Reducing Death on the Road:The Effects of Minimum SafetyStandards, Publicized Crash Tests,Seat Belts, and Alcohol

Leon S. Robertson, PhD

IntroductionVehicle-related deaths on US roads

have declined from more than 50 000 peryear to about 40 000 per year in the past25 years, during which the numbers ofregistered vehicles doubled, miles drivensimilarly increased, and cars becamesmaller. The rate of deaths per hundredmillion vehicle miles, which was 5.5 in1966, when the Motor Vehicle Safety Actwas enacted, was 1.8 in 1992.1

The effects on these rates of govern-ment safety standards, which have setperformance criteria for crashworthinessand crash avoidance that must be met orexceeded, and laws requiring seat belt useare disputed. Neoclassic economists ar-gue that drivers protected by more crash-worthy cars or seat belts drive moreriskily, offsetting the effects of the regula-tions as a result of increased collisionswith other road users. Claimed supportfor this theory is mainly based on regres-sion analysis of ripples in various timeseries2'3 or self-reported claims of seat beltuse.4 Disaggregation of data, separatingregulated from unregulated vehicles, indi-cated incremental reductions in occupantfatalities in regulated vehicles during thelate 1960s and 1970s and no adverse effecton other road users.'10 Self-reports ofseat belt use are known to be invalid.11"12

Actual observations of seat belt useand driving behaviors before and after abelt use law, in comparison with observa-tions in a jurisdiction with no law, re-vealed no changes in risky behaviors (e.g.,speeding, running stop signs and redlights, following too closely) that sug-gested riskier behavior when drivers in-crease seat belt use.13

The history of federal and stateefforts to reduce motor vehicle injuriesprovides an opportunity to estimate theeffects of "minimum" safety standards,

improved crashworthiness (at least partlymotivated by embarrassment to manufac-turers and competitive concerns causedby publicity regarding crash tests), seatbelt use (increased mainly by laws requir-ing use), reductions of alcohol use indrivers, and potential offsetting behavior.

Adoption of safety standards virtu-ally ceased from 1978 to 1987. The federalstandard that required seat belts automati-cally encircling front-outboard occupantsor, altematively, air bags was rescinded bythe Reagan administration and was re-stored in the late 1980s only after thecourts ruled that the administration hadacted illegally. The National HighwayTraffic Safety Administration did con-tinue frontal crash tests of a selection ofcars annually and published the results.Manufacturers were embarrassed enoughby the reported forces on occupant testdummies at 35 miles per hour that, onoccasion, they requested a retest aftermodifying the vehicles.

The crash tests indicated incremen-tal improvement in crashworthiness dur-ing the 1980s, as evidenced by reducedforces on crash test dummies. Researchon fatalities to occupants in frontal crashesindicated a reduced number of deaths infrontal crashes of vehicles that performedwell in crash tests,14'15 but the researchdesigns of these studies did not allow forthe possibility of offsetting behavior. Seatbelt use laws, enacted by the states from1985 to 1990, largely accounted for morethan doubling of seat belt use,16 and

The author is with the Department of Epidemi-ology and Public Health, Yale University, NewHaven, Conn, and Nanlee Research, Branford,Conn.

Requests for reprints should be sent toLeon S. Robertson, PhD, Nanlee Research, 2Montgomery Pkwy, Branford, CT 06405-5115.

This paper was accepted August 8, 1995.

American Journal of Public Health 31

Robertson

TABLE 1-Passenger Car FatalityRates per 100 MillionVehicle Miles: 1975through 1977 Models,by Vehicle Age

Rate per100 Million Miles

NonoccupantVehicle Occupant DeathsAge, y Deaths from Crashes

1 2.182 2.273 2.414 2.645 2.716 2.577 2.698 2.579 2.6510 2.8311 3.0112 3.4013 2.9214 2.9515 2.79

1.751.881.982.212.102.012.011.972.292.342.702.702.452.371.74

alcohol in fatally injured drivers declinedabout 10 percentage points during the1980s17 as a result of a variety of factors.The purpose of this paper is to assess thecontribution of each of these changes tothe reduction in passenger car fatalityrates, as well as any evidence of offsettingbehavior.

