Associations of repeated high alcohol use with unsafe driving behaviors, traffic offenses, and traffic crashes among young drivers: Findings from the New Zealand Drivers Study.

OBJECTIVE: The objective of this study was to describe self-reported high alcohol use at each of the 3 licensing stages of graduated driver licensing and its relationship to drink-driving behaviors, intentional risky driving, aggressive driving, alcohol traffic offenses, non-alcohol traffic offenses, and traffic crashes. METHODS: The New Zealand Drivers Study (NZDS) is a multistage, prospective cohort study of newly licensed drivers interviewed at all 3 stages of the graduated driver licensing system: learner (baseline), restricted (intermediate), and full license. At each stage, alcohol use was self-reported using the Alcohol Use Disorders Identification Test (AUDIT-C), with high alcohol use defined as a score of ≥4 for males and ≥3 for females. Sociodemographic and personality data were obtained at the baseline interview. Alcohol-related, intentional risky, and aggressive driving behaviors were self-reported following each license stage. Traffic crashes and offenses were identified from police records. Crashes were also self-reported. RESULTS: Twenty-six percent (n = 397) reported no high alcohol use, 22% at one license stage, 30% at 2 stages, and 22% at 3 stages. Poisson regression results (unadjusted and adjusted) showed that the number of stages where high alcohol use was reported was significantly associated with each of the outcomes. For most outcomes, and especially the alcohol-involved outcomes, the relative risk increased with the number of stages of high alcohol use. CONCLUSIONS: We found that high alcohol use was common among young newly licensed drivers and those who repeatedly reported high alcohol use were at a significantly higher risk of unsafe driving behaviors. Recently introduced zero blood alcohol concentration (BAC) should help to address this problem, but other strategies are required to target persistent offenders.

Participation in driver education/training courses during graduated driver licensing, and the effect of a time-discount on subsequent traffic offenses: Findings from the New Zealand Drivers Study.

INTRODUCTION: The New Zealand GDL includes a time-discount at the restricted license stage, for attendance at an approved driver education course. This is despite international evidence showing that earlier licensure associated with a time-discount can increase risk for newly licensed drivers. OBJECTIVE: To examine participation in driver education courses and especially those that qualify for a time-discount; compare the profiles of course participants with non-participants; examine reasons for participation; and examine the association between a time-discount and traffic offenses once fully licensed. METHOD: This study was based on the New Zealand Drivers Study (NZDS), a prospective cohort study of newly licensed drivers. Data on driver education courses were obtained at the full license interview (n=1763), driver license and traffic offense data from the NZ Driver Licence Registry, and other data at the NZDS interviews. RESULTS: 94% had heard of and 49% (n=868) participated in a defensive driving course (DDC). No other course had more than 1% participation. Compared with the others, the DDC group were young, non-Maori, and from an area of relatively low deprivation. Through GDL, the DDC group were relatively more compliant with the conditions, and less likely to crash or receive a traffic offense notice. The groups did not differ on personality, alcohol and drug use. The reason most (85%) attended a DDC was to get their full license sooner; 86% (n=748) received a time-discount. The time-discount group were 40% more likely to receive a traffic offense notice on their full license; this reduced to 10% after controlling for other factors. CONCLUSION AND PRACTICAL IMPLICATIONS: The results of this study, when viewed in conjunction with other NZ crash evidence, indicate that a time-discount should not be given for completing a DDC or Street Talk course.

Pre-licensed driving experience and car crash involvement during the learner and restricted, licence stages of graduated driver licensing: Findings from the New Zealand drivers study.

OBJECTIVE: The aim of this study was to determine whether pre-licence driving experiences, that is driving before beginning the licensing process, increased or decreased crash risk as a car driver, during the learner or the restricted licence stages of the graduated driver licensing system (GDLS). METHOD: Study participants were 15-24 year old members of the New Zealand Drivers Study (NZDS) - a prospective cohort study of newly licensed car drivers. The interview stages of the NZDS are linked to, the three licensing stages of the GDLS: learner, restricted and full. Baseline demographic (age, ethnicity, residential location, deprivation), personality (impulsivity, sensation seeking, aggression) and, behavioural data, (including pre-licensed driving behaviour), were obtained at the learner licence interview. Data on distance driven and crashes that occurred at the learner licence and restricted licence stages, were reported at the restricted and full licence interviews, respectively. Crash data were also obtained from police traffic crash report files and this was combined with the self-reported crash data. The analysis of the learner licence stage crashes, when only supervised driving is allowed, was based on the participants who had passed the restricted licence test and undertaken the NZDS, restricted licence interview (n=2358). The analysis of the restricted licence stage crashes, when unsupervised driving is first allowed, was based on those who had passed the full licence test and completed the full licence interview (n=1428). RESULTS: After controlling for a range of demographic, personality, behavioural variables and distance driven, Poisson regression showed that the only pre-licence driving behaviour that showed a consistent relationship with subsequent crashes was on-road car driving which was associated with an increased risk of being the driver in a car crash during the learner licence period. CONCLUSION: This research showed that pre-licensed driving did not reduce crash risk among learner or restricted licensed drivers, and in some cases (such as on-road car driving) may have increased risk. Young people should be discouraged from the illegal behaviour of driving a car on-road before licensing.

