Association of Alcohol-related Laws with Deaths due to Motor Vehicle and Motorcycle Crashes in the United States, 1980–1997

Andrés Villaveces1,2,, Peter Cummings1,2, Thomas D. Koepsell1,2,3, Frederick P. Rivara1,2,4, Thomas Lumley5 and John Moffat6

1 Department of Epidemiology, School of Public Health and Community Medicine, University of Washington, Seattle, WA.
2 Harborview Injury Prevention and Research Center, University of Washington, Seattle, WA.
3 Department of Health Services, School of Public Health and Community Medicine, University of Washington, Seattle, WA.
4 Department of Pediatrics, School of Medicine, University of Washington, Seattle, WA.
5 Department of Biostatistics, School of Public Health and Community Medicine, University of Washington, Seattle, WA.
6 Washington Traffic Safety Commission, Olympia, WA.

Received for publication May 31, 2002; accepted for publication August 7, 2002.


    ABSTRACT
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The authors compared US motor vehicle and motorcycle mortality rates during periods when each of several alcohol-related laws were in effect with mortality rates during other periods. During the period 1980–1997, there were 792,184 deaths due to motor vehicle crashes and 63,052 deaths due to motorcycle crashes. An estimated 26% and 49% of these fatalities, respectively, were attributable to alcohol use. The incidence of alcohol-related mortality in motor vehicle crashes was lower when laws specifying a blood alcohol concentration of 0.08 g/dl per se (laws stating that it is a criminal offense to drive with a blood alcohol concentration above the state’s legal limit) were in effect (adjusted rate ratio (RR) = 0.86, 95% confidence interval (CI): 0.83, 0.88). For motorcycle deaths, the adjusted rate ratio was 0.87 (95% CI: 0.79, 0.95). The incidence of alcohol-related mortality in motor vehicle crashes was also lower during periods when two other types of laws were in effect: zero tolerance laws (adjusted RR = 0.88, 95% CI: 0.86, 0.90) and administrative license revocation laws (adjusted RR = 0.95, 95% CI: 0.93, 0.98). Overall motorcycle mortality was lower when administrative license revocation laws were in effect (adjusted RR = 0.95, 95% CI: 0.92, 0.98).

accidents, traffic; alcoholic intoxication; automobile driving; automobiles; legislation; motorcycles

Abbreviations: Abbreviations: BAC, blood alcohol concentration; CI, confidence interval; RR, rate ratio.


    INTRODUCTION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
In 1998, 15,935 motor vehicle fatalities in the United States were attributed by the National Highway Traffic Safety Administration to alcohol use (1). Approximately 43 percent of all fatal motorcycle crashes in the United States involve alcohol (2), and motorcycle drivers have the highest frequency of alcohol use among all motor vehicle drivers (3). Motorcycle riders who have been consuming alcohol wear helmets half as often as sober riders (4). Unhelmeted riders are twice as likely to incur a head injury of any type and are at least three times more likely to incur a fatal head injury (5).

In the United States, many states have passed laws aimed at drinking and driving. Several studies have examined these laws individually, usually in a single state or a few states (613). In some studies, other laws concurrently in effect have not been included in the analysis as potential confounders (611, 14). With regard to motorcycle riders, while several studies have found an association between helmet laws and motorcycle deaths (1521), few have studied alcohol legislation (22, 23). To our knowledge, no study has evaluated potential interactions between different legal measures.

We estimated the association between several laws pertaining to driving under the influence of alcohol and crash mortality. We studied the following policies simultaneously: 1) the effect of laws making a blood alcohol concentration (BAC) of 0.08 g/dl per se illegal (laws which state that it is a criminal offense to drive with a BAC above the state’s legal limit), as compared with any higher legal limits or no legal limit; 2) the effect of having a BAC illegal limit of 0.02 g/dl or less for persons younger than age 21 years (zero tolerance laws); 3) the effect of having administrative license revocation laws; 4) the effect of explicitly allowing police to set up sobriety checkpoints; and 5) the effect of imposing mandatory jail terms after a first conviction for driving under the influence of alcohol. We also considered, as potentially confounding factors, primary and secondary seat-belt laws (the former allow police to stop and ticket an occupant solely because he or she is unrestrained; the latter allow police to issue a citation for lack of restraint use only if the motorist has been stopped for some other reason), universal helmet laws (which mandate that all motorcycle riders wear a helmet), and selective helmet laws (which mandate helmet use for younger persons, defined as motorcycle riders younger than age 20, 18, or 16 years, depending on the state).


    MATERIALS AND METHODS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Mortality data
We used crash mortality data for the United States for the period 1980–1997. We obtained counts of motor vehicle and motorcycle crash deaths by year, state, type of vehicle, sex, and age from the Fatality Analysis Reporting System (24). This database provides information on driver and occupant/rider characteristics, vehicle characteristics, and the circumstances surrounding all crashes that involve a death within 30 days of the incident.

