Lee-hwa Chen

Fragility versus excessive crash involvement as determinants of high death rates per vehicle-mile of travel among older drivers

Using multiple national data systems, the roles of fragility (susceptibility to injury) versus excessive crash involvement in the increased fatality risk of older drivers per vehicle-mile of travel (VMT) were estimated. For each age and gender group, deaths per driver involved in a crash (a marker of fragility) and drivers involved in crashes per VMT (a marker of excessive crash involvement) were computed. Compared with drivers ages 30-59, those younger than 20 and those 75 or older both had much higher driver death rates per VMT. The highest death rates per mile driven, 13-fold increases, were observed among drivers age 80 or older, who also had the highest death rates per crash. Fragility began to increase at ages 60-64 and increased steadily with advancing age, accounting for about 60-95% of the excess death rates per VMT in older drivers, depending on age group and gender. Among older drivers, marked excesses in crash involvement did not begin until age 75, but explained no more than about 30-45% of the elevated risk in this group of drivers; excessive crashes explained less of the risk among drivers ages 60-74. In contrast, crash over-involvement was the major factor contributing to the high risk of death among drivers younger than 20, accounting for more than 95% of their elevated death rates per VMT. Although both fragility and crash over-involvement contributed to the excess death rates among older drivers per VMT, fragility appeared to be of over-riding importance. These findings suggest that measures to improve the protection of older vehicle occupants in crashes should be vigorously pursued.

Graduated Driver Licensing Programs and Fatal Crashes of 16-Year-Old Drivers: A National Evaluation

CONTEXT. Implementation of graduated driver licensing programs is associated with reductions in crash rates of young drivers, but graduated driver licensing programs vary in their components. The impact of programs with different components is unknown. OBJECTIVE. The purpose of this work was to determine which graduated driver licensing programs are associated with the greatest reductions in fatal motor vehicle crashes involving 16-year-old drivers. METHODS. We conducted a retrospective study of all 16-year-old drivers involved in fatal crashes in the United States from 1994 through 2004 using data from the Fatality Analysis Reporting System and the US Census Bureau. We measured incidence rate ratios of fatal motor vehicle crashes involving 16-year-old drivers according to graduated driver licensing programs, adjusted for state and year. RESULTS. Compared with state quarters with no graduated driver licensing program components, reductions of 16% to 21% in fatal crash involvement rates of 16-year-old drivers occurred with programs that included ≥3-month mandatory waiting period, nighttime driving restriction, and either ≥30 hours of supervised driving or passenger restriction. Reductions of 18% to 21% occurred in state quarters with programs that included ≥5 of the 7 components examined. Drivers aged 20 to 24 or 25 to 29 years did not experience significant reductions. CONCLUSION. Comprehensive graduated driver licensing programs are associated with reductions of ∼20% in 16-year-old drivers’ fatal crash involvement rates. The greatest benefit seems to be associated with programs that include age requirements and ≥3 months of waiting before the intermediate stage, nighttime driving restriction, and either ≥30 hours of supervised driving or passenger restriction.

Validity of self reported home safety practices

Objectives: To examine the validity of self reported data on parents’ home safety practices of using smoke alarms and stair gates, and having syrup of ipecac. Setting: Families from a pediatric continuity clinic in a large, urban teaching hospital with infants from birth to 6 months were enrolled in the study. Methods: As part of a randomized controlled trial to promote home safety, parents’ responses to personal interviews were compared to observations made in the respondents’ homes two to four weeks after the interview. Positive and negative predictive values, sensitivity, and specificity were computed and compared between the intervention and control group families. Results: Sensitivities were high among the four safety practices. Specificities were much lower and fell into a much wider range than sensitivities. The positive predictive values were low and the negative predictive values were high. No differences in these indicators of validity were found between intervention and control group families. Conclusions: If the main interest in an evaluation is on the relative difference between study groups, rather than the absolute value of the outcome measure, our results suggest that self reported data may be of acceptable validity. However, when assessing a patient’s risk, clinicians need to recognize the problem of over-reporting of safety practices.

Drinking histories of fatally injured drivers.

Context: About 30% of drivers killed in crashes have high blood alcohol concentrations (BACs) of 0.10+ g/dl. There is a question about whether these drivers primarily are problem drinkers who chronically drink and drive—the so-called hard core drinking drivers. Objective: To investigate drinking histories of fatally injured drivers in relation to their BACs. Design and participants: Retrospective cohort study of 818 fatally injured drivers who were included in the 1993 National Mortality Followback Survey (a national sample of US deaths in which next of kin were interviewed) and whose BACs were recorded by the Fatality Analysis Reporting System, a census of US traffic deaths. Main outcome measure: Problem drinking indicators. Results: At least one indicator of potential problem drinking, primarily heavy drinking, was reported for 68% of drivers with very high BACs (0.15+ g/dl), 41% with BACs of 0.10–0.14 g/dl, 32% with BACs of 0.01–0.09 g/dl, and 7% with zero BACs. Spouses provided more credible responses than other relatives: they were more likely to report at least occasional drinking and driving among deceased drivers with high BACs. For the most direct signs of problem drinking (described as a problem drinker during the last month of life or frequently driving after having five or more drinks), spousal reports suggested the prevalence of problem drinking among drivers with very high BACs was 22% (having both indicators), 32% (frequently driving after having five or more drinks), 44% (described as problem drinker), or 57% (having either indicator). Conclusions: Drivers with BACs of 0.10+ g/dl were far more likely than sober drivers to be described as having markers of problem drinking. However, many did not have indicators suggestive of problem drinking. In addition to programs focused on repeat offenders or problem drinkers, countermeasures such as sobriety checkpoints that target a broader spectrum of drinking drivers are appropriate.

Potential benefits of restrictions on the transport of teenage passengers by 16 and 17 year old drivers

Objectives—The presence of passengers is associated with fatal motor vehicle crashes of teenage drivers. A restriction against newly licensed teenage drivers carrying passengers has been included in some, but not all, graduated licensing systems. The purpose of this study was to predict the net effects on all types of road users, including vehicle occupants and non-occupants, of possible prohibitions against 16–17 year old drivers carrying passengers. Methods—Two national datasets, a census of fatal crashes and a sample of trips in the United States, were used to compute 1995 road user death rates. Potential effects of restrictions on drivers ages 16–17 carrying passengers younger than 20 were estimated, based on road user death rates and potential choices made by passengers who would have traveled with 16–17 year old drivers if there were no restrictions. Results—There were 1181 road user deaths in 1995 involving drivers ages 16–17 whose passengers were all younger than age 20. The predicted number of lives in the United States that would be saved annually ranges from 83 to 493 (corresponding to reductions of 7–42% in road user deaths) for drivers ages 16 and 17 combined. Similar percentages of reductions (8–44%) were predicted solely for 16 year old drivers. Assuming passenger restrictions would apply to all 16 year old drivers and at least one third of 17 year old drivers, an estimated 60–344 fewer deaths per year may occur if restrictions are mandated. Conclusions—Restrictions on carrying passengers younger than 20 should be considered for inclusion in graduated licensing systems. Even if fewer than half the drivers obey the restrictions, a substantial reduction in road user deaths would be expected. Further evaluation based on real world experience is needed to confirm their efficacy.