United States General Accounting Office

GAO Report to Congressional Requesters

May 1995 HIGHWAY SAFETY

Reliability and Validity

of DOT Crash Tests

GAO/PEMD-95-5

GAO United States

General Accounting Office

Washington, D.C. 20548

Program Evaluation and

Methodology Division

B-250144 

May 5, 1995

The Honorable Ernest F. Hollings

Ranking Minority Member

Committee on Commerce, Science,

 and Transportation

United States Senate

The Honorable Richard H. Bryan

United States Senate

Between 1980 and 1992, the annual death toll on America’s highways

dropped from more than 50,000 to less than 40,000. One factor

contributing to this decline may have been the increasing concern among

consumers about the safety of the vehicles they purchase. The crash test

programs performed by the Department of Transportation (DOT) are the

major source of the safety information available to today’s automobile

purchaser.

You asked us to supplement our earlier testimony and report to your

Committee on the relationship between automotive design factors and

safety by responding to a number of questions concerning automobile

safety. As one component of this research, you requested that we review

the automobile crashworthiness program of the National Highway Traffic

Safety Administration (NHTSA) to determine whether NHTSA’s crash test

programs provide valid and reliable indicators of occupant safety in

real-world crashes.

Background The Department of Transportation has four offices that conduct

automobile crash tests: three within NHTSA and one in the Federal Highway

Administration (FHWA). The activities of two programs run by NHTSA are the

focus of this report. NHTSA’s Office of Vehicle Safety Compliance performs

a compliance testing program of 30-mile-per-hour full-frontal crashes of

automobiles, light trucks, and vans into a fixed rigid barrier. This program

was created under section 103 of the National Traffic and Motor Vehicle

Safety Act of 1966, and it is designed to ensure that vehicles meet

minimum safety requirements as specified in Federal Motor Vehicle Safety

Standard No. 208 -Occupant Crash Protection (FMVSS 208).1

1

Code of Federal Regulations, 49 C.F.R. Part 571: Federal Motor Vehicle Safety Standards (FMVSS),

Standard No. 208 - Occupant Crash Protection. The Office of Vehicle Safety Compliance also uses

dynamic crash tests to determine vehicular compliance with FMVSS 212, Windshield Mounting; FMVSS

219, Windshield Zone Intrusion; and FMVSS 301, Fuel System Integrity.

Page 1 GAO/PEMD-95-5 Department of Transportation Crash Tests
B-250144 

Also under the authority of NHTSA is the New Car Assessment Program

(NCAP), conducted by the Office of Market Incentives. This program,

mandated under title II of the Motor Vehicle Information and Cost Savings

Act of 1972, was created to provide information to consumers on the

relative crashworthiness, or safety, of automobiles. This charge differs

from the compliance test in that vehicles tested in NCAP are not required to

meet specified safety standards, while the purpose of compliance tests is

to ensure that vehicles meet a level of safety required by law. The NCAP test

also differs from the compliance test in two important aspects: NCAP

crashes its vehicles at 35 miles per hour, which translates to over one-third

more energy than compliance tests, and NCAP engages all manual and

automatic restraints, while the compliance test employs only passive

restraints. By using all restraint systems, NCAP assesses the maximum

crashworthiness of a vehicle in high-speed frontal crashes.

In addition to the two programs described above, NHTSA’s Office of

Crashworthiness Research conducts a variety of tests to study a wide

range of individual safety issues that arise from specific crash

configurations. FHWA conducts crash tests to study the interaction between

automobiles and roadside obstacles and devices such as guard rails,

telephone poles, and bridge abutments.

Objectives, Scope,

and Methodology

To respond to your request, we examined data from tests conducted for

compliance with FMVSS 208 (compliance tests) as well as those conducted

under the New Car Assessment Program. We chose to focus on these

programs because both conduct tests that are similarly configured, employ

standardized procedures, and have been assessing vehicle

crashworthiness over a period of years. The two other crash test programs

run by DOT are largely research based and, although important, have

different purposes from those of our study.

Our analysis consisted of three parts: (1) an examination of trends over

time in crash test results of both programs, (2) an assessment of the

reliability of NCAP results, and (3) a review of the relationship between

NCAP results and real-world traffic injuries and fatalities. We first reviewed

the background, sample selection, and testing procedures of both NCAP and

the compliance program. (See appendix I). We then examined what it is

that crash tests measure, as wellas how well measurement devices used in

crash tests simulate human biomechanics and physiological response by

reviewing biomechanic, human tolerance, and automotive safety literature

and by interviewing experts in those fields. (See appendixes II and III.)

Page 2 GAO/PEMD-95-5 Department of Transportation Crash Tests
B-250144 

Next, we analyzed changes in crash test results by year for both the

compliance program and NCAP. (See appendix IV.)

To address the reliability of crash test results, that is, the degree to which

consistent results are obtained through repeated trials, we examined

research conducted by NHTSA and compared NCAP results with those

obtained in crash tests conducted by manufacturers. (See appendix V.)

Finally, we conducted analyses using two national databases that allowed

us to relate real-world fatality rates for drivers with the predicted injury

risks derived from NCAP results. (See appendix VI). For this analysis, we

used Poisson regressions to assess the relationship between fatality rates,

derived from the Fatal Accident Reporting System and the R.L. Polk

Vehicle Registration System, and the combined injury risk calculated from

the NCAP measurements that assess the potential for skeletal injuries to the

head and chest. Analyses were conducted for restrained drivers in oneand two-car frontal crashes.

We did not include information from the compliance program in the

analyses we conducted on either the reliability or the predictive validity of

crash test results. In our assessment of the reliability of crash test results,

we did not uncover a quantity of data sufficient enough to compare the

results of two or more trials of vehicle models. In the case of the

predictive validity of crash test results, we did not use compliance test

data for two reasons. First, the compliance program had conducted only

145 tests between 1987 and 1992. Second, the variation among compliance

results was relatively narrow and scores tended to cluster far below the

ceiling values for the compliance tests. These two items resulted in a

dataset that was insufficient for conducting detailed statistical analyses.

We conducted our review in accordance with generally accepted

government auditing standards.

Results in Brief Recent trends in test results indicate that, first, the probability of

sustaining a serious injury, as it is measured by the NCAP and compliance

tests, has decreased substantially since the inception of these test

programs. In addition, the variation in scores between automobile models

has shrunk, indicating that cars marketed in the United States have

become more uniformly crashworthy. Some of this improvement, we

concluded, could appropriately be attributed to DOT crash test programs

initiated by the National Traffic and Motor Vehicle Safety Act of 1966 and

the Motor Vehicle Information and Cost Savings Act of 1972.

Page 3 GAO/PEMD-95-5 Department of Transportation Crash Tests
B-250144 

Second, the reliability, that is, the consistency of results derived from NCAP

tests is questionable. Existing evidence suggests that large differences

between crash test scores most likely reflect true differences between

vehicles. However, we cannot be sure that even moderately large score

differences between two vehicles might not disappear or be reversed if

they were tested again. This is because, in general, only one unit of a

specific vehicle line is tested, and this is not enough to say with

confidence that the results are indicative of how other units of that same

vehicle line would perform. The new star rating system incorporated by

NCAP in recent years, a system that places vehicles into one of five

categories on the basis of potential injury risk, could exacerbate this

problem in some cases.

Third, we found that the ability of NCAP to predict a vehicle’s occupant

protection in real-world crashes is limited. By their nature, NCAP crash test

results can be validly applied only to frontal collisions, which account for

slightly more than half of all injury-producing accidents. We found a

statistically significant relationship between fatality rates and NCAP

predicted injury risk; however, this relationship derives from the high

fatality rates associated with the poorest performers in NCAP (the

20 percent of vehicles with the highest potential injury risks derived from

NCAP results).

GAO’s Analysis

Automobiles Have Become

More Crashworthy

In NCAP crashes, nearly all cars now meet the head and chest injury

standards of the compliance tests, although they are 36-percent more

violent than compliance crashes. The average probability of sustaining a

serious injury in a 35 mile-per-hour crash as measured by NCAP has

declined from over 0.5 in 1980 to less than 0.2 in 1993. (See figure 1.)

Differences among the crashworthiness scores of vehicles tested in this

program have experienced similar declines. The introduction of air bags

has contributed significantly to this improvement. (For a complete

discussion of the trends in crash test results, see appendix IV.)

Page 4 GAO/PEMD-95-5 Department of Transportation Crash Tests
B-250144 

Figure 1: Mean NCAP Injury Risk by Model Yeara

Injury Risk

0

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.900

1.000

1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993

Model Year

aFor all passenger cars. Does not include light trucks and vans.

A causal linkage between improved crash test scores and declining

highway fatalities cannot be asserted with certainty because of both the

many variables involved in a crash and the increased emphasis on traffic

accident and injury prevention over the past decade. Nonetheless, it seems

reasonable to conclude that manufacturers’ successful efforts to improve

their products’ performance in NHTSA crash tests, particularly in NCAP, have

contributed to improved occupant protection in real-world crashes,

although we were unable to quantify that contribution. These

improvements to performance have derived from a variety of efforts, with

two examples being modernized manufacturing techniques and an

increased emphasis on safety systems and designs.

In addition, in recent years, automotive designers have turned more to

computer-based simulations to assist in the design of vehicles that meet

crash test standards. Although we did not evaluate the state of the art in

computer-based crash models, we learned from industry personnel that

such modeling appears to accurately predict the results of actual crash

tests. Indeed, one computer specialist informed us that the industry uses

crash tests in part to validate their computer models.

Page 5 GAO/PEMD-95-5 Department of Transportation Crash Tests
B-250144 

Although simulated crashes are costly as they currently require access to

supercomputers, they do allow the manufacturer to assess the

crashworthiness of a vehicle in more trials, more quickly, and at impacts

points other than the front (or side) of a car. These benefits over actual

crash testing permit the identification of crash forces upon an occupant in

a time frame that offers immediate redesign implications.

Crash Test Results Have

Questionable Reliability

To determine whether the result of any test is reliable, consistent results

must be obtained through repeated trials of a specified procedure. In the

case of crash tests, this means that consistent results of repeated tests of a

specific vehicle model are required. This is particularly crucial when

comparing the safety ratings of different vehicles. Both the NCAP and

compliance programs generally conduct only one trial of a specific vehicle

model; thus, insufficient data exist to accurately define the reliability of

crash test results. That is, the ability to predict with confidence the

likelihood of a tested model’s receiving similar scores if tested again is

low.

We found only two sources of information on which to assess the

reliability of crash test results: a study conducted by NHTSA in 1984, which

examined the variations in test results of 12 consecutively manufactured

Chevrolet Citations, and our own analysis of the differences between

results for vehicle models tested in NCAP and the results for those vehicles

in corresponding tests conducted by automobile manufacturers. Our

analysis of the data derived from NHTSA’s 1984 study revealed wide

variations in the head injury criterion (HIC) results, the measurement taken

to assess potential skeletal head injuries. (See appendix V.) Although

NHTSA ascribed the variation in results to a number of sources, including

the test itself, it failed to discuss the implications of the combined effect of

these sources on crash test results; namely, that even within a specific

vehicle line, the result of one test may not be indicative of the model’s

performance from trial to trial, and large differences in the resultant HIC

may occur.

We also examined the differences between the results of NCAP and

manufacturers’ tests provided to us by NCAP officials. The tests conducted

by the manufacturers essentially duplicated the NCAP test procedures. We

compared the results of the two tests using the star rating system recently

developed by NCAP, hypothesizing that if the manufacturer test were

considered a second trial for a model line, its results should be consistent

with the NCAP, or first trial. The star rating system ranks cars from 1 to 5

Page 6 GAO/PEMD-95-5 Department of Transportation Crash Tests
B-250144 

stars, with 5 stars being the best rating, or safest car, and 1 star being the

worst rating, or least safe car. These ratings are based on the risks of

serious injury for vehicles, which are calculated from the head injury

criterion and chest acceleration scores from NCAP tests. (For a discussion

of crash test measurements and the star system, see appendix II.)

We found that in only about one-half of the paired comparisons would

NCAP- and manufacturer-tested vehicles have received the same star rating.

In 32 percent of the comparisons, the results of the second trial would

have changed by 1 star, while in 8 percent of the cases, the ratings of the

vehicles would have changed by 2 or more stars. When we compared the

risks of serious injury (the base unit categorized into the five star ratings)

derived from the manufacturer and NCAP data, we found that each star

category was associated with a wide band in which the resultant risk

scores of subsequent tests might fall. For example, the results of a second

test of a vehicle rated as 4 stars by its first test could fall between 5 stars

and 2 stars.

The analyses described above are based on the only two sources of

information we could find. The quantity of data in each analysis was not

enough for us to fully quantify the reliability of crash test results; however,

we were able to determine that NCAP scores, whether reported in raw HIC

and chest acceleration scores or as categories of injury probability, have

associated levels of imprecision and that seemingly large differences in

crash test results may not necessarily reflect true differences in a vehicle’s

safety potential. By not properly defining and publishing the degree of

reliability, consumers may be misled into purchasing a vehicle purported

to be more crashworthy than another when, in fact, it may be no more

safe, or even less safe, than the comparison vehicle.