Parental influence on adolescent compliance with graduated driver licensing conditions and crashes as a restricted licensed driver: New Zealand drivers study.

AIM: To examine the influence of parental knowledge of, and support for graduated driver licensing (GDL) conditions, parental management of adolescent driving and parental driving behaviour on adolescent compliance with GDL conditions and crashes as a restricted licence driver. METHOD: This research was part of the New Zealand Drivers Study (NZDS), a prospective cohort study of 3992 newly licensed car drivers. NZDS participants were recruited at the learner licence stage, with follow-up aligned with the GDL stages. At the restricted licence stage 1200 parents of NZDS adolescents, aged 15-17 years at learner licensure, were recruited and completed interviews. 895 of these adolescents progressed to their full licence and completed the full licence interview. These 895 parent-adolescent pairs were the study population in this research. Topics examined included parental knowledge of, and support for GDL conditions, management of adolescent driving (driving rules, adolescent vehicle ownership, delaying licensure), and their own driving behaviours. Outcomes examined were adolescent compliance with GDL restricted licence conditions (night-time and passenger), and crashes as a driver during the restricted licence stage. RESULTS: After controlling for other variables, factors independently associated with adolescent low compliance with GDL conditions were: low parental knowledge of conditions, parents' implementing few driving rules, adolescent vehicle ownership, and parent crash involvement. Factors independently associated with adolescents being a crash involved driver were: parents' actively delaying licensure, adolescent vehicle ownership, and parent crash involvement. CONCLUSION: There is increasing recognition of the importance of parental involvement in adolescent driving. The results show that parents are influential in determining adolescent compliance with GDL and risk of crash. Parents can have considerable positive influence on their adolescent's driving through ensuring compliance with the components of GDL, limiting vehicle ownership and by modelling safe driving behaviours.

Unsupervised driving by learner licence holders: associated characteristics and crash risk.

AIMS: To determine: (a) the association between socio-demographic, and behavioural factors and compliance with supervised driving condition as a learner licensed driver, (b) whether unsupervised driving as a learner licence holder was associated with elevated crash risk while holding a learner licence. STUDY DESIGN: The study population was the New Zealand Drivers Study (NZDS) cohort, a prospective cohort study designed to explore the relationship between a comprehensive range of driving and traffic safety related factors and subsequent traffic crashes and convictions among newly licensed drivers. RESULTS: Thirty-one percent of the study sample was non-compliant at least once with the supervised driving condition. Many socio-demographic and behavioural risk factors were independently associated with unsupervised driving. The strength of the associations was greatest for those with relatively high levels of unsupervised driving (13+ trips). High distance driven showed the strongest relationship: RR 8.91 (95% CI 5.27-15.07). Unsupervised driving was associated with increased risk of crash: 1-12 trips: RR 1.84 (1.29-2.61), and 13+ trips: RR 2.71 (1.94-3.80). Given that a significant portion of learner licence holders report driving unsupervised and those that violate this condition the most are more likely to crash, evaluation of strategies designed at improving compliance with learner licence supervised driving condition should be a research priority.

Reducing young driver crash casualties in Great Britain - use of routine police crash data to estimate the potential benefits of graduated driver licensing.

Crashes involving young drivers (YD) cause significant morbidity and mortality in Great Britain (GB). Graduated Driver Licensing (GDL) is used in some countries to address this. This study assessed potential casualty and cost savings of possible GDL programmes in GB. Police road crash data were analysed to identify YD crashes at night or while carrying passengers. These data were then used to estimate the potential effects of GDL. 314,561 casualties and 3469 fatalities occurred in YD crashes. 25.1% of YD crashes occurred between 9 pm and 6 am and 24.4% occurred with a 15- to 24-year old passenger in the car. A 'strict' form of GDL in GB (night time restriction 9 pm-6 am, no 15-24 year old passengers) with 50% compliance would prevent 114 deaths and 872 serious casualties each year. The estimated value of prevention is £424M pa. A 'less strict' form of GDL (night time restriction 10 pm-5 am, maximum of one 15-19 year old passenger) with 50% compliance would prevent 81 deaths and 538 serious injuries. The estimated value of prevention is £273M pa. Implementing GDL in GB could save significant numbers of lives. Public health organisations have a duty to advocate for such legislation.