Denominator data
Population estimates by year, state, age, and sex were downloaded from the US Census Bureau website (25). We also obtained data on total vehicle miles of travel by year and number of registered motorcycles by state and year from the Federal Highway Administration (26).

Legal data
Information on the date on which each law went into effect was obtained by reviewing the statutes of each state for the period 1980–1997. This was compared with the dates on law lists provided by the National Highway Traffic Safety Administration (2732). Any disagreement between these sources was resolved by reviewing multiple versions of the Digest of State Alcohol-Related Legislation (33).

Analysis
Separate analyses were conducted using both person-time and annual miles driven as the denominators for rate ratios. We assessed the effects of the laws using three outcome measures: 1) counts of all deaths due to motor vehicle crashes, including pedestrian and bicycle deaths; 2) counts of deaths due to automobile crashes only, excluding pedestrians and bicyclists and crashes of heavy trucks, buses, and motorcycles; and 3) counts of all motorcycle deaths. We assessed zero tolerance laws by restricting the population denominator and counts of deaths to persons younger than age 21 years, because these laws apply specifically to this population. Using the same rationale for selective helmet laws, we assessed the effect of these measures among persons younger than age 16 years. We assessed both sex and age (categorized as 0–11, 12–20, 21–29, 30–39, 40–49, 50–59, and >=60 years) as potential confounders but ultimately did not adjust for these variables, since the slight changes in the age and sex distribution of the population over time did not change any rate ratio estimates by more than 0.02. We studied the potential multiplicative effects of every combination of the five alcohol-related laws.

The study period of 18 years, multiplied by the 51 states (including the District of Columbia), can be thought of as 918 state-years. The number of state-years when relevant laws were in effect ranged from 81.9 for BAC laws to 412.4 for selective helmet laws. For each law, we estimated the mortality rate ratio for periods with a law compared with other periods, adjusted for the presence of the other alcohol-related laws, seat-belt laws, and any trends in crash mortality over time.

We used random-effects Poisson regression models for longitudinal data and estimated mortality rate ratios conditional on state (34) for each law, using Stata 6.0 software (35). For each law, the resulting rate ratio was a pooled estimate of the within-state ratio of mortality rates while the law was in effect, compared with what would have been expected in those same states had the law not been implemented. Because mortality counts over time can be correlated within a state, we used a variance estimator that accounted for possible within-state correlation. We used a random-effects model, which accounts, in a statistical sense, for the possibility that the effects of a law may differ between states. To control for any trend in traffic mortality rates, we divided time into 18 consecutive 1-year segments and included these variables in the models by using linear spline terms.

Alcohol-related deaths
We estimated the number of deaths that could be attributed to alcohol use by a driver, since it is these deaths that alcohol-related laws were designed to prevent. We calculated attributable fractions (36) ((relative risk – 1)/relative risk) on the basis of the BAC of the intoxicated driver and applied them to all individuals who died in that event. These calculations were based on reported tables of the relative risk of driver involvement in fatal crashes due to alcohol in relation to age and sex (37). For example, suppose that 10 38-year-old male drivers with a BAC of 0.09 g/dl were each involved in a single-vehicle crash, where one person died in each crash. According to the tables by Zador et al. (37), they each had a relative risk of involvement of 8.58 compared with not being intoxicated. The number of deaths attributable to alcohol for those specific events would be 8.83 (([(8.58 – 1)/8.58]) x 10 deaths = 8.83).

For those few crashes in which two or more drivers had positive BACs, we computed a pooled attributable fraction; the attributable fraction for driver 1 (AF1) was pooled with the attributable fraction for driver 2 (AF2) as AFpooled = 1 – ((1 AF1) x (1 – AF2)). The pooled value was then applied to all fatalities in that crash. Zador et al. (37) estimated a few relative risks below 1.0 for some age groups; for these few crashes, we assigned an attributable fraction of 0.1 to all fatalities. We thought it was implausible that subjects with a positive BAC would be less likely to be involved in a crash or fatal event than sober persons (38).

BACs were missing for 60 percent of drivers. We therefore used multiple imputation methods (3942), described in detail by Rubin et al. (43), for the imputation of BACs in the Fatality Analysis Reporting System data. The models used police-reported drinking, age, sex, use of a restraint system, driver’s license status, injury severity, previous infractions, day of the week, time of day, vehicle’s role in the crash, vehicle class, and vehicle’s position on the roadway as predictors of BAC values (44). The first imputation step assigned each driver to either no alcohol use or any alcohol use. The second step imputed the BACs among drivers who were predicted to have any level of alcohol in their bloodstream. Both steps used an expectation-maximization algorithm and a Markov-chain Monte Carlo method for simulating the draws from the cell probabilities (41). We used software written for S-Plus by Schafer (45, 46). We generated 10 complete data sets which differed, one from another, on the imputed BAC values and consequently on the estimated count of deaths attributable to alcohol.