NCAP Results and

Real-World Fatality Rates

Since NCAP crash tests are designed to simulate full-frontal collisions, we

restricted our analysis to those types of crashes and found the results of

NCAP crash tests are generally reflected in real-world fatality rates. That is,

on the whole, a statistically significant relationship exists between

real-world highway fatality rates associated with vehicles tested in the

NCAP program and their scores in crash tests. However, we concluded that

this relationship derives mainly from the high fatality rates of vehicles with

the worst NCAP scores. When we divided vehicles into NCAP score

quintiles—that is, placed the vehicles into one of five 20-percentile

categories based on their location in the distribution of NCAP results—we

found that the quintile with the worst NCAP scores (those vehicles in the

Page 7 GAO/PEMD-95-5 Department of Transportation Crash Tests
B-250144 

highest 20-percentile category) had significantly higher fatality rates than

the remaining 80 percent of NCAP-tested vehicles. The remaining four

quintile categories, however, had associated fatality rates that were not

significantly different from one another. (See figure 2 and appendix VI.)

Figure 2: Mean NCAP Injury Risk

Scores and Fatality Ratesa Fatality Rate

0

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

.093 .140 .192 .307 .723

Mean Injury Risk Score

aBy quintile, per 100,000 vehicles.

Conclusions Over time, the mean risk of injury in frontal crashes, as measured by NHTSA

crash tests, has declined and indeed has mirrored a similar trend in the

annual number of highway fatalities. While we cannot state with certainty

that NHTSA crash tests are a causal factor in improved crashworthiness, we

believe that efforts on the part of automobile manufacturers to produce

vehicles that score well on these tests have contributed to the

improvement of the overall safety of vehicles. At the very least, the results

of NCAP and compliance tests provide indications that the vehicle fleet, on

the whole, has become safer over the past 15 years.

These trends in the mean score of crash tests, however, do not necessarily

suggest that individual vehicles have well-defined levels of safety, nor do

they suggest that the relative rankings of two vehicles would be the same

Page 8 GAO/PEMD-95-5 Department of Transportation Crash Tests
B-250144 

if subsequent trials were conducted. They also do not suggest that

differing test results are reflected in data derived from real-world traffic

collisions. Indeed, only the poorest performers in NCAP had associated

fatality rates that were significantly different than other NCAP vehicles.

Recommendations On the basis of our findings, we make two recommendations to the

Administrator of NHTSA. First, we recommend that information on NCAP

reliability be updated and made available, in clear language, to the general

public. Such an effort would require an update of the repeatability study

the agency conducted in 1984 and could result not only in a better

understanding of the reliability of crash tests for predicting injury risk, but

also in discovering ways in which NHTSA can limit the error that derives

from sources under its control.

We also recommend that NHTSA explore the feasibility of alternative means

of testing the crashworthiness of new vehicles. Computer simulations may

provide one such alternative. It may be possible to better assess the safety

potential of a vehicle through computer-based modeling as this allows

more trials, more quickly, and modeling is capable of simulating impacts at

all points of a vehicle. In addition, this rapidly emerging technology has

the added capability of providing immediate insights into redesigning

vehicles in which the crashworthiness may not yet be optimal.

Agency Comments We received written comments on a draft of this report from the

Department of Transportation. The Department concurred with our

recommendation that it update its information on NCAP reliability. We are

concerned, however, that the agency might believe it has already complied

with this recommendation by developing the star rating format. As noted

above and explained in detail in appendix V, this new format does not

resolve our questions concerning NCAP reliability.

The Department interpreted our second recommendation as a

recommendation to augment or replace “live” crash tests with computer

simulations and did not concur with us. The Department cited concerns

about the costs and predictive limitations of such simulations. We share

these concerns, but we believe the Agency has misinterpreted the

recommendation. We avoided recommending the adoption of any

particular substitute for the current crash test procedures at this time.

Rather, we urged the Agency to explore all possible means of reliably

defining vehicle crashworthiness. Computer modeling is a potential

Page 9 GAO/PEMD-95-5 Department of Transportation Crash Tests
B-250144 

alternative that deserves exploration and monitoring as the technology

matures. Other alternatives could include extending testing programs to

include side, rear, and frontal-offset impacts to gain a better understanding

of the total safety of a vehicle or seeking greater sharing of crash test data

developed by automotive manufacturers either through crash tests

replicating NHTSA’s or through their individual component testing

programs.

The Department provided a number of other specific comments. They are

reproduced in appendix VII, together with our response. We have also

made modifications to the report as we deemed appropriate on the basis

of these comments. After responding to our draft report, the Department

also provided us with additional data relevant to NCAP reliability. The

results of our analysis of these data can be found in appendix V.

We are sending copies of this report to the Secretary of Transportation,

the Administrator of the National Highway Traffic Safety Administration,

and to other interested parties. We will also make copies available to

others upon request. If you have any questions or would like additional

information, please call me at (202) 512-3092. Major contributors to this

report are listed in appendix VIII.

Kwai-Cheung Chan

Director for Program Evaluation

 in Physical Systems Areas

Page 10 GAO/PEMD-95-5 Department of Transportation Crash Tests
Page 11 GAO/PEMD-95-5 Department of Transportation Crash Tests
Contents

Letter 1

Appendix I 

Department of

Transportation Crash

Test Programs

16

Introduction 16

Compliance Test Program 16

New Car Assessment Program 18

Comparison of the Two Tests 18

Appendix II 

Crash Test

Measurement and

Reporting

20

Crash Test Measurements 20

Reporting NCAP Test Results 21

Appendix III 

Anthropomorphic

Test Devices

24

Introduction 24

Comparison of Hybrid II and Hybrid III 24

Appendix IV 

Trends in Crash Test

Results

30

Changes in NCAP Injury Risk Over Time 30

Changes in FMVSS 208 Injury Risk Over Time 33

Appendix V 

Reliability of NCAP

Results

37

Appendix VI 

Methodology for

Analyzing the

Predictive Validity of

NCAP

42

Introduction 42

Relationships Between NCAP and NASS Data 42

Relationships Between NCAP and Fatality Rates 47

Page 12 GAO/PEMD-95-5 Department of Transportation Crash Tests
Contents

Appendix VII 

Comments From the

Department of

Transportation

50

Appendix VIII 

Major Contributors to

This Report

70

Bibliography 71

Tables Table II.1: Maximum Allowable Scores on FMVSS 208 Crash

Tests for Vehicle Compliance

21

Table II.2: Star Ratings and Their Combined Injury Probability

Ranges

23

Table III.1: Mean HIC and Chest Acceleration Scores From NCAP

Tests for Hybrid II and Hybrid III Dummies

27

 Table III.2: Mean HIC and Chest Acceleration Scores From

Compliance Program Tests for Hybrid II and Hybrid III Dummies

28

Table V.1: Mean HIC Scores From NHTSA’s Repeatability Test

and NCAP Results for Vehicles of Similar Weight

38

Table V.2: Number of Vehicles Within Star Rating Categories,

Driver Position

39

Table V.3: Number of Vehicles Within Star Rating Categories,

Passenger Position

40

Table VI.1: Logistic Regression Predicting Hospitalization or

Death in Single-Car Frontal Crashes, Unweighted Sample

44

Table VI.2: Logistic Regression Predicting Hospitalization or

Death in Two-Car Frontal Crashes, Unweighted Sample

45

Table VI.3: Logistic Regression Predicting Hospitalization or

Death in Single-Car Frontal Crashes, Weighted Sample

46

Table VI.4: Logistic Regression Predicting Hospitalization or

Death in Two-Car Frontal Crashes, Weighted Sample

46

Table VI.5: Mean Combined Injury Risk Scores and Fatality Rates

for All Body Styles

49

Table VI.6: Z-scores of Differences Between Mean Fatality Rates

of Combined Injury Risk Quintiles

49

Page 13 GAO/PEMD-95-5 Department of Transportation Crash Tests
Contents

Figures Figure 1: Mean NCAP Injury Risk by Model Year 5

Figure 2: Mean NCAP Injury Risk Scores and Fatality Rates 8

Figure III.1: Instrumentation in the Hybrid II and Hybrid III and

the Cartesian and Anatomical Coordinates

26

Figure IV.1: Mean NCAP Combined, Head, and Chest Injury Risks

by Model Year

30

Figure IV.2: Mean NCAP Head Injury Risk, With and Without Air

Bags

31

Figure IV.3: Mean NCAP Chest Injury Risk, With and Without Air

Bags

32

Figure IV.4: Mean FMVSS 208 Injury Risk by Model Year 33

Figure IV.5: Mean FMVSS 208 Head Injury Risk, With and Without

Air Bags

34

Figure IV.6: Mean FMVSS 208 Chest Injury Risk, With and

Without Air Bags

35

Figure V.1: Risk of Serious Injury, With Estimated Confidence

Interval, by NCAP Star Rating

41

Abbreviations

AAAM Association for the Advancement of Automotive Medicine

DOT Department of Transportation

FARS Fatal Accident Reporting System

FHWA Federal Highway Administration

FMVSS Federal Motor Vehicle Safety Standards

HIC Head injury criterion

ISO International Standards Organization

NASA National Aeronautics and Space Administration

NASS National Accident Sampling System

NCAP New Car Assessment Program

NHTSA National Highway Traffic Safety Administration

SAE Society of Automotive Engineers

SUDAAN Survey Data Analysis

Page 14 GAO/PEMD-95-5 Department of Transportation Crash Tests
Page 15 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix I 

Department of Transportation Crash Test

Programs

Introduction The Department of Transportation has four offices that conduct

automobile crash tests: three within NHTSA and one in the Federal Highway

Administration. A compliance test program conducted by NHTSA’s Office of

Vehicle Safety Compliance consists of full-frontal crashes of automobiles,

light trucks, and vans into a fixed rigid barrier to ensure that vehicles meet

certain minimum safety requirements.1

 Also under the authority of NHTSA is

the New Car Assessment Program, conducted by the Office of Market

Incentives. NCAP tests are similar to compliance tests, but they are

performed to provide consumer information on the relative

crashworthiness of automobiles. The NHTSA Office of Crashworthiness

Research conducts a variety of tests to study a wide range of individual

safety issues that arise from specific crash configurations. Finally, FHWA

conducts crash tests to study the interaction between automobiles and

roadside obstacles and devices such as guard rails, telephone poles, and

bridge abutments.

In this study, we focused on the crash tests run under the compliance

program and the New Car Assessment Program because both tests are

similarly configured, employ standardized procedures, and have been

assessing vehicle crashworthiness over a period of years. The tests

conducted by the Office of Crashworthiness Research and those of FHWA,

although important, have different purposes from those of our study and

could not provide a quantity of data sufficient for us to assess

relationships between test results and real-world performance.

Compliance Test

Program

Section 103 of the National Traffic and Motor Vehicle Safety Act of 1966

charged DOT with establishing standards for vehicle safety. These safety

standards are codified by NHTSA in the U.S. Code of Federal Regulations at

49 C.F.R. Part 571: Federal Motor Vehicle Safety Standards (FMVSS),

Standard No. 208: Occupant Crash Protection. Beginning with the 1987

vehicle model year, FMVSS 208 required that passenger cars, light trucks,

and vans sold in the United States be certified as meeting minimal safety

levels as measured by anthropomorphic dummies in dynamic crash tests.2

The purpose of this standard is

1

Because these tests are required by NHTSA under standard 208 of the Federal Motor Vehicle Safety

Standards, they are commonly called FMVSS 208 tests. NHTSA also uses dynamic crash tests to

determine vehicular compliance with FMVSS 212, Windshield Mounting; FMVSS 219, Windshield Zone

Intrusion; and FMVSS 301, Fuel System Integrity.

2

Self-certification in a 30 mile-per-hour barrier collision and passive restraint requirements were

phased in between 1987 and 1990 for passenger cars. Light trucks, vans, and sport utility vehicles were

required to meet dynamic crash requirements beginning with the 1992 model year.

Page 16 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix I 

Department of Transportation Crash Test

Programs

“to reduce the number of deaths of vehicle occupants, and the severity of injuries, by

specifying vehicle crashworthiness requirements in terms of forces and accelerations

measured on anthropomorphic dummies, and by specifying equipment requirements for

active and passive systems.”

These crash tests are conducted under the guidance of NHTSA’s Office of

Vehicle Safety Compliance.

Sample Selection for

Compliance Tests

The current compliance program relies, for the most part, on a

certification process in which the manufacturer of a specific make and

model vehicle states that the vehicle meets all safety requirements set

forth in FMVSS 208. In addition, each year NHTSA selects a number of

vehicles to test to ensure that the manufacturer’s certification is justified.

The criteria used to determine which specific makes and models to test

are based on whether a vehicle is in its first or second model year, whether

safety features have been added or redesigned, and how many units are on

the road. In selecting models for testing, NHTSA also includes any evidence

of poor crashworthiness derived either from consumer complaints filed

about specific models or from other crash test programs (in particular,

NCAP). Through these criteria, NHTSA compiles a preliminary list of about 50

candidate vehicles for testing and requests information on crash test

performance from the manufacturer of each candidate model to determine

the final list of vehicles to be tested. Though they are under no obligation

to do so, manufacturers will normally provide one or two sets of results

from their tests of the model NHTSA specifies. NHTSA uses these data not

only as an input for determining the final list of test vehicles, but also as a

baseline with which to compare its own results.

Test Conditions The compliance test consists of a full-frontal collision of a vehicle into a

fixed rigid barrier at a velocity of 30 miles per hour. Anthropomorphic test

dummies, fitted with instrumentation to measure forces and accelerations

acting on the head, chest, and both femurs, are placed in the driver and

front passenger seats. Only passive restraint systems—those that require

no effort on the part of an occupant—are engaged. Examples of these are

air bags and automatic seat belts. Seat belts that require active

participation by the occupant are not used.3

 The underlying assumption is

that if a vehicle meets the standards for those occupants who do not make

3

This requirement applies to all passenger cars and those light trucks certified by the manufacturer as

meeting the automatic occupant protection requirement and will be phased in for light trucks

beginning with the 1995 model year.