Age, period and cohort effects on the incidence of motorcyclist casualties in traffic crashes.

OBJECTIVES: (1) Estimate age, period and cohort effects for motorcyclist traffic casualties 1979-2008 in New Zealand and (2) forecast the incidence of New Zealand motorcycle traffic casualties for the period 2019-2023 assuming future age, cohort and period effects, and compare these with an estimate based on simple linear extrapolation. METHODS: Age-period-cohort (APC) modelling was used to estimate the individual effects of age, period and cohort after adjusting for the other two factors. Forecasting was produced for three period-effect scenarios. RESULTS: After adjusting for cohort and period effects, 15-19-year-olds have substantially elevated risk. The period effect reduced in significance over time until the last period, 2004-2008, where the risk was higher than the preceding period. The 10-year cohorts born 1949-1958, 1954-1963, 1959-1968 and 1964-1973, had elevated risk. The forecasting, based on APC modelling, resulted in the lowest estimates of the future incidence being approximately one-third that of the highest estimate (6641). CONCLUSION: Trends in motorcycle casualties have been influenced by significant independent age, period and cohort effects. These need to be considered in forecasting future casualties. The selection of the period effect has a significant impact on the estimates. Which period-effect scenario readers choose to accept depends on their views about a wide range of factors which might influence motorcycle use and crash risk over time.

Validity of using linked hospital and police traffic crash records to analyse motorcycle injury crash characteristics.

Linking hospital discharge and police traffic crash records has been used to provide information on causes and outcomes for hospitalised traffic crash cases. Motorcyclists are particularly vulnerable to injury in a traffic crash, but no published linkage studies have reported in detail on this road user group. The present study examined motorcycle traffic crash injury cases in New Zealand in 2000-2004 by probabilistically linking national hospital discharge records with police traffic crash reports. Injury cases had to have spent at least one night in hospital before being discharged and were defined as serious or moderate based on their International Classification of Disease Injury Severity Scores (ICISS). Despite a robust linkage process, only 46% of cases could be linked to a police record; 60% of the serious injuries and 41% of the moderate. The low linkage was most likely due to under-reporting of crashes to or by the police. While moderate injury cases were expected to be under-reported, the level of under-reporting of cases with serious threat-to-life injuries is concerning. To assess whether the linked dataset could provide valid information on the crash circumstances and injury outcomes of hospitalised motorcycle crash cases, the characteristics of the linked and unlinked hospital discharge cases were compared using chi-square tests and multivariate logistic regression. Serious injury cases were less likely to be linked if only one vehicle was involved, or the injured riders and passengers were younger than 20 years or spent less than one week in hospital. For moderate injury cases, there were also differences in linkage by injured body region and crash month. While these discrepancies need to taken into consideration when interpreting results, the linked hospital-police dataset has the potential to provide insights into motorcycle crash circumstances and outcomes not otherwise obtainable.

Establishment of the New Zealand Drivers Study.

AIM: Despite a significant improvement since graduated licensing was introduced, traffic related injury remains the leading cause of death and hospitalisation among young New Zealanders. The New Zealand Drivers Study (NZDS) was established with a view to providing information that would lead to an improvement in this situation. The NZDS is a prospective cohort study designed to explore the relationship between a comprehensive range of driving and traffic safety related factors and subsequent traffic crashes and convictions among newly licensed drivers. We describe key process objectives in establishing the cohort, and our success in meeting them and the implications arising thereof. METHODS: We compare what occurred with what was proposed in the research protocol. RESULTS: We successfully established a cohort of 3992 newly licensed car drivers with substantial heterogenity in sociodemographic, behavioural, and driving experiences. We have 825 Maori that will allow us to undertake a separate Maori analyses. Response rates to interviews at the restricted and full licence stages have been very high at 87% and 93%, respectively. We have been successful via linkage in following them through the stages of licensure and via linkage obtaining national data on the outcomes of interest. CONCLUSIONS: The NZDS is well placed to make a significant contribution to our knowledge of young driver road safety behaviour. This process has already commenced.