For example, a 25-year-old automobile driver with a missing BAC value could be assigned three times to no alcohol value and seven times to some positive value. In the three data sets with a BAC assigned to 0.0, this driver’s crash would contribute no deaths related to alcohol use. In the data sets with the BAC assigned to some value greater than 0, this driver’s crash would contribute to the count of alcohol-related deaths. The final count of deaths attributable to alcohol is an average of the alcohol-related counts in each of the 10 imputed data sets.

We then carried out Poisson regression as described above, producing 10 estimates for the effects of each law. We combined these estimates for each variable by averaging them on a logarithmic scale. Confidence limits were computed using methods that account for both the variance within each imputed data set and the variance between the 10 imputed data sets (41).


    RESULTS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
During the period 1980–1997, there were 792,184 deaths due to traffic crashes in the United States (table 1). For all crashes, 68 percent of the dead were male, the median age of the dead was 28 years, and 26 percent of the deaths were attributable to alcohol use. Seventy-one percent of the deaths (n = 560,944) occurred to occupants in automobiles, and 31 percent of these were due to alcohol (table 2).


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TABLE 1. Mortality rates for all motor vehicle fatalities, by period of law enactment, United States, 1980–1997
 

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TABLE 2. Mortality rates for automobile fatalities, by period of law enactment, United States, 1980–1997
 
There were 63,052 deaths due to motorcycle crashes (table 3). Ninety percent of the dead were male, and 61 percent were between ages of 21 and 39 years. An estimated 31,005 motorcycle deaths (49 percent) were attributable to alcohol use (table 3).


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TABLE 3. Mortality rates for motorcycle fatalities, by period of law enactment, United States, 1980–1997
 
In the discussion below, the denominator was person-years unless otherwise stated, and all mortality rate ratios were adjusted as described in Materials and Methods.

BAC 0.08 g/dl laws
During time periods when a state had a BAC standard of 0.08 g/dl as an indication that the driver was legally intoxicated, compared with periods with a higher BAC standard or no standard, the incidence of all crash fatalities was lower (rate ratio (RR) = 0.97, 95 percent confidence interval (CI): 0.96, 0.98). The association between the law and mortality was stronger among all alcohol-related deaths (table 4). Results were essentially the same when the number of miles driven was used as the denominator and when the analysis was limited to deaths occurring in automobiles. When time periods with a BAC standard of 0.08 g/dl were compared with time periods with a standard of 1.0 g/dl, the rate ratio was 0.97 (95 percent CI: 0.95, 0.98) for all deaths and 0.85 (95 percent CI: 0.83, 0.86) for alcohol-related deaths.


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TABLE 4. Adjusted mortality rate ratios* for motor vehicle fatalities calculated using person-years as the denominator for rates, United States, 1980–1997
 
For motorcycles, the adjusted rate ratio was 0.95 (95 percent CI: 0.91, 1.00). The association between these laws and mortality was stronger for alcohol-related deaths (table 5). The rate ratio was 0.92 (95 percent CI: 0.88, 0.97) for all motorcycle crash fatalities and 0.85 (95 percent CI: 0.77, 0.94) for alcohol-related motorcycle deaths using number of registered motorcycles as the denominator (table 5).


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TABLE 5. Adjusted mortality rate ratios* for motorcycle fatalities, United States, 1980–1997
 
Zero tolerance laws
During periods with a law that forbade drivers younger than 21 years to have any alcohol in their blood or limited the BAC to less than 0.02 g/dl, compared with periods with a higher BAC standard or no standard for drivers under age 21 years, crash mortality was lower (RR = 0.96, 95 percent CI: 0.95, 0.97). We found a stronger association between these laws and alcohol-related deaths (table 4). This association was stronger among persons under age 21 years: The rate ratio was 0.94 (95 percent CI: 0.92, 0.96) for all deaths and 0.83 (95 percent CI: 0.76, 0.90) for deaths attributed to alcohol.

These laws were not associated with rates of motorcycle death (table 5). The results were similar when we used registered motorcycles as the denominator or examined alcohol-related crashes. For the analysis restricted to persons under age 21 years, there were 732 deaths during periods when the law was in effect (rate = 0.11 per 100,000 person-years) and 13,983 deaths when the law was not in effect (rate = 0.37 per 100,000 person-years) (RR = 0.91, 95 percent CI: 0.82, 1.01). For the same subpopulation, there were 124 alcohol-related deaths during periods when the law was in effect (rate = 0.02 per 100,000 person-years) and 3,567 alcohol-related deaths during other periods (rate = 0.01 per 100,000 person-years) (RR = 0.91, 95 percent CI: 0.66, 1.27).