Page 17 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix I 

Department of Transportation Crash Test

Programs

use of all available safety restraint systems, it will also meet the

requirements for those who do.

The test conditions further specify the forward placement of the seat, the

angle of the seat back, the angle of the steering column (where the vehicle

has tilt steering), and a number of other components. Some of these, such

as adjustable backs for seats, are placed in the manufacturer’s nominal

design riding position—that is, the position the manufacturer says is the

proper one for the average adult male (5 feet 9 inches, 167 pounds).

New Car Assessment

Program

A second crash test program we studied is the New Car Assessment

Program conducted by NHTSA’s Office of Market Incentives. This program

was mandated under title II of the Motor Vehicle Information and Cost

Savings Act of 1972 to provide consumers with an understanding of the

relative crashworthiness of passenger motor vehicles. Since 1979, NCAP has

conducted almost 500 crash tests of passenger cars, light trucks, and vans.

From 1979 to 1986, NCAP was considered an indicant test for vehicle

compliance with Federal Motor Vehicle Safety Standards 212, Windshield

Mounting; 219, Windshield Zone Intrusion; and 301, Fuel System Integrity.

That is, if a vehicle performed reasonably well on these tests, which

required dynamic testing, then it would likely meet compliance test

requirements because the NCAP test involves a more violent crash than the

one required for the compliance test. If a vehicle performed poorly, the

information would be transmitted to the Office of Vehicle Safety

Compliance for testing its compliance with the safety standards. NCAP has

not been an indicant program since the implementation of dynamic crash

tests in the FMVSS 208 program in 1987; however, poor performance on the

NCAP test typically leads to compliance testing of the same model.

Comparison of the

Two Tests

The NCAP crash test is generally similar to the compliance test. Both are

full-frontal collisions into a fixed rigid barrier, and both use roughly the

same criteria when determining which vehicles to test. However, three

very important differences distinguish the two test programs. First,

vehicles in the NCAP test are crashed at 35 miles per hour rather than 30

miles per hour, the velocity in the compliance test. This 5 mile-per-hour

difference results in a 36-percent increase in the amount of energy in the

system.4

4

Kinetic energy is a function of mass and velocity (Ek = 1/2 mv2). The additional energy in the NCAP

test over the compliance test derives from the square of the velocity when the mass of the vehicle is

held constant. Thus (35 miles per hour)2 is 36-percent greater than (30 miles per hour)2.

Page 18 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix I 

Department of Transportation Crash Test

Programs

Second, all active as well as passive safety belts in the automobile are used

in the NCAP test; that is, the test dummies are restrained by any manual seat

belt furnished with the vehicle as well as any automatic belt or air bag. In

the compliance test, as noted earlier, only passive restraints (automatic

belts and air bags) are used.

The third and foremost difference between the two programs is the

underlying purpose of the tests. NCAP is a market-based program that

disseminates information to consumers on the relative safety of passenger

vehicles. There are no minimum allowable safety performance criteria that

vehicles must meet, although NCAP collects the same measurements as the

compliance test. Despite the fact that NCAP is not a compliance program,

industry personnel have expressed the opinion that the NCAP test has

become the de facto regulation. That is, failure to meet compliance levels

on this more stringent test involving a more forceful collision than the

official compliance test could imply that a vehicle is unsafe. Currently,

nearly all vehicles tested under NCAP meet the safety requirements

specified in FMVSS 208.

Page 19 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix II 

Crash Test Measurement and Reporting

Crash Test

Measurements

Both the compliance and NCAP tests use anthropomorphic test dummies to

collect data related to injury potential by measuring accelerations and

forces placed on an occupant’s head, chest, and upper leg.1

 Specific levels

for each measure, established under FMVSS 208, represent upper-bound

limits for compliance with vehicle safety requirements. These ceilings

were designed to correspond to the level at which there is a one-in-six

chance of an occupant’s sustaining an injury that poses a serious threat to

life.

The head injury criterion, the measure used in crash tests to assess

potential head injury, was adopted by NHTSA on the basis of research

conducted to establish the likelihood of skull fractures under different

velocity changes. HIC is measured as a composite of the axial accelerations

of the head (in three dimensions). Specifically, HIC is the product of (1) the

2.5 power of the average of the resultant head acceleration over a time

interval not more than 36 milliseconds and (2) that time interval. The

equation for the function is

HIC [1/(t2 t1) adt]2.5(t2 t1).

A HIC score of 1,000, the highest allowable score for achieving vehicle

compliance, is associated with a one-in-six chance of sustaining a serious

skull injury.

For determining potential injury to the chest region, chest acceleration is

measured in gravitational units (g’s).2

 The potential for injury to the chest

skeletal structure is measured by the actual resultant peak tridimensional

acceleration of the upper thorax. Compliance with FMVSS 208 for this

measure is set at 60 g’s over 3 milliseconds, an acceleration level that has

been associated with four or more fractured ribs.

Depending on the type of crash test dummy used, a second chest

measurement, termed chest compression, is taken. (See appendix III.) This

measures the amount of reduction in the distance between the sternum

and the spinal column and is determined to assess the likelihood of injury

to internal organs. Currently, only one of the two types of crash test

dummies (Hybrid III) is capable of measuring this, and the choice of which

dummy type to use in a test (either compliance or NCAP) is made by the

1

Acceleration is the rate of change in velocity with respect to time, while force is the rate of change in

velocity with respect to time for a given mass.

2

One g is equal to 32 feet/second2, or 9.8 meters/second2.

Page 20 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix II 

Crash Test Measurement and Reporting

manufacturer of the test vehicle. If the Hybrid III is used in a compliance

test and the vehicle exceeds the 3-inch maximum reduction distance

allowed (the limit associated with major lacerations to the spleen or

kidneys), the vehicle is considered not to be in compliance with FMVSS 208.

The final measure taken in both the compliance and NCAP tests is the

compressive force transmitted axially through the upper legs (femurs).

The femur tolerance level of 2,250 pounds of force is based primarily on

experimental impacts to the lower limbs and is associated with a

one-in-six chance of sustaining a fracture to that bone.

When the results of a compliance test exceed the limit for any of the

measures, an investigation is conducted to determine reasons for the

failure and is typically accompanied by a recall or remedy campaign. If a

determination of noncompliance is made, the model being tested may not

be sold in the United States. This differs from NCAP as its tests are not

conducted to assess vehicle compliance with federal regulations, and

therefore, no punitive actions may be taken by NHTSA should a vehicle

exceed any of the limits. Table II.1 lists the four measurements made in

both test programs and presents the maximum allowable scores under

compliance testing for each measure.

Table II.1: Maximum Allowable Scores

on FMVSS 208 Crash Tests for Vehicle

Compliance Measure

Maximum

allowable score

Head injury criterion 1,000

Chest acceleration 60 g’s

Chest compressiona 3 inches

Femur load 2,250 pounds

aThis measure applies to the Hybrid III dummy only. (See appendix III.)

Reporting NCAP Test

Results

In 1978 (for the 1979 model year), NHTSA began testing about 30 vehicles

per year through its New Car Assessment Program. While no manufacturer

is required to exceed 30 mile-per-hour standards, the program, using a 35

mile-per-hour crash test, is designed to inform customers of the relative

crashworthiness of an automobile. Traditionally, NCAP reported the actual

HIC, chest acceleration, and femur load scores with a disclaimer that only

vehicles within 500 pounds of each other could legitimately be compared.

Also, NCAP would cite the compliance ceiling levels (1,000 HIC, 60-g chest

acceleration, and 2,250-pound femur load) as representing a one-in-six

Page 21 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix II 

Crash Test Measurement and Reporting

chance of sustaining a severe injury. Despite NHTSA’s claim of overall

success in providing information about how well or how poorly passenger

vehicles protect their occupants in crashes, some critics argued that NCAP’s

method of reporting test results left consumers confused.

In response to fiscal year 1992 Senate Appropriations Committee

requirements, NHTSA performed a user study and began implementing new

methods of informing consumers of the comparative levels of the safety of

passenger vehicles as measured by NCAP. This new method, a star chart

rating system, is designed to provide consumers with a quick, simplified,

single point of comparison to evaluate vehicles in the NCAP test.3

Based upon analyses of a variety of accident injury studies, NHTSA

developed a scale, known as the “Level of Protection Scale,” that relates

the probability of sustaining an injury to the level of protection a vehicle

provides its occupants from receiving such an injury.4

 This scale forms the

basis of NHTSA’s star chart method for releasing NCAP test results to the

public. The star chart, which NHTSA began using in December 1993, reports

a range of 1 to 5 stars, with 5 stars indicating the best crash protection for

vehicles within the same weight class.

The number of stars a vehicle may be rated is derived from the injury

probabilities associated with the HIC and chest g scores obtained in the

crash tests. These probabilities are calculated using the following

formulas:

 Phead = [1 + exp(5.02 - 0.00351 x HIC)]-1

 Pchest = [1 + exp(5.55 - 0.0693 x Chest Acceleration)]-1

 Pcombined = Phead + Pchest - (Phead x Pchest)

A vehicle is then assigned a star rating based on its combined injury risk,

with the specific number of stars determined by the range in which the

3

The star chart rating system applies only to vehicles tested in NCAP. In compliance tests, the actual

HIC, chest acceleration, and femur load results are reported, as the primary purpose of the test is

vehicular compliance to safety regulations and not a comparative assessment of the likelihood of

occupants’ sustaining serious injuries in different vehicle models.

4

In SAE Paper No. 851246, “The Position of the United States Delegation to the International Standards

Organization (ISO) Working Group 6 on the Use of HIC in the Automotive Environment,” P. Prasad and

H. Mertz presented an injury risk function curve (which this scale is based upon) that relates the

probability of a severe head injury to HIC.

Page 22 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix II 

Crash Test Measurement and Reporting

combined injury risk lies. The ranges for each star rating are shown in

table II.2.

Table II.2: Star Ratings and Their

Combined Injury Probability Ranges

Rating

Range of

probability

5 stars 0 - .10

4 stars + .10 - .20

3 stars + .20 - .35

2 stars + .35 - .45

1 star + .45 - 1.00

Page 23 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix III 

Anthropomorphic Test Devices

Introduction Currently, two types of anthropomorphic test dummies are used in both

the compliance and NCAP tests: the Hybrid II and Hybrid III 50th-percentile

male dummies. Requirements for both types of dummies used in

compliance testing are specified in 49 C.F.R. Part 572: Anthropomorphic

Test Dummies.1

 The design and performance criteria specified for each

dummy type

“are intended to describe a measuring tool with sufficient precision to give repetitive and

correlative results under similar test conditions and to reflect adequately the protective

performance of a vehicle or item of motor vehicle equipment with respect to human

occupants.”2

In this appendix, we discuss the characteristics and instrumentation of the

Hybrid II and Hybrid III 50th-percentile anthropomorphic test dummies,

under the provisions of the NHTSA standards pertaining to occupant crash

protection. We also provide a comparison of the two dummy types’

performance in NCAP and the compliance test programs. Finally, we

summarize the 1993 decision to standardize the test dummy, requiring the

mandatory use of the Hybrid III in all NHTSA crash test programs beginning

in 1997.

In both the compliance and NCAP test, the manufacturer of the vehicle

being tested has the option to choose which type of dummy will be used.

While both dummies are designed to represent the physical characteristics

of the average adult male, important differences between them exist.

Despite the differences, the requirements for vehicular conformance to

FMVSS 208 are not different for the two instruments, with the exception of

the chest compression criterion, which applies only when the Hybrid III

dummy is used.

Comparison of Hybrid

II and Hybrid III

Differences in

Construction

Part 572 of the Federal Motor Vehicle Safety Standards specifies the types

of anthropomorphic dummies to be used in the FMVSS 208 compliance test.

Currently, two specific types of anthropomorphic test dummies may be

used in a compliance crash test: the Hybrid II and the Hybrid III. As

1

NCAP is not required to follow the standards in part 572; nonetheless, it does.

2

49 CFR Ch. V (10-1-91 Edition), Part 572-Anthropomorphic Test Dummies, p. 581.

Page 24 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix III 

Anthropomorphic Test Devices

specified in subpart B of 49 C.F.R. part 572, since 1973 the Hybrid II

50th-percentile male test dummy is 5 feet 9 inches tall and weighs

approximately 164 pounds, and until 1986, this dummy was used when

determining compliance to FMVSS 208. In 1986, 49 C.F.R. parts 571 and 572

were amended to adopt the Hybrid III 50th-percentile dummy as an

alternative to the Hybrid II for FMVSS testing. This gave manufacturers the

option of using either the Hybrid II or Hybrid III test dummy as the means

of determining a vehicle’s conformance to NHTSA’s performance

requirements. Like its predecessor, the Hybrid III is 5 feet 9 inches tall but

weighs slightly more (167 pounds). Also, like the Hybrid II, each Hybrid III

used in a compliance test must meet the specifications and performance

criteria of part 572 before and after each vehicle test in order to be an

acceptable compliance tool.

The Hybrid II and Hybrid III use the same instrumentation in the head,

chest, and femurs. (See figure III.1.) However, according to General

Motors, developer of the Hybrid III, its 50th-percentile male dummy was

designed to improve on Hybrid II technology and biofidelity.3

 Most experts

regard the Hybrid III test dummy as more biofidelic than the Hybrid II,

having a more human-like seated posture, as well as head, neck, chest, and

lumbar spine designs. The Hybrid III’s responses to crash conditions more

closely approximate the motions associated with human anatomy in crash

situations and, therefore, more accurately evaluate injury risks. For

example, the improved flexibility of the Hybrid III’s neck over the Hybrid

II allows researchers a greater ability to assess the injury potential of

whipping motions.