Nonprogression through graduated driver licensing: characteristics, traffic offending, and reasons for nonprogression.

OBJECTIVES: In a graduated driver license environment, (1) compare nonprogressors with progressors in terms of prelearner license sociodemographic and behavioral factors, (2) determine whether nonprogressors were more likely to have had a traffic offense than progressors, and (3) determine why nonprogressors chose not to progress. METHODS: Our study population was that of the New Zealand Drivers Study (NZDS), a prospective cohort study of newly licensed drivers designed to explore the relationship between a comprehensive range of driving and traffic safety related factors and subsequent traffic crashes and convictions among newly licensed drivers. Nonprogressors, those who had not progressed from a learner to a restricted license 2 years after being eligible to do so, were compared with progressors in terms of their sociodemographic, behavioral characteristics, and traffic offense outcomes. RESULTS: Nonprogressors represented 38 percent of the cohort and had different sociodemographic and behavioral profiles than progressors. A delay in progression was associated with reduced risk of being a traffic offender. The primary reasons reported for nonprogression were too lazy or busy or limited access to the means to drive. CONCLUSION: Before restricting how long a novice driver can hold a learner license, as has been suggested by the Ministry of Transport, consideration should be given to the potential increased risk of offending once unsupervised driving is permitted.

The characteristics of young pre-licensed drivers: evidence from the New Zealand Drivers Study.

AIM: The aim of this study was to identify demographic and behavioural factors associated with pre-licensed driving. METHOD: A cohort comprising 3526 newly licensed drivers aged 15-24 years old from throughout New Zealand completed a questionnaire which sought information on pre-licensed driving behaviour and factors thought to be related to this. RESULTS: Almost half of the participants had driven on-road prior to passing their learner license theory test; 14% had driven more than 20 times; and 7.5% had driven more than 200 km. Multivariate logistic regression showed the results differed depending on the outcome examined. In general pre-licensed driving was significantly higher among males, among Maori, those living in a rural area, and those living in an area of high deprivation. Furthermore, those who drove pre-licensed were more likely to engage in other risky behaviours such as hazardous drinking and cannabis use, and have medium to high scores for sensation seeking and aggression/hostility. CONCLUSION: The young people who were pre-licensed drivers displayed a range of demographic and behavioural characteristics that indicate they may be at higher crash risk than their peers who did not drive before licensing. Identifying those who drive before licensing and targeting road safety interventions towards this group may help reduce the high crash risk among novice drivers.

Adolescent, and their parents, attitudes towards graduated driver licensing and subsequent risky driving and crashes in young adulthood.

PROBLEM: Although Graduated Driver Licensing Systems (GDLS) have helped reduce young driver crash rates, they remain significantly over-represented in crash statistics. To be effective GDLS rely heavily on support for the legislation by those directly involved; parents to enforce the restrictions and adolescents to comply. There is some evidence that practices regarding GDLS restrictions influence adolescent driving outcomes in the early stage of licensure. However there has been no examination undertaken on the influence of parent and adolescent attitudes toward GDLS on adolescents' driving behavior and crash experiences as they move into their young adult years. The aim of this research was to examine these relationships. METHOD: This investigation was based on a longitudinal study of a birth cohort, and uses data collected when the cohort members were aged 15, 18, and 21years. At age 15 both adolescent and their parent attitudes toward GDLS were measured. At age 18 adolescent GDLS attitudes were measured again. The association between these measures and self-reported risky driving behavior and crash involvement at age 21 were examined. RESULTS: Negative attitudes toward the learner supervisor restriction for males, and negative attitudes toward a GDLS for females were strongly associated with risky driving and crash involvement as young adults. IMPACT ON INDUSTRY: Targeting interventions to improve adolescents and parents understanding of the reasons for graduated licensing and the specific restrictions may improve attitudes and views and thereby contribute to a reduction in risky driving behaviors and crash risk among young adults.

Unlicensed driving among urban and rural Maori drivers: New Zealand drivers study.

