«by Johnathon P. Ehsani A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Health Behavior ...»
This study was based on crash rates calculated using the number of teens in the overall population. With this approach we were able to determine that the public health impact of GDL on 18-year-old drivers was limited to modest increases in possibleinjuries/POD crashes in Michigan and modest reductions in possible-injuries/PDO crashes in Maryland. A more precise evaluation of the effect of GDL would require the age of licensure (and GDL stage) associated with each individual driver’s crash record.
With this more detailed information, time-to-event analysis could be used to compare first-time crash incidence of teens licensed under GDL to those licensed at age 18.
This study examined the effects of GDL on 18-year-old drivers’ crash rates by comparing states where GDL provisions applied exclusively to 15- to 17-year-old drivers (Florida and Michigan) to a state where GDL applied to novice drivers of all ages (Maryland). The absence of individual licensure data did not allow us to determine whether changes in 18-year-old drivers’ crashes were due to some teens not becoming licensed until age 18.
However, we found that 18-year-old drivers possible-injury/PDO crash rates increased in Michigan and declined in Maryland, which is consistent with the presence of an ‘offset effect’ that reflects the crashes of novice 18-year-old drivers.
GDL components and effective dates in Florida, Michigan and Maryland.
State GDL Components (effective date) Florida 6 month minimum holding period and nighttime driving restriction (7/96) 12 month minimum hold period and 50 hr supervised driving requirement (10/00) Michigan 6 month minimum holding period, 50 hr supervised driving requirement and 12 midnight – 5 a.m. nighttime driving restriction (4/97) Maryland 4 month minimum holding period and 40 hr supervised driving requirement (7/99) 6 month minimum holding period and 60 hr supervised driving requirement (10/05)
^ Rates for Florida and Maryland are based on the crashes after the introduction of the first program, and before the introduction of the second program # Property Damage Only * p.05 Table 4.3. Percentage change in crash rate by state, year-of-age and crash type.
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The aims of this dissertation were to determine the effect of: 1) several components of GDL on 16- and 17-year-old drivers’ fatal crashes; and 2) GDL on 18year-old drivers’ injury crash rates and shed light on a possible mechanism responsible for any increase. Chapters 2 and 3 addressed the first aim, and Chapter 4 examined the second aim.
To address the first aim, we used natural experiments in GDL policy implementation, where a single GDL component was independently implemented during the period 1990 through 2009. Using this sample, we estimated the effect of individual GDL components. Previous research examining the effects of individual GDL requirements and restrictions had rarely been designed to account for the confounding effect of simultaneously implemented GDL components; nevertheless, analysis designs assumed independent implementation of each component. To address this lapse, in chapters 2 and 3, interrupted time series analysis was used to examine the effect of each GDL component individually. Interrupted time series analysis is also ideal for examining changes related to isolated events while accounting for long-term trends in teen drivers’ crashes. This is another way in which these analyses extended previous studies examining the effect of GDL that had used pre- and post-GDL evaluation designs that were unable to distinguish changes in crashes directly attributable to GDL from differences arising from a preexisting trend.
We observed two GDL components that were independently associated with a decline in 16- and 17-year-old drivers’ fatal crash rates: a learner license period that guaranteed a six-month licensing delay and a strong passenger restriction. Supervised driving hours and nighttime driving restrictions associated with a reduction in 16- and 17year-old drivers’ fatal crashes. These findings raise a number of questions regarding how and why certain GDL components appear to affect driving behavior, while others seem not to. There is little question that GDL systems reduce young drivers’ crashes, and the deaths and injuries that result (Foss 2002). However, the relative contribution of each components and how they produce a reduction in crashes and fatalities has remained elusive.
Advances in understanding the development of expertise and mastery can be used to shed light on the findings from Chapters 2 and 3. Research suggests that the acquisition of expertise with a complex task, such as driving, is multidimensional (Rikers and Paas 2005). Expertise requires extended time to develop, and demands deliberate practice (Keating and Halpern-Felsher 2008) that is most effective when it is coordinated and focused on sequentially improving one capability at a time (Ericsson 2005).
Expertise is best acquired when there is a gradual progression from simple to complex conditions (Gagne and Paradise 1961). A final component of expertise is automaticity. A skill becomes automatic when its related competency has become incorporated into a routine (Keating and Halpern-Felsher 2008).
The architecture of GDL is structured to accommodate the development of expertise. Conceptually, the extended learner license is intended to allow teens to gain practice under very safe conditions over a protracted period of time (Mayhew, Simpson et al. 2003), with the objective of developing basic driving skills. Our finding that the introduction of a six-month learner licensure period that guaranteed licensing delay was followed by a significant reduction in fatal crash rates among 16- and 17-year-old drivers suggests that an extended time period for practice driving may be one of the mechanisms responsible for the effectiveness of GDL.