In addition to the greater biofidelity, the experts we interviewed stated

that the Hybrid III is more sophisticated technologically than the Hybrid II

because it has more instrumentation for measuring potential injuries.

Specifically, the Hybrid III is capable of measuring nearly four times as

many forces and accelerations throughout the body as the Hybrid II. For

example, not only does the Hybrid III measure injury potential to the

skeletal structures, but it can also determine injury potential to the soft

tissues in the upper thorax through the chest compression measure.

Further, the Hybrid III has accelerometers and load cells placed in the

neck and lower legs that can measure the potential for injuries caused to

those anatomical areas. To date, no criteria have been established for

meeting compliance for the additional measures other than chest

compression. However, the measures do provide DOT with additional

3

The biofidelity of a test dummy is mainly assessed by comparisons of its response to those of

cadavers under the same test conditions.

Page 25 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix III 

Anthropomorphic Test Devices

information on the potential physiological responses associated with

vehicular crashes.

Figure III.1: Instrumentation in the Hybrid II and Hybrid III and the Cartesian and Anatomical Coordinatesa

aReprinted with permission from SAE publication R-103, copyright 1990, Society of Automotive

Engineering, Inc.

Differences in Test Results Currently, the determination of which dummy to use in a test is made by

the manufacturer of the vehicle being tested. Through 1993, manufacturers

chose to use the Hybrid III in 36 of the 133 tests of passenger cars in the

compliance program and in 30 of the 86 tests of passenger cars in NCAP

since the dummy became available for use in the two programs (1988 and

Page 26 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix III 

Anthropomorphic Test Devices

1990, respectively). One expert hypothesized that the reason so few

compliance tests involve Hybrid III dummies is that they tend to receive

higher HIC scores, especially in noncontact situations and that there is no

guarantee that a car designed around the Hybrid II will pass a test using a

Hybrid III.

The differences between the dummies used in NHTSA’s tests, described

above, led us to compare the driver-side HIC and chest acceleration scores

from passenger-car compliance and NCAP tests in an attempt to quantify

the potential effects on test reliability such differences could create. In this

analysis, we controlled for the presence of a driver-side air bag in the car.

In general, we found the Hybrid III dummy scores were lower than the

Hybrid II scores, but that the presence of air bags strongly affects the

relative performance of the two dummy types. (See tables III.1 and III.2.)

Table III.1: Mean HIC and Chest

Acceleration Scores From NCAP Tests

for Hybrid II and Hybrid III Dummiesa Measure

Hybrid II Hybrid III

Score

Number of

tests Score

Number of

tests

HIC 793 56 637 30

Air bag 695 27 511 24

No air bag 903 29 1,141 6

Chest acceleration (g’s) 50.7 56 47.1 30

Air bag 50.5 27 46.5 24

No air bag 50.9 29 49.3 6

aFor passenger cars from 1990 to 1993, with and without air bags.

Specifically, we found that

• Vehicles tested with Hybrid III dummies had lower HIC and chest

acceleration scores than those tested with Hybrid II dummies in both

compliance and NCAP tests. In NCAP tests, Hybrid III dummies averaged 156

HIC and 3.6 g’s less than Hybrid II dummies. (See table III.1) Similarly, in

compliance tests, the mean head injury criterion score for cars tested with

Hybrid III dummies was 97 HIC lower than the score for tests that used the

Hybrid II, while the mean chest acceleration score was about 2 g’s less for

test cars that used the Hybrid III. (See table III.2)4

• In both the NCAP and compliance tests, Hybrid III had significantly lower

HIC scores than Hybrid II dummies in vehicles equipped with air bags. In

vehicles without air bags, Hybrid IIIs had significantly higher HIC scores

4

All differences except for chest scores in compliance tests were statistically significant (p < .05).

Page 27 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix III 

Anthropomorphic Test Devices

than Hybrid IIs. The difference could occur because of the greater

flexibility of the Hybrid III’s neck.5

• In both the NCAP and compliance tests, Hybrid III dummies had

significantly lower chest acceleration results than Hybrid II dummies in

cars with air bags. There was little difference between the chest scores of

Hybrid III and Hybrid II dummies in cars without air bags.

Table III.2: Mean HIC and Chest

Acceleration Scores From Compliance

Program Tests for Hybrid II and Hybrid

III Dummiesa

Measure

Hybrid II Hybrid III

Score

Number of

tests Score

Number of

tests

HIC 487 97 390 36

Air bag 482 47 268 25

No air bag 492 50 667 11

Chest acceleration (g’s) 45.4 97 43.3 36

Air bag 48.4 47 43.8 25

No air bag 42.6 50 42.3 11

aFor passenger cars from 1988 to 1993, with and without air bags.

Manufacturers have been reluctant to use Hybrid III dummies for tests of

cars not equipped with air bags because these dummies tend to produce

higher HIC results, especially in cases where the dummy’s head did not

contact the interior components of the car. (Only 18 percent of

compliance tests of cars without air bags from 1988 to 1993 and 18 percent

of NCAP tests of cars without air bags from 1990 to 1993 used the Hybrid

III.) Industry representatives stated that because HIC was developed to

determine potential skull injuries—a condition that will not occur if the

head does not contact the vehicle’s interior—it should be applied only to

cases in which the head actually makes contact. Although they agree that

brain injuries can occur when the head does not contact the interior, they

contend that the instrumentation in the dummy’s head does not measure

the potential for these types of injuries. Therefore, they conclude that in

cases of “noncontact” HICs, the results are meaningless and misleading.

Thus, rather than risk a spuriously higher HIC score in either the

compliance or NCAP tests, manufacturers have tended to use the Hybrid II

for vehicles that do not have air bags.

5

Because the neck of the Hybrid III is more flexible, it offers less resistance to motion. Assuming two

identical crash tests with the same amount of energy in each system, the Hybrid III’s head will move

through its forward arc of motion (flexion) at a greater velocity than the Hybrid II until it reaches the

end of that arc, when it rapidly decelerates.

Page 28 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix III 

Anthropomorphic Test Devices

While these complex interactions of dummy type, safety equipment, and

test conditions can be explained by biomechanical differences between

the Hybrid II and Hybrid III dummies, they may also be explained by

differences in the test vehicles themselves. As we noted earlier, the

manufacturers specify which dummy type to use in NHTSA crash tests, and

one may assume that, in the absence of other motivations, they would

choose the dummy they anticipate will yield more favorable results.

Exclusive Use of the

Hybrid III

As noted above, each manufacturer undergoing a compliance test may

specify either the Hybrid II or the Hybrid III test device. But in recent

years, NHTSA has become more convinced that using the Hybrid III will help

ensure that all new vehicles are designed with the benefit of the most

human-like test dummy available. NHTSA regards the Hybrid III as more

representative of human responses in frontal crashes, and it can monitor

more types of potential injuries as well. Further, NHTSA has come to

recognize that exclusive use of the Hybrid III for compliance testing under

FMVSS 208 would result in greater comparability of test results among

vehicles produced by different manufacturers.

For these reasons, the agency recently issued a Notice of Final Rule that

requires the exclusive use of the Hybrid III for all compliance testing under

standard no. 208.6

 The final rule takes effect September 1, 1997, to

coincide with the date at which all passenger cars and 80 percent of light

trucks must be equipped with air bags and all light trucks must have

passive (automatic) restraint systems. NCAP will also switch to exclusive

use of the Hybrid III test dummy beginning with the 1996 model year.

These modifications to the two programs will create a greater degree of

standardization of crash tests, thereby, in NHTSA’s view, increasing the

“comparability of test results among vehicles produced by different

manufacturers, particularly those that now use different dummy types.”7

6

On Nov. 8, 1993, NHTSA published the final rule (Notice 83, 58 Fed. Reg. 59189), which requires the

use of the Hybrid III test dummy for all compliance testing under standard no. 208, to be effective Sept.

1, 1997.

7

DOT, NHTSA, 49 C.F.R. Part 571: Federal Motor Vehicle Safety Standards; Occupant Crash Protection;

58 Fed.Reg. 214, Nov. 8, 1993, p. 59189.

Page 29 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix IV 

Trends in Crash Test Results

Changes in NCAP

Injury Risk Over Time

We conducted analyses of the trends in NCAP test scores from 1979 through

1993 and found that scores have both improved and become more uniform

during the period. We have expressed NCAP results in terms of the

combined injury risk scores to which NCAP now translates its HIC and chest

scores to produce its new “star system”.1

 Figure IV.1 shows the mean

injury risks for the driver position, by year, for model years 1979 through

1993.

Figure IV.1: Mean NCAP Combined, Head, and Chest Injury Risks by Model Yeara

Injury Risk

0

0.1

0.2

0.3

0.4

0.5

0.6

1979 1981 1983 1985 1987 1989 1991 1993

Model Year

Chest Injury Risk

Head Injury Risk

Combined Risk

aFor all passenger cars. Does not include light trucks and vans.

The mean combined injury risk decreased significantly from a high of

0.507 in 1980 to a low of 0.190 in 1993. The figure also indicates that the

significant reduction in the combined risk derives from a significant and

consistent decrease in the mean head injury risk probability. While the

mean chest injury risk declined significantly during the period, it has been

1

For a complete discussion of the derivation of risk scores and star ratings see appendix II.

Page 30 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix IV 

Trends in Crash Test Results

relatively stable since 1983. The variation between the individual test

results has also decreased over the years. For example, NCAP head injury

criterion scores for vehicles in 1979 ranged from 521 HIC to 4,513 HIC,

whereas in 1993, the range was between 273 HIC and 1,459 HIC.

One reason for the decline in the mean combined injury risk and its

accompanying variation over time is the increasingly widespread

installation of air bags. Cars equipped with air bags had significantly lower

head injury risk probabilities than cars without air bags. (See figure IV.2.)

Since the first NCAP test of cars equipped with air bags in 1987, these

vehicles have scored an average head injury risk of 0.063, while cars

without air bags have averaged 0.216.

Figure IV.2: Mean NCAP Head Injury Risk, With and Without Air Bagsa

aFor passenger cars with and without driver-side air bags. Does not include light trucks and vans.

Before 1987, no test vehicle was equipped with an air bag, and only one 1987 model-year test

vehicle was equipped with an air bag.

Page 31 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix IV 

Trends in Crash Test Results

There is little difference, however, between the mean chest injury risks for

passenger cars equipped with air bags (0.108) and those that did not

employ this type of restraint (0.120). (See figure IV.3.) Given the relatively

flat chest injury risk shown in figure IV.1, it appears that this risk factor,

regardless of the type of restraint, has contributed little to the declining

trend for the combined injury risk.

Figure IV.3: Mean NCAP Chest Injury Risk, With and Without Air Bagsa

aFor passenger cars with and without driver-side air bags. Does not include light trucks and vans.

Before 1987, no test vehicle was equipped with an air bag, and only one 1987 model-year test

vehicle was equipped with an air bag.

Page 32 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix IV 

Trends in Crash Test Results

Changes in FMVSS

208 Injury Risk Over

Time

We also conducted similar analyses for passenger cars tested in the

compliance program. Despite fluctuations from year to year, the combined

injury risk did not change significantly from 1987 to 1993.2

 (See figure

IV.4.)

Figure IV.4: Mean FMVSS 208 Injury

Risk by Model Yeara Injury Risk

0

0.1

0.2

0.3

0.4

0.5

0.6

1987 1989 1991 1993

Model Year

Chest Injury Risk

Head Injury Risk

Combined Risk

aFor all passenger cars. Does not include light trucks and vans.

2

Though the compliance program does not report scores in terms of risk, we translated the results to

risk probabilities to give the reader a base scale from which to compare the differences in scores that

might result from the differences in the velocities and restraint usage in the two crash test programs.

Page 33 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix IV 

Trends in Crash Test Results

During the same period a steady, though not statistically significant,

decline in the mean head injury risk was offset by a significant increase in

the mean chest injury risk. These opposing trends are associated with the

increased installation of air bags, which are associated with lower head

injury risk probabilities and higher chest injury risk probabilities for

compliance tests. (See figures IV.5 and IV.6.)

Figure IV.5: Mean FMVSS 208 Head

Injury Risk, With and Without Air Bagsa

aFor passenger cars with and without driver-side air bags. Does not include light trucks and vans.

Before 1988, no test vehicle was equipped with an air bag.

Page 34 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix IV 

Trends in Crash Test Results

Figure IV.6: Mean FMVSS 208 Chest

Injury Risk, With and Without Air Bagsa

aFor passenger cars with and without driver-side air bags. Does not include light trucks and vans.

Before 1988, no test vehicle was equipped with an air bag.

The contrasting chest injury risk results between NCAP and compliance

programs may have occurred because of the differences in the

configuration of the two tests—largely from the determination of which

restraint systems are used. In an NCAP crash that makes use of all available

passive and manual restraint systems, the seat belt absorbs the dummy’s

kinetic energy over a gradual period (for a crash event) before the dummy

contacts the air bag. However, cars with air bags are not required to have

automatic seat belts. And since manual seat belts are not engaged in

compliance tests, the dummy in the driver position is not likely to be

restrained by a safety belt in compliance tests of cars with air bags. The

dummy, therefore, is likely to move forward without a reduction in its

kinetic energy, resulting in a more forceful collision with the air bag than if

a seat belt was also in use. Over time, as more of the vehicles tested in the

compliance program came equipped with air bags, the mean compliance

chest score increased.