Data andMethodsDeath rates per 100 million miles in

terms of passenger cars, by model year ofthe vehicle and whether the death was toone or more occupants of the car, were

obtained by means of several methodsand data sources for model years 1961through 1990 in each of the calendar years1975 through 1991.* Miles per vehicle of a

*As an example of data elements in theanalysis, the following are elements for 1986model cars in calendar year 1989: miles drivenby 3-year-old cars in 1988 = 10 55018; ratio ofaverage miles in 1989 to average miles in1988 = 1.0319; 1986 model cars registered in1989 = 10 489 00020; estimated 100 millionmiles use = 10 550 x 1.03 x 0.10489 = 1,139.8;occupant fatalities = 201221 (rate = 2012/1139.8 = 1.77);nonoccupant fatal crash involve-ment2l = 1025 (rate = 0.90); years since regula-tion began = 1986 - 1966 > 12, therefore 12;years since NCAP publicity began = 1986 -

1979 = 7; % observed belt use in 1986 modelsduring 198927 = 56; % dead drivers of 1986models in 1989 with blood alcohol > 0.10% =

31 (based on states where 80 percent or moreare assayed for alcohol)28; Index of IndustrialProduction, 1989 = 106.8.26

given age in the 1988 mileage survey were

adjusted to those of other years bymultiplying them by the ratio of average

miles driven in other years to the 1988average. The mileage survey includedperiodic calls to the same households toobtain odometer readings,18 which isprobably more valid than asking peopletheir annual mileage. Rates were avail-able on 254 combinations of vehiclemodel year and calendar year.

Two sets of rates per 100 millionmiles were analyzed separately: occupantfatalities and crashes fatal to nonoccu-

pants (occupants of other vehicles inmultiple-vehicle crashes, pedestrians, andbicyclists). The first allowed an estimateof the effects of safety standards, im-proved crashworthiness, and the otherfactors on all occupant deaths. Thesecond allowed examination of the pos-

sible effects on other road users. If there isoffsetting behavior, nonoccupant deathrates should increase in relation to regula-tion, crash test publicity, and belt use.

Since some safety standards were

imposed by the General Services Adminis-tration in 1966 on cars sold to thegovernment and the standards for all cars

began to be imposed in 1968, the absenceof standards was correlated with vehicleage. Data on the 1975 through 1977models were available for a full 15 years ofvehicle use. The death rates (each of thetwo sets separately) per mile were calcu-lated for these model years for each yearof age and averaged among the threemodel years. These rates are presented inTable 1. Note that the death rates are

neither linear nor monotonic as thevehicles age. A graph of the preregulationmodels by age (available from the author)

indicates that the pattern of older, pre-

regulation vehicles is similar to that ofvehicles 10 years old and older in Table 1.Use of the 1975 through 1977 rate for a

vehicle of a given age as the expected ratefor a vehicle of that age controlled forvariation attributable to vehicle age.

Other factors considered were thedownsizing of vehicles and the economicconditions during a given calendar year,

both of which have been correlated withdeath rates,22 observed seat belt use in a

given calendar year, and percentage ofdrivers with alcohol greater than 0.10%by weight in a given calendar year.

Smaller vehicles have higher occupantdeath rates because of less interior space

to decelerate, and, for unknown reasons,

deaths per mile are marginally higher inyears of greater economic prosperity.Wheelbase, the distance from the front torear axle, has been shown to be the bestpredictor of differences in fatality ratesdue to vehicle size.23 As a means ofcontrolling for vehicle size, the death ratesper mile in calendar year 1988 were

calculated for seven categories in 5-inincrements of wheelbase (from < 95.1 to120.1+); the 1988 mileage survey anddecoded vehicle identification numbersfor make and model of vehicle in the fatalfile and mileage survey file were used inthese calculations. Expected fatalitieswerecalculated by multiplying the 1988 rate foreach size by the number ofvehicles of thatsize sold in a given model year (dis-counted for scrappage as they aged).2425The expected number was then divided bythe mileage previously estimated for eachmodel and calendar year. The index of

32 American Journal of Public Health

TABLE 2-Regression Estimation of Passenger Car Fatality Rates per 100Million Vehicle Miles: 1961 through 1990 Cars in 1975 through 1991

Nonoccupant DeathsOccupant Deaths from Crashes

Effect 95% Cl Effect 95% Cl

Standards -0.260 -0.237, -0.283 -0.055 -0.045, -0.065NCAP publicity -0.077 -0.044, -0.110 -0.029 -0.009, -0.049Seat belt use, % -0.007 -0.001, -0.013 -0.006 -0.002, -0.010Alcohol > 0.10, % 0.007 0.001, 0.013 0.007 0.002, 0.012Calendar year -0.017 -0.052, 0.019 -0.016 -0.038, 0.006Industrial production 0.029 0.015, 0.043 0.019 0.010, 0.028Expected from age of vehicle 0.444 0.656, 0.232 0.289 0.193, 0.385Expected from wheelbase 1.066 0.612,1.520 1.252 1.047,1.551

Intercept -0.793 -1.950R2 .92 .86

Note. Cl = confidence interval; NCAP = New Car Assessment Program.