Administrative license revocation laws
When a state had a law that quickly revoked a driver’s license if the BAC was higher than legally allowed, the incidence of all crash fatalities was lower (RR = 0.95, 95 percent CI: 0.94, 0.96). We found similar associations between these laws and mortality when we examined all alcohol-related deaths, when we limited the analysis to deaths occurring in automobiles, and when we used vehicle miles as the denominator.

The incidence of motorcycle crash fatalities was also lower with this type of law (RR = 0.95, 95 percent CI: 0.92, 0.98). We found no association when we used number of registered motorcycles as the denominator. We found weak associations between these laws and alcohol-related motorcycle deaths (table 5).

Sobriety checkpoint laws
When a law that allowed the use of sobriety checkpoints was in force, the incidence of all crash fatalities was slightly greater (RR = 1.02, 95 percent CI: 1.01, 1.03). Similar results were obtained for deaths in automobiles and using miles driven as the denominator. However, among alcohol-related deaths, the direction of association was reversed (RR = 0.99, 95 percent CI: 0.97, 1.01) (table 4). Similar weak negative associations were found for alcohol-related deaths in automobiles and using vehicle miles as the denominator.

The incidence of motorcycle fatalities was somewhat greater (RR = 1.08, 95 percent CI: 1.05, 1.11). The direction of association was reversed when we used number of registered motorcycles as the denominator (table 5). Among alcohol-related deaths, the rate ratio was 1.05 (95 percent CI: 1.00, 1.09) (table 5).

Mandatory jail terms for first conviction
When a state mandated a jail term for a first conviction for driving under the influence of alcohol, the incidence of all crash fatalities was slightly greater (RR = 1.02, 95 percent CI: 1.01, 1.03) (table 4). Similar results were obtained for deaths occurring in automobiles and using vehicle miles as the denominator. For all alcohol-related deaths, the association was negative (table 4). A similar association was found for alcohol-related deaths in automobiles and using vehicle miles as the denominator.

The incidence of motorcycle crash fatalities was greater (RR = 1.05, 95 percent CI: 1.01, 1.09) (table 5). The association was reversed when number of registered motorcycles was used as the denominator. For alcohol-related deaths, there was no association between these laws and death (table 5).

Seat-belt laws
Mortality was lower when primary seat-belt laws were in effect, compared with no seat-belt law. For deaths in automobiles only, the rate ratio was 0.90 (95 percent CI: 0.89, 0.92) (table 4). The association with all alcohol-related deaths was 0.94 (95 percent CI: 0.92, 0.97). We found essentially no association with mortality among all vehicle crashes during periods when secondary seat-belt laws were in effect compared with periods without a seat-belt law.

Helmet laws
Mortality was lower when universal helmet laws were in effect, compared with no helmet law (RR = 0.67, 95 percent CI: 0.63, 0.71). We found a weaker association using number of registered motorcycles as the denominator (table 5). The association with alcohol-related deaths was 0.61 (95 percent CI: 0.56, 0.66). Similar results were obtained using number of registered motorcycles as the denominator (table 5).

We found little change in motorcycle mortality during periods in which selective helmet laws were in effect. The association of these laws with mortality in the population younger than 21 years was 1.05 (95 percent CI: 0.91, 1.02).

Interactions between laws
Interactions between laws were examined. No two-way or higher-order interactions were statistically significant (p > 0.05 for all tests).


    DISCUSSION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
From 1980 through 1997, laws mandating a BAC of 0.08 g/dl per se and zero tolerance laws had modest associations with a reduction in overall traffic mortality: approximately 3 percent and 4 percent, respectively. Both had stronger associations with reductions in crash fatalities attributable to alcohol: approximately 14 percent and 12 percent, respectively. Administrative license revocation laws were associated with a 5 percent reduction in overall mortality and alcohol-related mortality. Implementation of mandatory jail terms for persons first convicted for driving under the influence of alcohol was associated with an overall 2 percent increase in traffic mortality, while there was a 5 percent reduction in alcohol-related traffic mortality. Implementation of laws that explicitly allowed police to set up sobriety checkpoints for controlling drinking and driving did not appear to be related to a reduction in overall traffic mortality or alcohol-related traffic mortality.