Page 35 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix IV 

Trends in Crash Test Results

This is not to say that an air bag-equipped vehicle is less safe than one that

does not have an air bag. Indeed, the chest g results of cars with air bags

may not be directly comparable to those without the devices because the

distribution of the force loading on the chest is different for air bags than

for safety belts. Air bags distribute the load caused by chest contact across

a larger surface area than safety belts. Nevertheless, the higher chest g

result for an air bag-equipped vehicle is consistent with the view held by

many traffic safety experts that safety belts alone (that is, without air

bags) are much more effective than airbags alone (that is, without safety

belts).3

The decreasing mean crash test results parallel a similar trend with annual

fatalities, and part of that latter trend can rightfully be attributed to NHTSA

crash tests. In discussions with industry representatives, we found that

automobile manufacturers attempt to design vehicles to meet compliance

levels for frontal collisions in the NCAP test, as well as ensure that all other

safety criteria are met. In addition to “live” crash tests, manufacturers use

computer models of frontal collisions, rear and side impacts, and roof

crush to simulate NHTSA crash tests and to ensure that the cars meet NHTSA

standards. The types of simulations range from models of specific

components of the vehicle to nonlinear finite-element models, which

incorporate all specifications of the automobile and can predict

interactions between the car and its occupants during a collision. These

simulations allow manufacturers to gain insight into the deformation of

the vehicle, likely intrusions into the occupant compartment, and the force

loads generated by various structural components. Though computersimulated crashes are expensive because they generally require access to a

supercomputer, they do allow manufacturers to gain knowledge of how

the car will perform and how to correct problems before building

prototypes. They are also much less costly and less time-consuming than

building and crashing prototypes. In addition, one simulation expert stated

that the results of finite-element simulations generally reflect the results

obtained in actual crash tests and that the industry uses crash tests in part

to validate its computer-based crash models.

3

The relative protection afforded by safety belts and airbags is discussed in Highway Safety: Causes of

Injury in Automobile Crashes (GAO/PEMD-95-4; May 1995).

Page 36 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix V 

Reliability of NCAP Results

Our analyses of the trends in NCAP test results have shown that (1) injury

risk probabilities have declined over time and (2) the variation between

test results has lessened over time. (See appendix IV.) It would seem that

cars have become more crashworthy—at least as measured by NCAP—and

that this improved crashworthiness is more uniformly distributed across

the passenger car fleet. Indeed, in 1979 the combined injury risk for

NCAP-tested vehicles ranged from 0.106 to 1.0 (rounded), whereas in 1993,

the ends of the distribution ranged from 0.096 to 0.581. Despite the

decreased variation in test results, however, the difference between the

highest and lowest risk probabilities is still substantial.

This variation is open to two quite different interpretations. It may indicate

the sensitivity of crash tests to real differences between vehicle models, or

it may reflect the imprecision of the test scores. In classical measurement

theory, reliability is defined as the repeatability of test results. The

reliability of crash tests would be estimated by comparing the results from

repeated crash tests of the same model vehicle.

On only one occasion has NHTSA attempted to determine whether NCAP

crash test results are, in fact, reproducible by crashing a single model on

multiple occasions. In this study, 12 consecutively manufactured 1982

Chevrolet Citations were crash-tested by three test facilities, with each

facility testing four vehicles, in an attempt “to quantify the degree of

variation, as well as develop generalized statistical conclusions about test

repeatability.”1

 The mean HIC score for the 12 tests was 685, with the

scores ranging from 495 HIC to 954 HIC. NHTSA identified several sources of

variation in results derived from the test procedure, as well as from the

testing facilities, the test instrumentation, the test dummy used, and the

individual vehicles. NHTSA could not quantify the amount of variation

attributable to each of these five areas because of the number of possible

sources of error within each.

Although the amount of variation that can be attributed to any of the

sources of error is incalculable, the confounding interactions of

accumulated error lead to questions about the reliability of NCAP results.

The variation between different units was artificially constrained by

selecting 12 consecutively manufactured Chevrolet Citations, yet the head

1

John M. Mackey and Charles L. Gautier, Results, Analysis and Conclusions of NHTSA’s 35 MPH

Frontal Crash Test Repeatability Program, SAE Paper No. 840201 (Warrendale, Pa.: SAE, 1984), p. 74.

Page 37 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix V 

Reliability of NCAP Results

injury results still had a range of 459 HIC.

2

 This variation among the HIC

scores implies that two scores with a range of less than 219 are not, in

statistical terms, significantly different and that any score between 781 HIC

and 1,219 HIC is not significantly different from 1,000.3

Table V.1 illustrates how this level of reliability could affect the

interpretation of other crash test scores. The table displays the mean HIC

score from the 12 Citation crash tests and the HIC scores of four other

vehicles of similar weight.4

 It also indicates whether the NCAP HIC scores

are significantly different from (1) the mean Citation score and (2) the

putative ceiling of 1,000.5

 The HIC scores received by all the vehicles except

the 1990 Lexus are significantly lower than 1,000. However, there is no

statistically significant difference between the mean HIC score received by

the Citation and three of the four other vehicles.

Table V.1: Mean HIC Scores From

NHTSA’s Repeatability Test and NCAP

Results for Vehicles of Similar Weighta

Significantly different from

Vehicle

Curb weight

(pounds) HIC

1982

Citation HIC = 1,000

1982 Chevrolet Citation 3,260 685 b Yes

1988 Oldsmobile Delta 88 3,460 710 No Yes

1990 Lexus ES250 3,280 992 Yes No

1991 Ford Taurus 3,290 480 No Yes

1991 Chrysler New Yorker 3,310 511 No Yes

aFrom NHTSA’s 12 1982 Chevrolet Citation tests and NCAP results for vehicles of similar weight.

bDoes not apply.

2

This constraint was imposed by NHTSA to limit, as far as possible, sources of error outside the test

process itself. The results of the 12 tests, however, revealed differences in the crush of the test

vehicles, for example. (The “crush” is the distance by which the car is collapsed by the collision—from

the front of the car moving rearward.) Thus, error derived from the manufacturing of the vehicles still

influenced the overall variation among tests, but NHTSA could not quantify its influence.

3

These ranges derive from a calculation of a 95-percent confidence interval using the mean and

standard deviation of the results from NHTSA’s repeatability study. A similar study of seven 1983

Volvo 760 GLEs conducted by the manufacturer revealed a somewhat narrower, though still

substantial, range in HIC scores (from 697 to 1,004) and indicated that two HIC scores with a range of

as much as 147 are not significantly different.

4

NHTSA cautions that scores from vehicles more than 500 pounds different are not necessarily

comparable.

5

For these comparisons, we assume that the other models would demonstrate the same HIC score

variations in multiple crash tests as the Citation. While this assumption may be subject to debate, we

have no other data from which to form a different assumption. We use HIC scores here rather than

combined injury risk since the chest g scores from the test were unavailable.

Page 38 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix V 

Reliability of NCAP Results

After reviewing a draft of this report, NHTSA provided us with a second set

of data that could shed additional light on the reliability of NCAP scores.

These data represent the results of crash tests of model-year 1991 through

1994 vehicles conducted by automobile manufacturers in tests that

essentially duplicate the NCAP test conditions. The data were voluntarily

submitted to NHTSA before planned NCAP tests.

We compared the manufacturer scores with those obtained from NCAP

after translating them into the single injury probability score that serves as

the basis for NHTSA’s recently introduced star rating system. (See appendix

II.) We found that a statistically significant first-order correlation exists

(r = .72) between the two sets of injury risk probabilities.

We then compared the distributions of star ratings derived from NCAP and

manufacturers’ tests. Table V.2 compares the star ratings for the driver

position, and table V.3, for the passenger position. If agreement between

the two sets of tests had been perfect, all events in the tables would have

fallen on the diagonals from upper left to lower right. In actuality, star

ratings are the same for approximately one-half of the vehicle models

tested (55 percent for the driver position and 45 percent for the passenger

position). Differences of one or more stars exist between manufacturer

and NCAP ratings for about one-half of the tests; 8 percent of the vehicle

models have differences of two or more stars.

Table V.2: Number of Vehicles Within Star Rating Categories, Driver Position

Manufacturer star rating

NCAP star rating 1 star 2 stars 3 stars 4 stars 5 stars Total

1 star 6 0 3 3 0 12

2 stars 0 1 3 1 0 5

3 stars 1 1 16 14 0 32

4 stars 0 1 15 37 6 59

5 stars 0 0 0 6 5 11

Total 7 3 37 61 11 119

Page 39 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix V 

Reliability of NCAP Results

Table V.3: Number of Vehicles Within Star Rating Categories, Passenger Position

Manufacturer star rating

NCAP star rating 1 star 2 stars 3 stars 4 stars 5 stars Total

1 star 2 1 1 2 0 6

2 stars 1 0 3 3 0 7

3 stars 1 2 8 23 1 35

4 stars 1 0 10 33 6 50

5 stars 0 0 0 11 10 21

Total 5 3 22 72 17 119

As appendix II explains, each of NHTSA’s star ratings represents a range of

injury probability. For example, a rating of 4 stars indicates that in a crash

situation similar to that tested by NHTSA the probability of serious injury to

an individual is between 1 in 10 and 2 in 10. The solid bars in figure V.1

depict these probability ranges for each star rating. The lines attached to

the bars represent “confidence intervals” that we estimated from the

standard deviation of the absolute difference between the combined injury

risks for drivers derived from manufacturer and NCAP tests. These

confidence intervals represent the estimated range of injury probability

within which a vehicle with a nominal rating could be expected to vary if

tested again. For example, a 4-star rating could be associated with a

vehicle with a “true” injury probability between zero and 0.363. This range

overlaps the confidence intervals associated with the 5- and 2-star ratings.

Our estimates of the reliability of NCAP crash tests are based on the only

two sources of relevant information we are aware of: the repeated crashes

of the 1982 Chevrolet Citation, and a comparison of manufacturer and

NCAP test scores from 1991 to 1994. Neither of these sources provides ideal

information for precisely quantifying the measurement error associated

with NCAP scores. We do not know how well the results of the Citation

experiment can be applied to vehicles manufactured and crash-tested 10

years later. While the manufacturer-NCAP comparison applies to a large

number of late-model cars, we cannot be sure how well the manufacturers

succeeded in replicating NCAP crash test conditions in each case or to what

extent the results from other manufacturer tests varied from the ones

reported to NHTSA.

Page 40 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix V 

Reliability of NCAP Results

Figure V.1: Risk of Serious Injury, With Estimated Confidence Interval, by NCAP Star Ratinga

aConfidence interval is based on 1.96 standard deviations of the absolute difference between the

combined injury risk scores derived from manufacturer and NCAP tests of the same vehicle

model.

Nevertheless, both analyses support the same conclusion that NCAP scores,

whether reported in raw HIC and chest acceleration scores or as categories

of injury probability, have associated levels of imprecision. As a result,

substantial differences in scores between two test results (100-200 HIC, or a

1-star—or possibly 2-star—rating difference) may not represent true

differences in crashworthiness.

Page 41 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VI 

Methodology for Analyzing the Predictive

Validity of NCAP

Introduction The overall purpose of both the compliance and NCAP crash tests is to

determine the crashworthiness, or safety, of passenger vehicles. This

implies, therefore, that a relationship exists between the results of crash

tests and real-world injuries and fatalities. To examine this issue, we

conducted two analyses comparing results derived from NCAP tests to

those from national accident databases.1

 Specifically, our analysis

compared NCAP results with traffic injury and fatality information from the

National Accident Sampling System (NASS) and the Fatal Accident

Reporting System (FARS). This appendix details the methodologies and

results of both analyses.

Relationships

Between NCAP and

NASS Data

Data from the National Accident Sampling System for 1988 through 1991

were combined to determine whether the results of New Car Assessment

Program tests are good predictors of serious injuries and fatalities in

real-world automobile crashes. The NASS is a sample of annual

police-reported accidents involving passenger cars, light trucks, and vans

that had to be towed because they were damaged. The NASS year

corresponds to the calendar year rather than the automobile industry’s

model year, and emphasis is placed on the most recent 5 model-year

vehicles. We chose this data system for two reasons: (1) It is a national

database that contains information on all types of automobile collisions,

and (2) it is the only national database that reports a vehicle’s change in

velocity (delta v)—the best available indicator of accident

severity—resulting from the collision.

We reduced the NASS data sets to single-vehicle and two-vehicle accidents

and then combined them into one data set. This resulted in a total of

14,253 vehicles in the final data set. We then matched the results of the

NCAP crash tests to the vehicles in our NASS file. NCAP results from 1983

through 1992 were chosen for the analysis for two reasons: (1) We

assumed that crash test results are applicable for a given time (as cars age,

their crashworthiness may decrease owing to wear and tear) and (2) NASS

data were available for the calendar years 1988 through 1991. Because NASS

emphasizes for inclusion collisions involving vehicles from the 5 most

recent model years, we chose 5 years as the period of time at which a test

score no longer applies; therefore, NCAP scores from 1983 were the earliest

1

For these analyses, we decided to use results only from NCAP for two reasons. First, NCAP has been

crash-testing vehicles since 1979 and had conducted about 340 tests of passenger cars through 1992.

The compliance program has been in existence only since 1987 and had conducted only 145 tests.

Second, presumably because of the higher velocity used in the NCAP tests, the results of NCAP tend to

vary to a greater extent than those of the compliance program, and a large portion of vehicles tested in

NCAP have HIC and chest acceleration scores in excess of the ceiling values of 1,000 and 60 g’s,

respectively, while these scores tend to cluster far below the ceiling values for the compliance tests.

