenses awarded to 16-, 17-, and 18-year-olds in Iowa is shown in Fig. 1. The proportion of 16-year-olds with intermediate (or provisional) licenses is available from 1995 to 2005. However, the distinction between those who participated in the GDL program and those who did not is not available. Therefore, the year 1999 can include 16-year-olds who are and are not in the GDL program. After 1999, all 16-year-olds who had an intermediate license were required to participate in the

Discussion

The crash risks of teenage drivers remain relatively high compared to other age groups even with the implementation of GDL programs (Ferguson, 2003). The results of this study provide further support for the implementation and continuation of these programs. In Iowa, the GDL program has significantly reduced 16- and 17-year-old drivers' crash rates. However, the GDL program does not appear to significantly reduce the crash rates for 18-year-old drivers which supports the original hypothesis

Acknowledgments

The authors would like to gratefully acknowledge Michael Pawlovich and Scott Falb of the Iowa Department of Transportation for their assistance with the SAVER data and the licensure snapshot data and Jun Yan of the Department of Statistics and Actuarial Sciences at the University of Iowa for his assistance with the modeling. Portions of this manuscript were previously presented at the 2007 Transportation Research Board (TRB) Annual Meeting in Washington, DC. The authors therefore acknowledge

David M. Neyens is a PhD candidate in the Mechanical and Industrial Engineering Department at the University of Iowa. He is also enrolled in the Master's program in the College of Public Health. He received his BS and MS degrees in Industrial Engineering from the University of Iowa in 2004 and 2005, respectively.

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    David M. Neyens is a PhD candidate in the Mechanical and Industrial Engineering Department at the University of Iowa. He is also enrolled in the Master's program in the College of Public Health. He received his BS and MS degrees in Industrial Engineering from the University of Iowa in 2004 and 2005, respectively.

    Birsen Donmez is a post doctorate associate at Massachusetts Institute of Technology. She has a PhD (2007), and MS (2004) in Industrial Engineering, and MS in Statistical and Actuarial Sciences (2007) all from the University of Iowa.

    Linda Ng Boyle is an Associate Professor at the University of Iowa, Department of Mechanical and Industrial Engineering. Prior to her appointments, she was a senior researcher at the U.S. DOT – Volpe Center, and an industrial engineer for the Boeing Company. She received her PhD in Civil and Environmental Engineering and MS in Industrial Engineering from the University of Washington. She also has a BS in Industrial Engineering from the University at Buffalo, SUNY.

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