Our study had several limitations. With the methods used, we were unable to measure any police effort to enforce a law. Substantial variations might occur within a state and between states. We did not account for any policy, law, or program applied at a county or city level. This is especially important for the evaluation of sobriety checkpoints, which have been mostly applied at local levels and at specific times (47). Another potential limitation, one that is common to most studies that deal with this subject, is the high proportion of missing information on BACs. We used multiple imputation methods in an attempt to reduce the bias that may result from only considering data without missing values. We dealt with missing BAC values by employing the multiple imputation methods suggested by Rubin et al. (43); we think the method of Rubin et al. is an improvement over the method of Klein (44), because continuous rather than categorical values of BAC are imputed and because multiple imputation allowed us to account for the uncertainty regarding the missing BAC values. Finally, defining denominators to evaluate the association of laws with deaths is difficult for motorcycle crashes. Data on total vehicle miles driven for motorcycles is not available by state and year, because not all states report this information. Data on registered motorcycles are available but serve only as a rough estimate of motorcycle use.

Our study had several strengths. We used models appropriate for longitudinal count data, took into account changes in mortality over time, and evaluated possible interactions between the laws. We calculated alcohol-related deaths based on the relative risk of being in a fatal crash due to a specific driver BAC, as described by other investigators (38, 48), because this is a more accurate assessment of alcohol-relatedness than proxy measures such as single nighttime crashes (11, 49) or police-reported alcohol consumption (49, 50). This explained the smaller percentage of alcohol-related deaths that we estimated in comparison with some other studies (1, 6, 30, 49, 51, 52).

BAC 0.08 g/dl per se laws
Our finding of a 14 percent reduction in alcohol-related deaths due to implementation of BAC 0.08 g/dl per se laws is similar to that of several recent studies (9, 10, 53). Another study (6) found only five of 11 states to have a significant reduction in mortality. Our findings differ from the findings of a North Carolina study (14) that reported no overall association of these laws with a reduction in alcohol-related deaths.

Two studies (6, 54) used the ratio of the number of fatalities for drinking drivers to the number of fatalities with no drinking drivers as their dependent variable. Another study (9) used a proportion of fatalities rather than the actual count. This use of ratios could bias estimates as described by Kronmal (55) and others (5659). A recent systematic review of studies reported an estimate similar to ours (60).

Zero tolerance laws
Our estimate of a 12 percent reduction in alcohol-related mortality due to the implementation of zero tolerance laws is consistent with findings from other studies as reported in a systematic review (12). Previous studies estimated reductions in mortality between 11 percent and 33 percent after implementation of zero tolerance laws in the United States and Australia. Our finding that the association of these laws was greater among alcohol-related crashes supports the view that these laws affected their target population.

Administrative license revocation laws
Administrative license revocation laws were associated with a 5 percent reduction in overall motorcycle mortality and a 2 percent reduction in alcohol-related motorcycle mortality. This is consistent with findings by Whetten-Goldstein et al. (49), who reported a statistically significant fatality rate difference of –0.04 per 1,000 persons, and Zador et al. (61), who reported a 9 percent reduction in nighttime fatal crashes.

Sobriety checkpoints
Enacting laws that allowed police to set up sobriety checkpoints did not appear to be related to a reduction in overall mortality, and it had a minimal, statistically nonsignificant association with lower alcohol-related mortality. Other studies (47, 6264) have reported a benefit from sobriety checkpoints. Those studies used information about the degree of enforcement, whereas we could not account for actual enforcement.

Mandatory jail terms upon first conviction
For all alcohol-related deaths, mandatory jail terms imposed upon the first conviction for driving under the influence of alcohol were associated with a 5 percent reduction in mortality. Previous studies have differed in their conclusions regarding these measures (49, 6567), ranging from no effect (49, 67) to a 40 percent decrease in reoffending (65).

Other laws
Primary seat-belt laws were associated with reductions in traffic mortality in all crashes and in alcohol-related crashes. This association was slightly weaker for alcohol-related crashes—a finding consistent with evidence that intoxicated drivers are less likely to comply with seat-belt laws (6870). Secondary seat-belt laws appeared to have no association with reductions in traffic mortality among any of the groups studied. This is consistent with other evidence that primary seat-belt laws are more strongly related to mortality reductions than are secondary seat-belt laws (68, 71).

Universal helmet laws appeared to be strongly related to reductions in traffic mortality in all motorcycle crashes, as well as in alcohol-related crashes. Several studies have evaluated the relation of universal helmet laws with mortality (15, 16, 18, 7274), estimating changes that range from 12 percent to 73 percent. Our results are generally consistent with those findings. Selective helmet laws were not associated with significant reductions in motorcycle fatalities.

This study provided information on the effect of alcohol-related laws in the 50 states and the District of Columbia during a period of 18 years. Our results support recent policy measures that set a national level of 0.08 mg/dl for BAC (75). Additional measures such as zero tolerance laws and administrative license revocation laws may also have reduced mortality due to drunk driving.