Page 42 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VI 

Methodology for Analyzing the Predictive

Validity of NCAP

we included in the analysis. In addition, each NASS year has a half-year’s

data from the following model year, as the model year usually begins in

late summer. Therefore, the 1991 NASS had some accidents involving 1992

model-year automobiles.

The NCAP results were matched to the NASS data set on the following

criteria: the make of the vehicle (that is, the manufacturer), the model, the

model year, and the body type (sedan, convertible, and so forth). In cases

in which a specific make, model, model year, and body type were tested

on more than one occasion, only the first test was used. Results for models

with corporate twins (vehicles with platforms identical to one another but

sold under different model names—for example, Ford Taurus and Mercury

Sable) were projected to the twins. The resultant data set for our analyses

contained 1,985 cases. When weighted by NASS sampling weights, these

represented more than 9 million accidents.

We conducted logistic regression analyses to determine whether a

relationship exists between serious injuries and fatalities in actual

automobile collisions and results from crash tests conducted for NCAP. We

analyzed crashes in which damage to the right front, left front, or full front

of the vehicle occurred. Single-car and two-car crashes were examined

separately.2

 We conducted two sets of analyses: one on the unweighted

sample in our dataset and a second, which incorporated the NASS sampling

weights.3

Our analyses of the relationship between real-world traffic injuries and

fatalities and NCAP injury risk probabilities were limited to drivers of

passenger cars (two-door and four-door sedans, coupes, hatchbacks, and

convertibles).4

 We restricted our analyses to “restrained” drivers—that is,

drivers who made proper use of either a manual or an automatic seat belt

or whose air bag deployed during the crash.

The dependent variable used in the analyses was constructed from NASS

injury codes to represent whether the driver of an NCAP passenger car

involved in a crash either died or was hospitalized for at least 1 day

2

“Two-car crashes” refers to collisions between two passenger cars, or a passenger car tested in NCAP

and either a light truck or van as defined by the NASS.

3

To analyze the weighted sample, we used the Survey Data Analysis (SUDAAN) statistical package,

which takes into account the stratification and unequal selection probabilities inherent in the sampling

design of NASS.

4

Although we included light trucks and vans in determining the sample for two-car collisions, we

analyzed the relationship between NCAP scores and traffic injuries and fatalities for passenger cars

only.

Page 43 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VI 

Methodology for Analyzing the Predictive

Validity of NCAP

specifically because of the crash. This was coded as a dichotomous

variable, with those who died or were hospitalized receiving a 1 and all

other nonmissing values receiving a zero. The independent variable of

interest was the combined injury risk score associated with specific

vehicle models as derived from the HIC and chest acceleration scores from

NCAP tests. (See appendix II.) However, because characteristics of the

driver and the vehicle and, most importantly, the severity of the crash (as

measured by the total change in velocity, or delta v) are associated with

the likelihood of injuries and fatalities, we included occupant

characteristics (age, gender), vehicle characteristics (curb weight and, in

two-car crashes, the weight of the other vehicle), and crash severity (delta

v) in our logistic regression models.5

Tables VI.1 and VI.2 present the results of our analyses of the unweighted

sample for one- and two-car crashes. The predictive power of delta v

dominates both models, but the driver’s age and the car’s weight also

appear as significant predictors of injury in two-car crashes. In these

crashes, older drivers and drivers of lighter cars were more likely to suffer

injury or death. In neither model was the NCAP injury risk significantly

related to hospitalization or death in either one-or two-car crashes.

Table VI.1: Logistic Regression

Predicting Hospitalization or Death in

Single-Car Frontal Crashes,

Unweighted Samplea

Variable Beta

Standard

error

Wald

statistic

Significance

level

Injrisk –6.8337 5.0594 1.8243 .1768

Age 0.0004 0.0245 0.0002 .9883

Gender 0.2689 0.4369 0.3790 .5381

Curbwgt –0.1021 0.1404 0.5287 .4672

Dvtotal 0.1580 0.0567 7.7579 .0053

Constant 0.4380 3.9979 0.0120 .9128

Legend

Injrisk = Driver injury risk

Age = Age of driver

Gender = Gender of driver

Curbwgt = Vehicle’s curb weight

Dvtotal = Total change in velocity (mph)

aRepresents 46 restrained drivers.

5

See Highway Safety: Have Automobile Weight Reductions Increased Highway Fatalities? (GAO/

PEMD-92-1; Oct. 1991); Highway Safety: Factors Affecting Involvement in Vehicle Crashes (GAO/

PEMD-95-3; Oct. 1994); and Highway Safety: Causes of Injury in Automobile Crashes (GAO/ PEMD95-4; May 1995).

Page 44 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VI 

Methodology for Analyzing the Predictive

Validity of NCAP

Table VI.2: Logistic Regression

Predicting Hospitalization or Death in

Two-Car Frontal Crashes, Unweighted

Samplea

Variable Beta

Standard

error

Wald

statistic

Significance

level

Injrisk 1.2413 1.0302 1.4519 .2282

Age 0.0430 0.0142 9.1362 .0025

Gender –0.0782 0.2388 0.1072 .7434

Curbwgt –0.1689 0.0611 7.6327 .0057

Othvehwgt –0.0014 0.0338 0.0017 .9671

Dvtotal 0.2311 0.0516 20.0368 .0000

Constant –2.7524 1.8460 2.2231 .1360

Legend

Injrisk = Driver injury risk

Age = Age of driver

Gender = Gender of driver

Curbwgt = Vehicle’s curb weight

Othvehwgt = Weight of other vehicle

Dvtotal = Total change in velocity (mph)

aCollisions with vehicles weighing less than 10,000 pounds. Represents 131 restrained drivers.

Tables VI.3 and VI.4 present the findings from the weighted sample and

show very similar results to the unweighted sample. The strongest

predictor remains the crash severity, and in two-car crashes, driver age is

related to collision outcomes. The weighted sample presents two different

conclusions from the unweighted sample, however. The curb weight of the

vehicle falls short of statistical significance by traditional criteria, and

more to the point, a significant relationship between NCAP risk scores and

death or hospitalization appears.

Page 45 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VI 

Methodology for Analyzing the Predictive

Validity of NCAP

Table VI.3: Logistic Regression

Predicting Hospitalization or Death in

Single-Car Frontal Crashes, Weighted

Samplea

Variable Beta

Standard

error

Wald

statistic

Significance

level

Injrisk –14.2980 11.2770 1.6075 .2230

Age –0.0300 0.0332 0.8135 .3804

Gender 0.4028 1.5665 0.0661 .8004

Curbwgt –0.2023 0.1546 1.7118 .2092

Dvtotal 0.2672 0.0690 15.0409 .0013

Constant 2.3599 6.3191 0.1395 .7137

Legend

Injrisk = Driver injury risk

Age = Age of driver

Gender = Gender of driver

Curbwgt = Vehicle’s curb weight

Dvtotal = Total change in velocity (mph)

aRepresents 8,401 restrained drivers.

Table VI.4: Logistic Regression

Predicting Hospitalization or Death in

Two-Car Frontal Crashes, Weighted

Samplea

Variable Beta

Standard

error

Wald

statistic

Significance

level

Injrisk 3.2379 1.3351 5.8817 .0275

Age 0.0635 0.0200 10.0933 .0059

Gender 0.9361 0.6075 2.3752 .1429

Curbwgt –0.1298 0.0702 3.4238 .0828

Othvehwgt –0.0433 0.0587 0.5435 .4717

Dvtotal 0.2860 0.0891 10.3078 .0055

Constant –7.1838 2.6253 7.4875 .0146

Legend

Injrisk = Driver injury risk

Age = Age of driver

Gender = Gender of driver

Curbwgt = Vehicle’s curb weight

Othvehwgt = Weight of other vehicle

Dvtotal = Total change in velocity (mph)

aCollisions with vehicles weighing less than 10,000 pounds. Represents 23,514 restrained drivers.

Some degree of doubt must be associated with these findings because of

the nature of the sample on which they are based. NASS uses a highly

complex stratified sampling design to achieve national representativeness

for its relatively small sample of observations. The NASS database we used

contained 21,377 observations, which when properly weighted, represent

Page 46 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VI 

Methodology for Analyzing the Predictive

Validity of NCAP

more than 9 million accidents. Unfortunately, we found only 366 instances

of NCAP-tested cars that met our criteria of properly restrained drivers, and

only about one-third of these could be used because of missing values on

one or more variables. This drastic reduction in sample size, when

combined with the highly uneven distribution of missing values across

sampling strata, makes the sampling weight associated with any

observation of doubtful validity.

Relationships

Between NCAP and

Fatality Rates

To overcome the statistical limitations of our NASS database, we turned to

the Fatal Accident Reporting System (FARS). By using FARS, we looked to

substantially increase the number of usable cases in the analysis in that

FARS contains information on all accidents in a given year that involve at

least one fatality (about 45,000 cases per year), while NASS contains only a

sample of all accidents (about 3,000 cases per year). In addition, we

reasoned that while FARS lacks the information on crash severity provided

by NASS’ estimate of the total change in velocity, its severity of crashes was

relatively homogeneous because the database is restricted to

fatal—presumably severe—crashes.

For this analysis, only passenger cars from the 1982 to 1991 model years

were included.6

 In addition to the actual test vehicles, our analysis

included vehicles that had no substantial structural changes in model

years following the tested model year. That is, if a 1984 model-year vehicle

were tested in NCAP and no structural changes were made to the 1985

version of the vehicle and it was not retested, the 1985 model year was

assigned the same combined injury risk score as the 1984 vehicle.

We then matched the vehicles to the FARS and the R.L. Polk Vehicle

Registration System (Polk) databases based on the make (that is, the

manufacturer), model, model year, and body type of the vehicle. The FARS

database is a compilation of all automobile accidents in the United States

in any given calendar year in which at least one fatality occurred. The Polk

system is a database that contains information on the types, numbers and

weights of vehicles registered in a given calendar year. Data for both

systems are for the calendar years 1987 through 1991. As with the analysis

of NASS data, we restricted this analysis to one- and two-car frontal

collisions in which the driver of the NCAP-tested vehicle was restrained by

either a seat belt or an air bag.

6

Convertibles, light trucks, vans, and multipurpose vehicles were excluded from the analysis.

Page 47 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VI 

Methodology for Analyzing the Predictive

Validity of NCAP

Having matched the NCAP vehicles to the FARS and Polk systems, we then

calculated the fatality rates for the vehicles. This was done simply by

dividing the number of fatalities by the number of registered vehicles. The

fatality rates in our analysis are expressed in terms of fatalities per 100,000

registered vehicles.

We then correlated the driver combined injury risk scores and fatality

rates associated with vehicle models in a number of ways. First, we

calculated a simple correlation using just information on those elements.

Next, we regressed fatality rates on additional characteristics associated

with vehicles using a Poisson model, which allows one to compare rates of

individual cases, especially when the sample size is moderately large and

the probability of an event occurring is either very low or very high. This

type of analysis fit our needs in that a large number of cases (884) were

included in our analyses while the fatality rates of the vehicles included

were low (overall, there were 1,036 deaths for approximately 19 million

registered vehicles).

The variables added to the model held information on the model year and

body style of the vehicles in the dataset. We controlled for the model year

as a proxy for certain driver, vehicle, and roadway characteristics that

could not be included in the model. We controlled for the body style for

two reasons: (1) as a surrogate for the relationships found between

specific body styles and certain driver characteristics and (2) as a rough

surrogate for the weight of the vehicle.7

As a final analysis, we divided the NCAP injury risk distribution into

quintiles and compared the fatality rates of the different groups. Each

quintile represented one-fifth of the passenger cars tested in NCAP from

1982 to 1991.

We found that a first-order correlation between NCAP injury risk and

fatality rates exists (p = .007). When information on the body style and

model year of the vehicle was included in the analysis, the strength of the

relationship increased (p = .001). However, the relationship appears to be

the result of the high fatality rates associated with the poorest performers

in NCAP. Indeed, vehicle models within the highest quintile of injury risk

(those in the highest 20 percent of the distribution) had significantly

higher fatality rates than all other quintile categories. Further, we found

that the worst performers on the NCAP test had injury risk probabilities

7

For a discussion of vehicle and driver characteristics associated with accident involvement, see

Highway Safety: Factors Affecting Involvement in Vehicle Crashes (GAO/PEMD-95-3, Oct. 1994).

Page 48 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VI 

Methodology for Analyzing the Predictive

Validity of NCAP

approximately eight times higher than the best-scoring cars, while their

fatality rates were almost 28 percent higher. The remaining four quintile

groups, on the other hand, were not significantly different from one

another. (See tables VI.5 and VI.6.) Thus, it seems that the relationship

between driver fatality rates and predicted injury risk stems from the

significantly higher fatality rates associated with vehicles that have very

high NCAP injury risk probabilities.

Table VI.5: Mean Combined Injury Risk

Scores and Fatality Rates for All Body

Stylesa Quintile

Mean combined

injury risk (NCAP)

Fatality rate

(FARS/Polk)

1 .093 .503

2 .140 .577

3 .192 .573

4 .307 .497

5 .723 .642

aFatality rate calculated by dividing the number of fatalities in a given risk quintile by the total

number of registered vehicles in that quintile. Fatality rates are expressed as fatalities per 100,000

registered vehicles. The mean combined injury risk is the average NCAP injury risk for the

quintile. Body styles include coupes, sedans, two- and four-door hatchbacks, and station

wagons.