OBJECTIVE: To determine the extent and type of self-reported unlicensed car driving and reasons given for driving before getting a license among Maori drivers in urban and rural areas of New Zealand. METHOD: Participants included 824 people of self-identified Maori ethnicity. The ages ranged from 15 to 65 years, with the majority of participants aged 15 (37%), 16 (21%), or 17 (14%) years at the time of recruitment. Participants were recruited after passing the car driver's learner license theory test at a driver licensing agency or a learner license course or by the participant responding to a postcard placed at licensing agencies nationwide. All participants completed a self-administered questionnaire that included items for a wide range of personal, driving, and licensing-related variables. The cohort was not randomly selected but included as many eligible participants as possible, with recruitment taking place in urban and rural areas of both the North and South Islands of New Zealand. RESULTS: Unlicensed car driving experience was common, especially among rural participants (urban: 65%, rural: 83%). The nature and extent of driving experience and reasons for driving unlicensed were remarkably similar for urban and rural drivers, Females (47%) were more likely than males (37%) to report previous experience of a serious traffic crash. Being stopped by the police for driving unlicensed was not common (24% urban, 17% rural), but for those who had been stopped, the consequences varied by residential location. CONCLUSIONS: Driving before obtaining a driver's license was common practice and the amount of driving extensive, for both rural and urban drivers. Furthermore, contrary to common perceptions in New Zealand, the need and opportunities for driving were similar, irrespective of place of residence. This suggests that similar issues may need to be addressed by both urban and rural Maori community road safety providers.

A critical examination of the arguments against raising the car driver licensing age in New Zealand.

OBJECTIVES: In 1987, to address an increasing problem of injury among young drivers, New Zealand chose a graduated driver licensing system (GDLS), in preference to raising the minimum car driver licensing age. Since 1987 the GDLS has contributed to a significant reduction in young driver injury, but a recent spate of high-profile crashes has raised public concern about young drivers and road safety. In response to this concern, a bill has been introduced into the parliament to increase the minimum driver licensing age from 15 to 16 years. In this article we critically examine some of the arguments against raising the licensing age. Our motivation for doing this is that many of the arguments against raising the driver's license age, though they have high face validity, are often presented without any supporting evidence. METHOD: Our sources for argument include Hansard (New Zealand parliament's official record), various public media, various agencies Web sites, census data, and published papers. The arguments examined against raising the age were the impact on the mobility of 15- and 16-year-olds, disadvantage to the rural sector, alternative transport options, increasing the age shifts the problem, changing the law will not change young driver behaviors, changing the law will not fix the problem, and education is the answer. RESULTS: For each of the topics available, data were examined to quantify the extent to which these factors would affect young drivers if the minimum driver licensing age was raised to 16 years. CONCLUSION: The evidence demonstrates that young age, independent of experience, is a major determinant of risk; therefore, raising the minimum licensing age would have safety benefits. We also show that many of the arguments against raising the age are based on either no evidence or misinformation. Though raising the licensing age would to some extent disadvantage the rural sector, it may also be in the rural sector where the greatest gains in crash reduction are made.

The utility of routinely collected data in evaluating important policy changes: the New Zealand alcohol purchasing age limit example.

We used the recent lowering of the alcohol purchasing age in New Zealand to examine the proposition that routinely collected data are often insufficient in evaluating important policy changes. We estimated prechange and postchange incidence rate ratios for actual and hypothetical population sizes and hospital admissions related to alcohol poisoning and assaults. Even with a hypothetical youth population 10 times larger than New Zealand's actual youth population, comparisons were underpowered because there were too few observations. Governments should use the enactment of health legislation as an opportunity to build the research evidence base by ensuring that evaluations are initiated in advance.

The opinions of newly licensed drivers in New Zealand on the minimum car driver licensing age and reasons for getting a licence.

AIM: To investigate the opinions of newly licensed drivers towards the minimum age of car driver licensing, and reasons for getting a licence. METHOD: The New Zealand Drivers Study (NZDS) is a prospective cohort study of 3992 newly licensed car drivers in New Zealand, recruited between 1 February 2006 and 31 January 2008 from driver licensing agencies and licensing courses throughout New Zealand. The cohort comprises 51% females and 49% males, 49% were aged 15 years and 28% 16-17 years, 55% self-identified as New Zealand European, 21% Maori, 13% Pacific, 11% Asian, and 15% as "other". After passing the learner licence theory test all participants completed a questionnaire that included a range of questions on driver licensing topics, including minimum driver licence age and reasons for getting a car driver's licence. RESULTS: Overall, 51% of newly licensed drivers supported 15 years as the minimum age to start licensing but this varied significantly by the age, gender, and residential location of the learner driver. The most frequently reported reason for getting a licence related to independence and freedom. This applied equally to males and females, rural and urban drivers, and across all ages, although for learner drivers aged 18+ years, to drive to work was also a very important reason for having a licence. CONCLUSION: Contrary to what many may believe to be the case, the evidence presented here showed that there was not universal opposition by young people to raising the driver licensing age. Also those in rural and urban areas had much in common with respect to the reasons for obtaining a licence. With respect to the latter it is worth noting that travel for work was of most relevance to the learner drivers aged 18 years or older. Overall, these findings suggest that increasing the minimum age for licensing would have relatively little impact on essential travel among young people in New Zealand.