    ACKNOWLEDGMENTS
 
This study was supported in part by an education grant from the Instituto Colombiano para el Desarrollo de la Ciencia y Tecnología Francisco José de Caldas, "Colciencias" (Bogotá, Colombia) and by a grant from the US Centers for Disease Control and Prevention.


    NOTES
 
Correspondence to Dr. Andrés Villaveces, Instituto Cisalva, Universidad del Valle, Facultad de Salud, Of. 114, Calle 4B #36-00, Dirección Postal 25360, Cali, Columbia (e-mail: avillav{at}laciudad.com). Back


    REFERENCES
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. National Highway Traffic Safety Administration, US Department of Transportation. Traffic safety facts 1998: alcohol. Washington, DC: National Highway Traffic Safety Administration, 1998.
  2. National Highway Traffic Safety Administration, US Department of Transportation. Without motorcycle helmets we all pay the price. Washington, DC: National Highway Traffic Safety Administration, 2000.
  3. Peek-Asa C, Kraus JF. Alcohol use, driver, and crash characteristics among injured motorcycle drivers. J Trauma 1996;41:989–93.[ISI][Medline]
  4. Romano PS, McLoughlin E. Helmet use and fatal motorcycle injuries in California, 1987–1988. J Head Trauma Rehabil 1991;6:21–37.
  5. National Highway Traffic Safety Administration, US Department of Transportation. A report to Congress on the effect of motorcycle helmet use law repeal—a case for helmet use. Washington, DC: National Highway Traffic Safety Administration, 1980.
  6. Apsler R, Char AR, Harding WM, et al. The effects of 0.08 BAC laws. Washington, DC: National Highway Traffic Safety Administration, 1999:1–27.
  7. Deshapriya EB, Iwase N. Are lower legal blood alcohol limits and a combination of sanctions desirable in reducing drunken driver-involved traffic fatalities and traffic accidents? Accid Anal Prev 1996;28:721–31.[CrossRef][ISI][Medline]
  8. Hingson RW, Heeren T, Kovenock D, et al. Effects of Maine’s 1981 and Massachusetts’ 1982 driving-under-the-influence legislation. Am J Public Health 1987;77:593–7.[Abstract]
  9. Hingson R, Heeren T, Winter M. Lowering state legal blood alcohol limits to 0.08%: the effect on fatal motor vehicle crashes. Am J Public Health 1996;86:1297–9.[Abstract]
  10. Hingson R, Heeren T, Winter M. Effects of recent 0.08% legal blood alcohol limits on fatal crash involvement. Inj Prev 2000;6:109–14.[Abstract/Free Full Text]
  11. Rogers PN, Schoenig SE. A time series evaluation of California’s 1982 driving-under-the-influence legislative reforms. Accid Anal Prev 1994;26:63–78.[CrossRef][ISI][Medline]
  12. Zwerling C, Jones MP. Evaluation of the effectiveness of low blood alcohol concentration laws for younger drivers. Am J Prev Med 1999;16:76–80.[CrossRef][ISI][Medline]
  13. McArthur DL, Kraus JF. The specific deterrence of administrative per se laws in reducing drunk driving recidivism. Am J Prev Med 1999;16:68–75.[CrossRef][ISI][Medline]
  14. Foss RD, Stewart JR, Reinfurt DW. Evaluation of the effects of North Carolina’s 0.08% BAC law. Chapel Hill, NC: Highway Safety Research Center, University of North Carolina, 1998:37.
  15. Fleming NS, Becker ER. The impact of the Texas 1989 motorcycle helmet law on total and head-related fatalities, severe injuries, and overall injuries. Med Care 1992;30:832–45.[ISI][Medline]
  16. Muelleman RL, Mlinek EJ, Collicott PE. Motorcycle crash injuries and costs: effect of a re-enacted comprehensive helmet use law. Ann Emerg Med 1992;21:266–72.[ISI][Medline]
  17. McHugh TP, Raymond JI. Safety helmet repeal and motorcycle fatalities in South Carolina. J S C Med Assoc 1985;81:588–90.[Medline]
  18. Mounce N, Brackett Q, Hinshaw W, et al. The reinstated comprehensive motorcycle helmet law in Texas. Alexandria, VA: Insurance Institute for Highway Safety, 1992.
  19. Nelson D, Sklar D, Skipper B, et al. Motorcycle fatalities in New Mexico: the association of helmet nonuse with alcohol intoxication. Ann Emerg Med 1992;21:279–83.[ISI][Medline]
  20. Lund AK. Motorcycle use in Texas. Public Health Rep 1991;106:576–8.[ISI][Medline]
  21. Rollberg CA. The mandatory motorcycle helmet law issue in Arkansas: the cost of repeal. J Ark Med Soc 1990;86:312–16.[Medline]