Table VI.6: Z-Scores of Differences

Between Mean Fatality Rates of

Combined Injury Risk Quintilesa

Comparison quintile

Z-score

Quintile 12345

1 b .363 .224 .813 2.745

2 -.363 b -.150 .520 2.684

3 -.224 .150 b .635 2.690

4 -.813 -.520 -.635 b 2.119

5 –2.745 –2.684 –2.690 –2.119 b

aMean fatality rates as reported in table VI.5. A z-score of 1.96 or greater shows significant

differences between the means at a probability level of at least p = .05.

bNot applicable.

Page 49 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

Note: GAO comments

supplementing those in the

report text appear at the

end of this appendix.

Page 50 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

Page 51 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

See comment 1.

See comment 2.

See comment 3.

Page 52 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

See comment 4.

See comment 5.

Page 53 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

See comment 6.

See comment 7.

See comment 8.

Page 54 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

See comment 1.

See comment 9.

Now p. 4.

See comment 10.

Page 55 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

Now p. 16.

Now p. 17.

Now p. 18.

See comment 11.

Page 56 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

Now p. 21.

Now p. 20.

Deleted.

Term changed.

Now appendix III.

Page 57 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

Now p. 27.

Now pp. 26-29.

Deleted.

Now p. 29.

See comment 12.

Now pp. 35-36.

Page 58 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

Now pp. 35-36.

Now pp. 37-38.

See comment 2.

Now p. 38.

See comment 2.

Now pp. 39-41.

See comment 6.

Now p. 42.

Now pp. 42-43.

See comment 13.

Page 59 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

Now pp. 44-47.

See comment 9.

See comment 4.

Now p. 5.

See comment 14.

See comment 6.

Page 60 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

Now p. 37.

Now p. 49.

Now p. 29.

Now pp. 21-23.

Now pp. 42-47.

See comment 15.

Page 61 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

Now pp. 44-47.

See comment 4.

Now pp. 45-46.

See comment 16.

Now pp. 47-49.

See comment 17.

See comment 18.

Now pp. 47-49.

See comment 17.

Page 62 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

See comment 19.

Page 63 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

The following are GAO’s comments on the letter from the Department of

Transportation dated July 13, 1994.

GAO Comments 1. We agree with NHTSA that the terms “reliability” and “validity,” as used in

the report, refer to their statistical meanings, test repeatability, and

predictive validity, respectively. We share the concern that common usage

of the terms “could have damaging effects” on NCAP’s credibility and

mislead a casual user to conclude that the tests have not had positive

effects on the crashworthiness of the U.S. passenger car fleet. For this

reason, we have modified the subtitle of the report.

NHTSA is correct in asserting that we use the term reliability in its

traditional meaning of reproducibility. We disagree with NHTSA’s

implication that this meaning is not relevant to “the relative safety

performance of vehicles.” Indeed, as our report indicates, the band of

uncertainty that surrounds crash test scores (as it does any test results)

can affect the relative ranking of vehicles.

2. We recognize that model lines would have NCAP result variations unique

to themselves, and the report clearly states this caveat (see p. 38, footnote

5). After completing the Citation experiment, NHTSA made changes in its

test procedures to improve their reliability. Unfortunately, no equivalent

test of how effective these changes were in reducing the variability

between test scores was subsequently performed.

After NHTSA had provided its official comments on our draft report, the

agency also provided us with crash test results from automobile

manufacturers for model-year 1991 through 1994 vehicles. These data were

provided to NHTSA in preparation for tests conducted under NCAP and were

results of tests that essentially duplicated the NCAP testing procedure. The

agency had previously declined to provide this information because they

considered it proprietary. We analyzed these data and have included our

findings in the body of the report (see pp. 39-41). Though this information

cannot define the boundaries of NCAP reliability, the difference between

manufacturer and NCAP results reinforces our conclusion that the

reliability of NCAP results is limited.

3. We do not disagree with NHTSA that rigorous protocols for crash testing

are followed and that NHTSA verifies the results of the crash test with

high-speed film. However, this process merely verifies that the

accelerometers placed in the test dummy accurately recorded the data

Page 64 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

from the specific trial. It does not address the issue of reliability, which in

classic statistical theory holds that test data are reliable if consistent

results are obtained through repeated trials of an experiment using

specific procedures. In the case of NCAP crash testing, a specified

procedure exists, but the model of the test vehicle changes. Unless

multiple trials of the same model line are conducted, we cannot determine

the reliability of test results.

We are sensitive to the costs the Agency could incur in addressing our

recommendation that it update and publish, in clear language, its

knowledge of the reliability of NCAP results. For this reason, we suggest

that the Agency explore alternative means for accomplishing this goal, in

particular by making use of the knowledge base developed by

manufacturers. Regardless of the method the Agency uses to address the

recommendation, its purpose will not be, as NHTSA suggests, to “enhance

the scientific reliability of its data” or “narrow its standard deviation,” but

to assure American consumers that they are provided with accurate

information about the relative crashworthiness of vehicles.

4. We agree that NHTSA has found a statistically significant difference

between the fatality risk of belted drivers involved in two-car frontal

collisions in cars with “good” NCAP performance and those that were

“poor” performers. In our analysis of the fatality rates, though using a

different methodology, we found similar results.

The analyses we performed shared a common weakness with NHTSA’s;

namely, they were both limited to a relatively small proportion of

real-world crashes. NHTSA’s estimate of reduced fatality risk for better

scoring NCAP cars is derived from analyses using only two-car crashes in

which both drivers were belted and at least one occupant was killed.

These conditions limited their analyses to between 81 and 170 crashes.

(NHTSA’s database was drawn from the 1979 through 1991 FARS years, which

represent between 40,000 and 50,000 highway fatalities annually.)

Our analysis was also limited to NCAP cars involved in fatal accidents with

restrained drivers, although we also included single-vehicle crashes and

FARS data from 1987 through 1991. These limitations reduced our sample to

884 cars. Both NHTSA and we agree that a statistically significant

correlation between NCAP scores and real-world crashes can be found but,

to use NHTSA’s words, the correlation is “far from perfect.”1

 Our analyses

1

See NHTSA, Correlation of NCAP Performance With Fatality Risk in Actual Head-on Collisions, 1994,

p. xviii.

Page 65 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

suggested that this correlation derived from the fatality rates of the worst

scoring cars, and not from crashworthiness differences among relatively

good NCAP performers.

5. We generally agree with NHTSA’s comment that the improvement in NCAP

scores over time has contributed to an improvement in highway safety.

However, many other influences unrelated to crash testing, such as safety

belt usage laws, and the toughening of drunk driving laws, have also

contributed to this trend.

6. Our report does not address the purported ease of interpretation

associated with the new star rating system. However, we did incorporate

NHTSA’s new reporting system into our analysis of the new data provided us

by NHTSA. Our findings provide detail to support the conclusion of our draft

report: that a reporting system can be no more reliable than the scoring

system on which it is based.

We disagree that the new star rating system “eliminates . . . [the] implied

precision” of HIC, chest, and femur scores. It is true that some cars with

nonsignificant differences in scores would end up in the same category

under the new system, and thus correctly be presented to the public as

roughly equal in crashworthiness. However, it is also true that other cars

with nonsignificant score differences could be placed in different

categories, a scoring artifact that incorrectly implies substantial

differences in the relative levels of crash protection provided by the

vehicles. For example, while a vehicle with a chest g of 40 and a HIC of 550

will receive 5 stars, one with a chest g of 40 and a HIC of 555 will receive 4

stars. We do not believe that this difference in HIC scores implies an actual

crashworthiness difference.

7. NHTSA appears to suggest that it has already complied with this

recommendation through the adoption of its new reporting system. We

disagree. The new system, while seemingly clear, does not communicate

to the public the band of uncertainty associated with star ratings. Our

analyses of the manufacturers’ NCAP test results suggests that this band is

sizable and illustrates its potential effects. However, additional

information needs to be collected and analyzed before the precision of

crash test results can be adequately defined.

8. The recommendation is to explore alternative methods for determining

the crashworthiness of vehicles. We cited computer simulations as one

promising avenue to explore. We recognize the limitations of the current

Page 66 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

capabilities of computer simulations (the high cost of supercomputers, the

complexity of programming, and so on), and we agree with NHTSA that this

technology could not replace actual crash tests in the near future.

However, NHTSA’s comment suggests that it has examined the potential

benefits of this rapidly emerging technology and has dismissed them. We

believe that it should continue to monitor and periodically reassess them.

It appears to us that as the technology develops and becomes less costly,

the potential benefits of such a system extending to a much larger set of

crashes than NCAP now considers at some point in the future may outweigh

its costs.

Other possible approaches include ones that NHTSA is already considering,

such as extending the range of tests to include both side-impact crashes

and frontal-offset crashes. While such tests would expand the applicability

of NCAP tests to a larger portion of real-world events, they would also

substantially increase the costs of the program. This consideration

reinforces our belief that the costs and benefits of alternative approaches

such as computer modeling need to be revisited regularly over the next

decade.

9. We are aware of the limitations of the NASS database, and we agree with

NHTSA that the number of cases that mimic the NCAP configuration are few.

Indeed, in the 4 years of NASS data we analyzed for the project, only 46 of

over 14,000 cases applied to our model most closely resembled the NCAP

configuration.

We disagree that the methodology was inappropriate. The models used in

the analyses were designed not only to simulate the NCAP conditions, but

also to discover the sensitivity of NCAP for predicting other frontal

collisions, and thereby maximize the number of frontal crash

configurations for which the test was applicable and meaningful. It seems

reasonable to expect that, given enough cases, NCAP should predict

real-world traffic injuries and fatalities in collisions that essentially

duplicate the test conditions; however, given the small number of actual

events that apply to this configuration, the meaning of any unweighted

statistically significant relationship is questionable.

10. There is no contradiction between these statements. NCAP’s relative

rankings of different models may be inaccurate in some cases.

Nevertheless, it is unlikely that the parallel improvement in NCAP scores

and highway safety statistics over the past 15 years is totally coincidental.

Page 67 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

11. We agree with NHTSA’s comment about manufacturer participation in

NCAP, and the language has been changed. With respect to the

quasi-regulatory nature of NCAP, manufacturers repeatedly stated that they

must design automobiles to meet this test as if it were the standard. In oral

commentary on our draft report, one NHTSA official pointed out that almost

all passenger cars meet compliance standards in the NCAP test, and that “in

effect, it’s a de facto standard.”

12. The 220-point reduction in the mean HIC falls short of statistical

significance (p = .171). This, we believe, is a function of the low number of

cases and high variations in the early years of compliance testing.

Although the decline is not statistically significant, we would reiterate that,

on average, vehicles tested for compliance with FMVSS 208 tend to have HIC

and chest acceleration scores that are far below the maximum allowable

levels.

13. Although “it has not been proven,” it seems reasonable to assume that

a 1979 vehicle that was involved in an accident in 1991 no longer had the

same level of structural integrity as it did when it was new, owing to the

rusting of the frame, for example, or the weakening of welds. It also seems

reasonable to assume that a 1979 model-year vehicle would not perform at

its full original safety potential in a collision that occurred in 1991.

14. As our report states, and NHTSA cites, no statistical analysis can, by

itself, establish cause-and-effect linkage, and we do not demand this result

of our analyses.

15. We accepted NHTSA’s suggestion and used SUDAAN to perform additional

analyses of the NASS data. The results were inconclusive. In one case

(two-vehicle collisions), we found a statistically significant relationship

between NCAP scores and serious injury. (See table VI.4.) However, this

result could easily be spurious since the application of NASS sampling

weights (which vary substantially and can be quite large) to the small

subset of cases that both fit our criteria and have no missing data can

greatly distort the analysis. If, as NHTSA suggests, a subset of NASS data is

“insufficient to conduct any type of statistical analyses,” applying sampling

weights to a nonrandom selection of variously weighted cases is

potentially misleading.

16. We are aware that in some analyses, NHTSA has used the combination of

subject vehicle weight and its ratio to the other vehicle weight as

predictors of injury instead of simply using the weight of the two vehicles.

Page 68 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VII 

Comments From the Department of

Transportation

We did not feel it necessary to reanalyze the data using weight and weight

ratio since, as NHTSA has pointed out, they “are mathematically equivalent

to the information provided by the two individual vehicle weights.”2

17. We used the traditional adjustment, the ratio of fatalities to the number

of registered vehicles, to correct for the variations in exposure to accident

involvement among the NCAP-tested vehicles. We agree with NHTSA that

other factors, such as driver age and driving history, are also important

predictors of accident involvement and are not captured by this

adjustment. 3

 Our goal here, however, was to answer the simple question:

Are proportionately more drivers killed in poor scoring NCAP cars than in

better scoring cars? Our answer is “yes.”

18. Based on NHTSA’s comment, we converted HIC and chest g scores to the

combined injury probability, which forms the basis for NHTSA’s new rating

system, and used it as a variable in the analyses conducted and presented

in this report.

19. The section is no longer in the report.

2

“NHTSA, A Collection of Recent Analyses of Vehicle Weight and Safety,” 1991, p. 6.

3

See Highway Safety: Factors Affecting Involvement in Vehicle Crashes (GAO-PEMD-95-3; Oct. 1994).