January 1996, Vol. 86, No. 1

Auto Fatality Rates

industrial production was used as anindicator of economic activity. Seat beltuse in a given model-calendar year wasincluded from an annual survey of 19cities and their environs, extrapolating fora few years in which the survey was notdone.27 Alcohol in fatally injured driversfor each model-calendar year was ob-tained in states that test 80% or more ofsuch drivers.28

Ordinary least squares regressionwas used to estimate the effects of thevarious factors. The variable for minimumsafety standards was zero for pre-1966models, incremented from I to 12 in 1966through 1977 models, and 12 for 1978through 1991 models. As noted, thereduction in occupant death rates hasbeen shown to be incremental in 1966through 1977 models, partly because ofthe imposition of new standards in variousyears of that period and partly because ofdelays in meeting the standards in somemodels.5-929 The publication of New CarAssessment Program (NCAP) crash testresults began in 1979, so the NCAPvariable was zero for 1961 through 1979models and incremented by one (from 1to 11 consecutively) for 1980 through 1990models, based on the assumption thatcrashworthiness was improved incremen-tally as the crash test results for particularmakes and models became known.

ResultsThe regression coefficients for the

predictor variables are presented in Table2. After the expected effects of vehicle ageand size differences had been controlled,the incremental model years in whichminimum safety standards were imposedand the model years during which NCAPtests were publicized were strong predic-tors of reduced occupant death rates andreduced occupant and total fatal crashrates. The improvements were largerduring the period of minimum safetystandards than during that of publicizedcrash tests. Increased seat belt use wasalso correlated with a reduction in occu-pant fatalities per mile. Higher crash rateswere found in the model-calendar yearsin which more alcohol was found indrivers, as expected. Contrary to offsettingbehavior theory, the coefficients for regu-lation, NCAP tests, and seat belt use werenegative in relation to nonoccupant in-volvement rates.

In each case, rates were marginallyhigher in more economically prosperousyears, as indicated by the predictivecoefficient on the index of industrial

production. When all of the other factorswere controlled, the trend by calendaryear was not significant. The R2 value ineach case indicated excellent fit of thedata to the regression models.

DiscussionThe results support the conclusion

that car occupant deaths have beenreduced substantially by safety standardsand publicized crash tests leading toincreased crashworthiness. The reduc-tions were specific to model years in whichthese activities were occurring rather thanto a trend by calendar year. Examinationof plots of residuals from regression of theother predictor variables indicated thatthe effects were linear and not influencedby outliers. Increased seat belt use andreduced alcohol use had additional ef-fects.

The fact that the reduction in deathswas largely a linear function of vehiclemodel year during the period of regula-tion and NCAP tests suggests that, inaddition to meeting the standards orimprovement in performance on the tests,manufacturers were devoting attention tocrashworthiness generally. For example,although there is no standard for so-called"crumple zones" to better absorb energyin crashes, manufacturers have increas-ingly designed them into vehicles.

The fact that reductions in nonoccu-pant fatalities were associated with regula-tion, NCAP testing, and seat belt use isnot anomalous. Some regulations wereaimed at crash avoidance (reduced glarein drivers' eyes, side running lights). Sharppoints on front ends were reduced in the1980s when NCAP testing was beingdone. A general increase in seat belt useincreased protection in the "other" ve-hicles in collisions.

The econometric analyses claimingoffsetting behavior are misleading.30 Ironi-cally, the most recent claim of offsettingbehavior by economists3 is probably aresult of the federal government's failureto regulate trucks and utility vehicles.Lack of distinction of passenger cars frompickup trucks and utility vehicles in atime-series analysis will give false resultsin terms of the effects of regulation onpassenger cars. The reason is not that theregulated cars are more often hittingtrucks and other road users, as claimed byproponents of time-series analyses, butthat the government has failed to imposestandards to reduce rollover of unstablepickup trucks and utility vehicles, whichhave grown substantially in use. The

rollover rates of the less stable of thesevehicles are 3 to 20 times those ofpassenger cars.31-35 O

References1. National Highway Traffic Safety Adminis-

tration. Traffic Safety Facts, 1992. Washing-ton, DC: US Dept of Transportation; 1994.

2. Peltzman S. The effects of automobilesafety regulation. J Pol Econ. 1975;83:677-725.

3. Chirinko RS, Harper EP. Buckle up orslow down? New estimates of offsettingbehavior and their implications for automo-bile safety regulation. J Pol Anal Man.1993;12:270-296.

4. Garbacz C. Estimating seat belt effective-ness with seat belt usage data from theCenters for Disease Control. Econ Let.1990;34:83-88.

5. Robertson LS. A critical analysis of Peltz-man's 'The effects of automobile safetyregulation.'JEcon Issues. 1977;11:587.