  22. Sun SW, Kahn DM, Swan KG. Lowering the legal blood alcohol level for motorcyclists. Accid Anal Prev 1998;30:133–6.[CrossRef][ISI][Medline]
  23. Colburn N, Meyer RD, Wrigley M, et al. Should motorcycles be operated within the legal alcohol limits for automobiles? J Trauma 1993;35:183–6.[ISI][Medline]
  24. National Highway Traffic Safety Administration, US Department of Transportation. Fatality Analysis Reporting System. Washington, DC: National Highway Traffic Safety Administration, 1998. (Accessed from http://www.nhtsa.dot.gov/people/ncsa/fars.html on December 1, 1998).
  25. Bureau of the Census, US Department of Commerce. Population statistics. Washington, DC: Bureau of the Census, 1998. (Accessed from http://www.census.gov on December 14, 1998).
  26. Federal Highway Administration, US Department of Transportation. Highway statistics series. Washington, DC: Federal Highway Administration, 1999.
  27. National Highway Traffic Safety Administration, US Department of Transportation. State highway safety laws: key provisions of safety belt use. Washington, DC: National Highway Traffic Safety Administration, 1999:1–2.
  28. National Highway Traffic Safety Administration, US Department of Transportation. State and federal appellate court decisions concerning roadside sobriety checkpoints. Washington, DC: National Highway Traffic Safety Administration, 1998:1–12.
  29. National Highway Traffic Safety Administration, US Department of Transportation. State highway safety laws: motorcycle helmet use. Washington, DC: National Highway Traffic Safety Administration, 1999:1.
  30. National Highway Traffic Safety Administration, US Department of Transportation. State highway safety laws: .08 BAC per se. Washington, DC: National Highway Traffic Safety Administration, 1999:1.
  31. National Highway Traffic Safety Administration, US Department of Transportation. State highway safety laws: administrative license revocation. Washington, DC: National Highway Traffic Safety Administration, 1999.
  32. National Highway Traffic Safety Administration, US Department of Transportation. State highway safety laws: lower BACs for youthful DWI offenders. Washington, DC: National Highway Traffic Safety Administration, 1999:1.
  33. National Highway Traffic Safety Administration, US Department of Transportation. A digest of state alcohol-highway safety related legislation. Washington, DC: National Highway Traffic Safety Administration, 1983–1997.
  34. Hardin J, Hilbe J. Generalized linear models and extensions. College Station, TX: Stata Press, 2001.
  35. Stata Corporation. Stata reference manual. College Station, TX: Stata Press, 1997.
  36. Rothman KJ, Greenland S. Modern epidemiology. Philadelphia, PA: Lippincott-Raven, 1998.
  37. Zador PL, Krawchuk SA, Voas RB. Alcohol-related relative risk of driver fatalities and driver involvement in fatal crashes in relation to driver age and gender: an update using 1996 data. J Stud Alcohol 2000;61:387–95.[ISI][Medline]
  38. Hurst PM, Harte D, Frith WJ. The Grand Rapids dip revisited. Accid Anal Prev 1994;26:647–54.[CrossRef][ISI][Medline]
  39. Rubin DB. Multiple imputation for nonresponse in surveys. New York, NY: John Wiley and Sons, Inc, 1987.
  40. Rubin DB, Schenker N. Multiple imputation in health-care databases: an overview and some applications. Stat Med 1991;10:585–98.[ISI][Medline]
  41. Schafer JL. Analysis of incomplete multivariate data. New York, NY: Chapman and Hall, Inc, 1997.
  42. Heitjan DF. Multiple imputation for the Fatal Accident Reporting System. Appl Stat 1991;40:13–29.[ISI]
  43. Rubin DB, Schafer JL, Subramanian R. Multiple imputation of missing blood alcohol concentration (BAC) values in FARS. Washington, DC: National Highway Traffic Safety Administration, 1998.
  44. Klein TM. A method for estimating posterior BAC distributions for persons involved in fatal traffic accidents. Washington, DC: National Highway Traffic Safety Administration, 1986.
  45. Schafer JL. Software for multiple imputation. University Park, PA: Department of Statistics, Pennsylvania State University, 1997.
  46. MathSoft, Inc. S-Plus 4.5 professional. Seattle, WA: MathSoft, Inc, 1997.
  47. Lacey JH, Jones RK, Smith RG. Evaluation of Checkpoint Tennessee: Tennessee’s statewide sobriety checkpoint program. Washington, DC: National Highway Traffic Safety Administration, 1999:24.