Page 69 GAO/PEMD-95-5 Department of Transportation Crash Tests
Appendix VIII 

Major Contributors to This Report

Program Evaluation

and Methodology

Division

Robert E. White, Assistant Director

David G. Bernet, Project Manager

Edward J. Logsdon, Project Staff

Martin T. Gahart, Project Staff

Dale Harrison, Project Staff

Beverly A. Ross, Project Staff

Venkareddy Chennareddy, Referencer

Page 70 GAO/PEMD-95-5 Department of Transportation Crash Tests
Bibliography

Alem, Nabih M., Guy S. Nusholtz, John W. Melvin. “Head and Neck

Response to Axial Impacts.” Proceedings of the Twenty-Eighth Stapp Car

Crash Conference (SAE Paper No. 841667). Warrendale, Pa.: Society of

Automotive Engineers, 1984. Pp. 275-82.

Association for the Advancement of Automotive Medicine and the

International Research Council on the Biomechanics of Impact. The

Biomechanics of Impact and Motor Vehicle Crash Performance: A Global

Concern—Conference Materials. Des Plaines, Ill.: AAAM, 1993.

Backaitis, Stanley H., ed. Biomechanics of Impact Injury and Injury

Tolerances of the Head-Neck Complex (SAE Book No. PT-93-43).

Warrendale, Pa.: SAE, 1993.

Blalock, Hubert M., Jr. Social Statistics. New York: McGraw-Hill, 1979.

Dixon, Camille M. “Automotive Crashworthiness Rating: Legislation and

Testing.” Proceedings of the Thirtieth Stapp Car Crash Conference (SAE

Paper No. 862046). Warrendale, Pa.: SAE, 1986.

Eiband, A.M. Human Tolerance to Rapidly Applied Accelerations: A

Summary of the Literature (NASA Memorandum No. 5-19-59E). Washington,

D.C.: National Aeronautics and Space Administration, 1959.

Eppinger, Rolf H., and Susan C. Partyka. “Estimating Fatality Reductions

With Safety Improvements.” Proceedings of the Eighth International

Technical Conference on Experimental Safety Vehicles. Washington, D.C.:

U.S. Department of Transportation, National Highway Traffic Safety

Administration, 1980. Pp. 432-38.

Foster, J. King, James O. Kortge, and Michael J. Wolanin. “Hybrid II: A

Biomechanically-Based Crash Test Dummy.” Proceedings of the

Twenty-First Stapp Car Crash Conference (SAE Paper No. 770938).

Warrendale, Pa.: SAE, 1977. Pp. 975-1014.

Fraser, T.M. Human Response to Sustained Acceleration” (NASA-SP-103).

Washington, D.C.: NASA Scientific and Technical Information Division,

1966.

Page 71 GAO/PEMD-95-5 Department of Transportation Crash Tests
Bibliography

Gadd, C.W. “Criteria for Injury Potential.” Impact Acceleration Stress

Symposium, 27-29 November 1961, Brooks AFB, Texas (National Research

Council Pub. No. 977). Washington, D.C.: National Academy of Sciences,

1962. Pp. 141-44.

Gadd, Charles W. “Use of a Weighted-Impulse Criterion for Estimating

Injury Hazard.” Proceedings of the Tenth Stapp Car Crash Conference (SAE

Paper No. 660793). Warrendale, Pa.: SAE, 1966. Pp. 164-74.

General Motors. MVSS: A Guide To Federal Motor Vehicle Safety

Standards & Regulations. Detroit: GM, Environmental Activities, 1989.

Gennarelli, Thomas A. “The State of the Art of Head Injury Biomechanics.”

Proceedings of the Twenty-Ninth Conference of the American Association

for Automotive Medicine. Des Plaines, Ill.: AAAM, 1985. Pp. 447-63.

Gillis, Jack. The Car Book: The Definitive Buyer’s Guide to Car Safety,

Fuel Economy, Maintenance and More, 1993 ed. New York: Harper

Perennial, 1993.

Gurdjian, E.S., et al. “Significance of Relative Movements of Scalp, Skull,

and Intracranial Contents During Impact Injury of the Head.” Journal of

Neurosurgery, 29:1 (1967), 70-72.

Gurdjian, E.S., V.L. Roberts, and L.M. Thomas. “Tolerance Curves of

Acceleration and Intracranial Pressure and Protective Index in

Experimental Head Injury.” Journal of Trauma, 6:5 (1965), 600-04.

Gurdjian, E.S., J.E. Webster, and H.R. Lissner. “Observations on the

Mechanism of Brain Concussion, Contusion, and Laceration.” Surgery,

Gynecology, and Obstetrics, 101:12 (1965), 680-90.

Hirsch, Arthur E., and Rolf H. Eppinger. “Impairment Scaling From the

Abbreviated Injury Scale.” Proceedings of the Twenty-Eighth Conference

of the American Association for Automotive Medicine. Morton Grove, Ill.:

AAAM, 1984. Pp. 209-24.

Hodgson, V.R., L.M. Thomas, and P. Prasad. “Testing the Validity and

Limitations of the Severity Index.” Proceedings of the Fourteenth Stapp

Car Crash Conference (SAE Paper No. 700901). Warrendale, Pa.: SAE, 1970.

Hodgson, Voigt, and L.M. Thomas. “Comparison of Head Acceleration

Injury Indices in Cadaver Skull Fracture.” Proceedings of the Fifteenth

Page 72 GAO/PEMD-95-5 Department of Transportation Crash Tests
Bibliography

Stapp Car Crash Conference (SAE Paper No. 710854). Warrendale, Pa.: SAE,

1971. Pp. 190-206.

Holbourn, A.H.S., and M.A. Edin. “Mechanics of Head Injuries.” Lancet,

245 (1943), 438-41.

Joksch, Hans C. “Velocity Change and Fatality Risk in a Crash—A Rule of

Thumb.” Accident Analysis and Prevention, 25:1 (1993), 103-04.

Jones, Ian S., and R.A. Whitfield. “Predicting Injury Risk With New Car

Assessment Program Crashworthiness Ratings.” Accident Analysis and

Prevention, 20:6 (1988), 411-19.

Jones, Ian S., R.A. Whitfield, and Diane M. Carroll. “New Car Assessment

Program Results and the Risk of Injury in Actual Accidents.” Proceedings

of the Tenth International Technical Conference on Experimental Safety

Vehicles. Washington, D.C.: DOT, NHTSA, 1985. Pp. 371-80.

Koch, M., et al. “Car Model Safety Rating—Further Development Using the

Paired Comparison Method.” Proceedings of the Eighth International

Technical Conference on Experimental Safety Vehicles. Washington, D.C.:

DOT, NHTSA, 1980. Pp. 432-38.

Kornhauser, Murray. Structural Effects of Impact. Baltimore: Spartan

Books, 1964.

Langwieder, K. “Passenger Injuries in Collisions and Their Relation to

General Speed Scale.” Proceedings of the Seventeenth Stapp Car Crash

Conference. New York: SAE, 1973. Pp. 1-34.

Langwieder, Klaus, Maximilian Danner, and Walter Schmelzing.

“Comparison of Passenger Injuries in Frontal Car Collisions With Dummy

Loadings in Equivalent Simulations.” Proceedings of the Twenty-Third

Stapp Car Crash Conference (SAE Paper No. 791009). Warrendale, Pa.: SAE,

1979. Pp. 201-31.

Mackey, John M., and Charles L. Gauthier. Results, Analysis and

Conclusions of NHTSA’s 35 MPH Frontal Crash Test Repeatability Program

(SAE Paper No. 840207). Warrendale, Pa.: SAE, 1984.

McCormick, Earnest James. Human Factors in Engineering and Design.

New York: McGraw-Hill, 1982.

Page 73 GAO/PEMD-95-5 Department of Transportation Crash Tests
Bibliography

Marquardt, James F. “Collision Severity—Measured By V.” Proceedings of

the Twenty-First Conference of the American Association for Automotive

Medicine. Morton Grove, Ill.: AAAM, 1977. Pp.379-90.

Newman, James A. “Head Injury Criteria in Automotive Crash Testing.”

Proceedings of the Twenty-Fourth Stapp Car Crash Conference (SAE Paper

No. 801317). Warrendale, Pa.: SAE, 1980. Pp. 703-47.

Partyka, Susan C. “A Comparison of AIS and ISS Predictions of Fatality on

NCSS.” Proceedings of the Twenty-Fourth Conference of the American

Association for Automotive Medicine. Morton, Grove, Ill.: AAAM, 1980. Pp.

156-69.

Pike, Jeffrey A. Automotive Safety: Anatomy, Injury, Testing and

Regulation. Warrendale, Pa.: SAE, 1990.

Prasad, Priya, and Harold J. Mertz. The Position of the United States

Delegation to the ISO Working Group 6 on the Use of HIC in the Automotive

Environment (SAE Paper No. 851246). Warrendale, Pa.: SAE, 1985.

Salvendy, Gavriel. Handbook of Human Factors. New York: John Wiley &

Sons, 1987.

Society of Automotive Engineers. Crash Avoidance SP-544: International

Congress & Exposition, 1983 (SAE Pub. No. SP-83-544). Warrendale, Pa.:

1983.

Society of Automotive Engineers. Human Tolerance to Impact Conditions

as Related to Motor Vehicle Design (SAE Pub. No. SAE-J885-APR80).

Warrendale, Pa.: 1980.

Swearingen, John J. Tolerances of the Human Face to Crash Impact (FAA

Pub. No. AM-65-20). Oklahoma City: Federal Aviation Agency Office of

Aviation Medicine, 1963.

Thomas, C., et al. “Crashworthiness Rating System and Accident Data

Convergences and Divergences.” Advances in Belt Restraint Systems:

Design, Performance and Usage (SAE Paper No. 840200). Warrendale, Pa.:

SAE, 1984.

Page 74 GAO/PEMD-95-5 Department of Transportation Crash Tests
Bibliography

U.S. Department of Transportation. Appendix AO (A-Optional): Part 572E

Dummy Performance Calibration Test Procedure. Washington, D.C.: NHTSA,

1993.

U.S. DOT. A Collection of Recent Analyses of Vehicle Weight and Safety

(DOT-HS-807-677). Washington, D.C.: NHTSA, 1991.

U.S. DOT. Correlation of NCAP Performance With Fatality Risk in Actual

Head-On Collisions (DOT-HS-808-061). Washington, D.C.: NHTSA, 1994.

U.S. DOT. Federal Motor Vehicle Safety Standards and Regulations

(DOT-HS-805-674). Washington, D.C.: NHTSA, 1989.

U.S. DOT. Head and Neck Injury Criteria: A Consensus Workshop

(DOT-HS-806-434). Washington, D.C.: NHTSA, 1983.

U.S. DOT. Laboratory Indicant Test Procedure: New Car Assessment

Program. Washington, D.C.: NHTSA, 1990.

U.S. DOT. Laboratory Test Procedure for: FMVSS 208, Occupant Crash

Protection; FMVSS 212, Windshield Mounting; FMVSS 219, Windshield Zone

Intrusion; and FMVSS 301, Fuel System Integrity. Washington, D.C.: NHTSA,

1993.

U.S. DOT. New Car Assessment Program: Plan for Responding to the Fiscal

Year 1992 Congressional Directives. Washington, D.C.: NHTSA, 1992.

U.S. DOT. New Car Assessment Program: Response to the NCAP Fiscal Year

1992 Congressional Requirements—Report to Congress. Washington, D.C.:

NHTSA, 1993.

U.S. DOT. The New Car Assessment Program—Status and Effect.

Washington, D.C.: NHTSA, 1982.

U.S. DOT. 1991 Traffic Fatalities Preliminary Report. Washington, D.C.:

NHTSA, 1992.

U.S. DOT, National Transportation Safety Board. Safety Effectiveness

Evaluation of the National Highway Traffic Safety Administration’s

Rule-Making Process. Vol. 11: Case History of Federal Motor Vehicle

Safety Standard 208: Occupant Crash Protection (NTSB-SEE-79-5).

Washington, D.C.: U.S. Government Printing Office, 1979.

Page 75 GAO/PEMD-95-5 Department of Transportation Crash Tests
Bibliography

Unterharnscheidt, F.J. “Translational Versus Rotational Acceleration—

Animal Experiments With Measured Input.” Proceedings of the Fifteenth

Stapp Car Crash Conference (SAE Paper No. 710880). Warrendale, Pa.: SAE,

1971. Pp. 767-70.

Versace, John. “A Review of the Severity Index.” Proceedings of the

Fifteenth Stapp Car Crash Conference (SAE Paper No. 710881).

Warrendale, Pa.: SAE, 1971. Pp. 771-96.

(973386) Page 76 GAO/PEMD-95-5 Department of Transportation Crash Tests
Ordering Information

The first copy of each GAO report and testimony is free.

Additional copies are $2 each. Orders should be sent to the

following address, accompanied by a check or money order

made out to the Superintendent of Documents, when

necessary. Orders for 100 or more copies to be mailed to a

single address are discounted 25 percent.

Orders by mail:

U.S. General Accounting Office

P.O. Box 6015

Gaithersburg, MD 20884-6015

or visit:

Room 1100

700 4th St. NW (corner of 4th and G Sts. NW)

U.S. General Accounting Office

Washington, DC

Orders may also be placed by calling (202) 512-6000 

or by using fax number (301) 258-4066, or TDD (301) 413-0006.

Each day, GAO issues a list of newly available reports and

testimony. To receive facsimile copies of the daily list or any

list from the past 30 days, please call (301) 258-4097 using a

touchtone phone. A recorded menu will provide information on

how to obtain these lists.

PRINTED ON RECYCLED PAPER
United States

General Accounting Office

Washington, D.C. 20548-0001

Official Business

Penalty for Private Use $300

Address Correction Requested

Bulk Mail

Postage & Fees Paid

GAO

Permit No. G100
GAO/PEMD-95-5 Department of Transportation Crash Tests