The relationship between blood alcohol concentration (BAC), age, and crash risk

The effects of minimum legal drinking age 21 laws on alcohol-related driving in the United States

OBJECTIVE

To examine trends in alcohol consumption and alcohol-related crashes among people younger than 21 in the United States and to review evidence on the effects of minimum legal drinking age (MLDA) laws.

METHODS

Trends in alcohol-related crashes and alcohol consumption among young people were examined, and studies on the effects of lowering and raising the drinking age were reviewed.

RESULTS

MLDA laws underwent many changes during the 20th century in the United States. Since July 1988, the MLDA has been 21 in all 50 states and the District of Columbia. Surveys tracking alcohol consumption among high school students and young adults found that drinking declined since the late 1970 s, and most of the decline occurred by the early 1990 s. These were the years when states were establishing, or reinstating, a MLDA-21. Among fatally injured drivers ages 16-20, the percentage with positive BACs declined from 61% in 1982 to 31% in 1995, a bigger decline than for older age groups; declines occurred among the ages directly affected by raising MLDAs (ages 18-20) and among young teenagers not directly affected (ages 16-17). Almost all studies designed specifically to gauge the effects of drinking age changes show MLDAs of 21 reduce drinking, problematic drinking, drinking and driving, and alcohol-related crashes among young people. Yet many underage people still drink, many drink and drive, and alcohol remains an important risk factor in serious crashes of young drivers, especially as they progress through the teenage years. Stepped-up enforcement of MLDA and drinking and driving laws can reduce underage drinking. Recent efforts to lower MLDAs to 18 and issue licenses to drink upon completion of alcohol education have gained local and national media attention. There is no evidence that alcohol education can even partially replace the effect of MLDA-21.

CONCLUSIONS

The cause and effect relationship between MLDAs of 21 and reductions in highway crashes is clear. Initiatives to lower the drinking age to 18 ignore the demonstrated public health benefits of MLDAs of 21.

IMPACT ON INDUSTRY

Lowering the drinking age to 18 will increase highway crash deaths among young people.

Poverty as a determinant of young drivers' fatal crash risks

PROBLEM

U.S. teenaged and young-adult drivers' elevated rates of fatal traffic crash involvement typically are attributed to biological and developmental risk-taking associated with young age. However, young drivers differ from older ones along several sociodemographic dimensions, including higher poverty rates and greater concentration in poorer areas, which may contribute to their risks.

METHOD

Using Fatality Analysis Reporting System, Census, and Federal Highway Administration data for 1994-2007, bivariate and multivariate regression analyses were conducted of fatal motor-vehicle crash involvements per 100 million miles driven by driver age (16 through 74) and state along with 14 driver-, vehicle-, and state-level variables.

RESULTS

Driver age was not a significant predictor of fatal crash risk once several factors associated with high poverty status (more occupants per vehicle, smaller vehicle size, older vehicle age, lower state per-capita income, lower state population density, more motor-vehicle driving, and lower education levels) were controlled. These risk factors were significantly associated with each other and with higher crash involvement among adult drivers as well.

SUMMARY AND DISCUSSION

The strong association between fatal crash risk and environments of poverty as operationalized by substandard vehicle and driving conditions suggests a major overlooked traffic safety factor particularly affecting young drivers.

The effects of drink-driving checkpoints on crashes--a meta-analysis

A meta-analysis has been conducted on the effects on crashes of DUI-checkpoints (DUI, driving under the influence). The results indicate that crashes involving alcohol are reduced by 17% at a minimum and that all crashes, independent of alcohol involvement, are reduced by about 10-15%. In a moderator analysis the effects of a number of factors that may affect the effectiveness of DUI-checkpoints were investigated by means of subgroup analyses and meta-regression. Those moderator variables that were found to be most relevant, are the time period studied, country, and study design. DUI-checkpoints were found to be most effective during the first half year. Australian checkpoints were found to be more effective than checkpoints in other countries. Smaller crash reductions were found in studies that have applied a control group than in other studies. Testing all drivers who are stopped at a checkpoint may improve the effectiveness of DUI-checkpoints. The results do not indicate that DUI-checkpoints have greater effects on more severe crashes or that the use of paid publicity improves the effectiveness. Most likely there are further factors that affect the effectiveness of DUI-checkpoints that could not be investigated in the present analysis.

The Long Beach/Fort Lauderdale relative risk study

PROBLEM

The role of alcohol as a major factor in traffic crash causation has been firmly established. However, controversy remains as to the precise shape of the relative risk function and the BAC at which crash risk begins to increase.

METHODS

This study used a case-control design in two locations: Long Beach, California, and Fort Lauderdale, Florida. Data were collected on 2,871 crashes of all severities and a matched control group of drivers selected from the same time, location, and direction of travel as the crash drivers. Of the 14,985 sample drivers, 81.3% of the crash drivers and 97.9% of the controls provided a valid BAC specimen.

RESULTS

When adjusted for covariates and nonparticipation bias, increases in relative risk were observed at BACs of .04-.05, and the elevations in risk became very pronounced when BACs exceeded .10.

DISCUSSION

The results provide strong support for .08 per se laws and for state policies that increase sanctions for BACs in excess of .15.

IMPACT ON INDUSTRY

This study provides further precision on the deleterious effects of alcohol on driving and, by implication, on other complex tasks.