6. Graham JD, Garber S. Evaluating theeffects of automobile safety regulation. JPolAnal Man. 1984;3:206-224.

7. Robertson LS. State and federal new-carsafety regulation: effects on fatality rates.AccAnalPrev. 1977;9:151-156.

8. Robertson LS. Automobile safety regula-tions and death reductions in the UnitedStates. Am J Public Health. 1981;71:818-822.

9. Graham JD Technology, behavior, andsafety: an empirical study of automobileoccupant-protection regulation. Policy Sci.1984;74:141-151.

10. Robertson LS. Automobile safety regula-tion: rebuttal and new data. Am J PublicHealth. 1984;74:1390-1394.

11. Waller PF, Barry PZ. SeatBelts:A Compari-son of Observed and Reported Use. ChapelHill, NC: University of North CarolinaHighway Safety Research Center; 1969.

12. Robertson LS. The validity of self-reportedbehavioral risk factors: seatbelt and alcoholuse. J Trauma. 1992;32:58-59.

13. Lund AK, Zador PL. Mandatory belt useand driver risk taking. Risk AnaL 1984;4:41-53.

14. Kahane CJ. Correlation of NCAP Perfor-mance with Fatality Risk in Actual Head-OnCollisions. Washington, DC: National High-way Traffic Safety Administration; 1994.

15. Zador PL, Jones IS, Ginsburg M. Fatalfront-to-front car collisions and the resultsof 35 MPH frontal barrier impacts. In: 28thAnnual Proceedings of the Am. Assn. Auto.Med., Denver, Colo: 1984.

16. Datta TK, Guzek P. Restraint System Use in19 U.S. Cities: 1989AnnualReport. Washing-ton, DC: US Dept of Transportation; 1990.

17. Klein TM, Burgess M.Alcohol Involvementin Fatal Crashes-1992. Washington, DC:National Highway Traffic Safety Adminis-tration; 1994.

18. Energy Information Administration. House-hold Vehicles Energy Consumption, 1988.Washington, DC: US Dept of Energy;1990.

19. Federal Highway Administration. HighwayStatistics. Washington, DC: US Dept ofTransportation; 1975-1992.

20. Ward'sAutomotive Yearbook Detroit, Mich:Ward's Communications; 1960-1992.

January 1996, Vol. 86, No. 1 American Journal of Public Health 33

Robertson

21. National Highway Traffic Safety Adminis-tration. FARS 91. Washington, DC: USDept of Transportation; 1993.

22. Robertson LS. Injury Epidemiology. NewYork, NY: Oxford University Press Inc;1992.

23. Robertson LS. How to save fuel andreduce injuries in automobiles. J Trauma.1991;31:107-109.

24. Flammang JM. Standard Catalog of Im-ported Cars, 1946-1990. Iola, Wis: KrausPublications; 1992.

25. Automotive News Almanac Issue. Detroit,Mich: Automotive News Inc; 1960-1992.

26. Economic Indicators. Washington, DC:Council of Economic Advisors; 1994.

27. National Highway Traffic Safety Adminis-tration. Restraint System Use in the Traffic

Population. Washington, DC: US Dept ofTransportation; 1975-1991.

28. National Highway Traffic Safety Adminis-tration. Fatal Accident Reporting System1988. Washington, DC: US Dept of Trans-portation; 1989.

29. National Highway Traffic Safety Adminis-tration. Standards Enforcement Tests Re-ports Index Washington, DC: US Dept ofTransportation; 1969-1980.

30. Leamer EE. Let's take the con out ofeconometrics.Am Econ Rev. 1983;73:31-43.

31. Snyder RG, McDole TL, Ladd WM,Minahan DJ. On-Road Crash Experience ofUtility Vehicles. Ann Arbor, Mich: Univer-sity of Michigan Highway Safety ResearchCenter, 1980.

32. Reinfurt DW, Li LK, Popkin CL, O'Neill

B, Burchman PF, Wells JAK. A Compari-son of Crash Expenence of Utility Vehicles,Pickup Trucks and Passenger Cars. ChapelHill, NC: University of North CarolinaHighway Safety Research Center; 1981.

33. Robertson LS. Risk of fatal rollover inutility vehicles relative to static stability.Am JPublic Health. 1989;79:300-303.

34. Jones IS, Penny MB. Engineering Param-eters Related to Rollover Frequency. Warren-dale, Pa: Society of Automotive Engineers;1990.

35. Harwin EA, Brewer HK. Analysis of therelationship between vehicle rollover stabil-ity and rollover risk using the NHTSACARDfile Accident Database. J TrafMed.1990;18:109-122.

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