  48. Zador PL, Lund AK, Field M, et al. Alcohol-impaired driving laws and fatal crash involvement. Alexandria, VA: Insurance Institute for Highway Safety, 1988.
  49. Whetten-Goldstein K, Sloan FA, Stout E, et al. Civil liability, criminal law, and other policies and alcohol-related motor vehicle fatalities in the United States: 1984–1995. Accid Anal Prev 2000;32:723–33.[CrossRef][ISI][Medline]
  50. DeJong W, Hingson R. Strategies to reduce driving under the influence of alcohol. Annu Rev Public Health 1998;19:359–78.[CrossRef][ISI][Medline]
  51. Decker MD, Graitcer PL, Schaffner W. Reduction in motor vehicle fatalities associated with an increase in the minimum drinking age. JAMA 1988;260:3604–10.[Abstract]
  52. Kennedy BP, Isaac NE, Nelson TF, et al. Young male drinkers and impaired driving intervention: results of a U.S. telephone survey. Accid Anal Prev 1997;29:707–13.[CrossRef][ISI][Medline]
  53. Dee TS. Does setting limits save lives? The case of 0.08 BAC laws. J Pol Anal Manag 2001;20:111–28.
  54. Voas RB, Tippetts AS, Fell J. The relationship of alcohol safety laws to drinking drivers in fatal crashes. Accid Anal Prev 2000;32:483–92.[CrossRef][ISI][Medline]
  55. Kronmal RA. Spurious correlation and the fallacy of the ratio standard revisited. J R Stat Soc A 1993;156:379–92.[ISI]
  56. Jackson DA, Somers KM. The spectre of "spurious" correlations. Oecologia 1991;86:147–51.[ISI]
  57. Berges JA. Ratios, regression statistics, and "spurious" correlations. Limnol Oceanogr 1997;42:1006–7.
  58. Firebaugh G, Gibbs JP. User’s guide to ratio variables. Am Soc Rev 1985;50:713–22.[ISI]
  59. Logan CH. Problems in ratio correlation: the case of deterrence research. Soc Forces 1982;60:791–810.[ISI]
  60. Shults RA, Elder RW, Sleet DA, et al. Reviews of evidence regarding interventions to reduce alcohol-impaired driving. Am J Prev Med 2001;21:66–88.[ISI][Medline]
  61. Zador PL, Lund AK, Fields M, et al. Fatal crash involvement and laws against alcohol-impaired driving. J Public Health Pol 1989;10:467–85.[Medline]
  62. Peek-Asa C. The effect of random alcohol screening in reducing motor vehicle crash injuries. Am J Prev Med 1999;16:57–67.[CrossRef][ISI][Medline]
  63. Levy D, Shea D, Asch P. Traffic safety effects of sobriety checkpoints and other local DWI programs in New Jersey. Am J Public Health 1989;79:291–3.[Abstract]
  64. Homel R. Drink-driving law enforcement and the legal blood alcohol limit in New South Wales. Accid Anal Prev 1994;26:147–55.[CrossRef][ISI][Medline]
  65. Socie EM, Wagner SA, Hopkins RS. The relative effectiveness of sanctions applied to first-time drunken driving offenders. Am J Prev Med 1994;10:85–90.[ISI][Medline]
  66. Ross HL, Klette H. Abandonment of mandatory jail for impaired drivers in Norway and Sweden. Accid Anal Prev 1995;27:151–7.[CrossRef][ISI][Medline]
  67. Martin SE, Annan S, Forst B. The special deterrent effects of a jail sanction on first-time drunk drivers: a quasi-experimental study. Accid Anal Prev 1993;25:561–8.[CrossRef][ISI][Medline]
  68. Dee TS. Reconsidering the effects of seat belt laws and their enforcement status. Accid Anal Prev 1998;30:1–10.[CrossRef][ISI][Medline]
  69. Foss RD, Beirness DJ, Sprattler K. Seat belt use among drinking drivers in Minnesota. Am J Public Health 1994;84:1732–7.[Abstract]
  70. Lange JE, Voas RB. Nighttime observations of safety belt use: an evaluation of California’s primary law. Am J Public Health 1998;88:1718–20.[Abstract]
  71. Rivara FP, Thompson DC, Cummings P. Effectiveness of primary and secondary enforced seat belt laws. Am J Prev Med 1999;16:1–11.
  72. Sosin DM, Sacks JJ. Motorcycle helmet-use laws and head injury prevention. JAMA 1992;267:1649–51.[Abstract]
  73. Chiu WT, Kuo CY, Hung CC, et al. The effect of the Taiwan motorcycle helmet use law on head injuries. Am J Public Health 2000;90:793–6.[Abstract/Free Full Text]
  74. Ferrando J, Plasencia A, Oros M, et al. Impact of a helmet law on two wheel motor vehicle crash mortality in a southern European urban area. Inj Prev 2000;6:184–8.[Abstract/Free Full Text]
  75. Associated Press. Clinton signs drunken driving bill. New York, NY: New York Times, October 24, 2000:3.