A longitudinal examination of the relationship between adolescent problem behaviors and traffic crash involvement during young adulthood.

Previous research examining the relationship between adolescent problem behaviors and young adult traffic outcomes (crashes, convictions, risky driving) has produced differing results. Possible reasons for this may be the heterogeneity of the crash outcomes (from minor fender-benders to fatal crashes), the gender of the driver, and/or the age of the driver. The aim of this research was to investigate the relationship between adolescent problem behaviors and young adult crashes to determine the extent to which the above factors influenced this relationship. This study was part of the Dunedin Multidisciplinary Health and Development Study (DMHDS), which is a longitudinal study of a cohort (n = 1,037) born in Dunedin, New Zealand, from April 1972 to March 1973. This cohort has been followed up regularly since birth, and the data for the present research were obtained at the 18-, 21-, and 26-year-old follow-up interviews. The problem behaviors examined were those identified by Jessor in the theory of problem behavior, namely, tobacco smoking, marijuana use, alcohol use, delinquent behavior, and unsafe sexual behavior. Data for these measures were obtained in personal interviews when the cohort was aged 18 years. The self-reported crash data were obtained at the age 21 and age 26 follow-up interviews. Driving exposure, academic qualifications, employment, being a parent, and marital status were included as potential confounders. The results show that involvement in adolescent problem behaviors predicted crash involvement at age 21 for the females but not the males and at age 26 for the males but not the females. Possible explanations for these differences by age and gender are discussed.

Personality factors as predictors of persistent risky driving behavior and crash involvement among young adults.

OBJECTIVES: The aim of this study was to examine the relationship between personality factors assessed during adolescence and persistent risky driving behavior and traffic crash involvement among young adults. DESIGN: Data for this investigation were drawn from the Dunedin Multidisciplinary Health and Development Study, a longitudinal study of a cohort born in Dunedin, New Zealand. SUBJECTS: The study population was 1037 young people born between 1 April 1972 and 31 March 1973. MAIN OUTCOME MEASURES: The main outcome measures were persistent risky driving behaviors and crash involvement, collected in a face-to-face road-safety interview at ages 21 and 26. RESULTS: The only outcomes for which there were sufficient numbers of females were a driver involved in any crash and a driver involved in an injury crash. Univariate logistic regression revealed that there were no significant predictors for either of these outcomes. For the males, at the univariate level, aggression, traditionalism, and alienation were the personality scales most frequently associated with risky driving behavior and crash risk. After adjusting for driving exposure, only high levels of aggression predicted being a driver involved in a crash, and alienation predicted being a driver involved in an injury crash. CONCLUSION: These results suggest that road-safety interventions seeking to deter young adult males from persistent risky driving behavior need to be directed at those who do not endorse traditional views, are aggressive, and feel alienated from the rest of society.

Minimum purchasing age for alcohol and traffic crash injuries among 15- to 19-year-olds in New Zealand.

OBJECTIVES: In 1999, New Zealand lowered the minimum purchasing age for alcohol from 20 to 18 years. We tested the hypothesis that this increased traffic crash injuries among 15- to 19-year-olds. METHODS: Poisson regression was used to compute incidence rate ratios for the after to before incidence of alcohol-involved crashes and hospitalized injuries among 18- to 19-year-olds and 15- to 17-year-olds (20- to 24-year-olds were the reference). RESULTS: Among young men, the ratio of the alcohol-involved crash rate after the law change to the period before was 12% larger (95% confidence interval [CI]=1.00, 1.25) for 18- to 19-year-olds and 14% larger (95% CI=1.01, 1.30) for 15- to 17-year-olds, relative to 20- to 24-year-olds. Among young women, the equivalent ratios were 51% larger (95% CI=1.17, 1.94) for 18- to 19-year-olds and 24% larger (95% CI=0.96, 1.59) for 15- to 17-year-olds. A similar pattern was observed for hospitalized injuries. CONCLUSIONS: Significantly more alcohol-involved crashes occurred among 15-to 19-year-olds than would have occurred had the purchase age not been reduced to 18 years. The effect size for 18- to 19-year-olds is remarkable given the legal exceptions to the pre-1999 law and its poor enforcement.