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NBSIR 74-561

Analysis of Methodology for Measuring

National Highway Traffic Safety

Robert G. Hendrickson, Alexander R. Craw

Technical Analysis Division

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

September 1974

Final

QC

100

.U56

74-561

1974

Prepared for . Mathematical /Vnalysis Division

Office of Accident Investigation and Data Analysis

Research Institute, NHTSA

Department of Transportation

Washington, D. C. 20590

NBSIR 74-561

ANALYSIS OF METHODOLOGY FOR MEASURING

NATIONAL HIGHWAY TRAFFIC SAFETY

Robert G. Hendrickson, Alexander R. Craw

Technical Analysis Division

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

September 1974

Prepared for Mathematical Analysis Division

Office of Accident Investigation and Data Analysis

Research Institute, NHTSA

Department of Transportation

Washington, D. C. 20590

Final

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director
I
Summary

The objectives of this study were to investigate the current practices of NIITSA in their

measuring and reporting on the major variables depicting the national highway traffic safety

situation, and to recommend new or improved techniques for a better representation of the

national traffic picture.

Tlie current methods of measurement are found to be too restrictive in the scope of description used and as expressed by variables defined at a level too gross to be sensitive to NllTSA vehicle and traffic safety programs.

The following major recommendations are directed to the improvement of measuring traffic

safety characteristics:

• Extend the current practice of depicting the National traffic safety situation from

fatalities to levels of inj ury- severity

.

• Adopt inj ury- severity per vehicle-year, inj ury- severity per driver-year, injury-severity per vehicle-mile and inj ury- severity per accident as preferred measures of traffic safety over fatalities per miles traveled, fatalities per vehicle-year and fatalities per driveryear.

• Adopt accidents per vehicle-year and inj ury- severity per accident as preferred measures of

traffic safety over fatalities per miles traveled .

• Adopt a level of descriptive capability (detailed in the report) to meet current and future requirements to characterize important factors in the National traffic safety

picture.

The following recommendations are directed toward improving program impact and sampling

techniques . ,

• Adopt geographical regions (described in the report) for data collection as a surrogate

for National statistics for purposes of projection and estimation.

• Use geographical regions for the location of Alcohol Safety Action Projects to enhance

effectiveness and evaluation.

• Improve current data processing techniques to accommodate more descriptors dealing with program impact and to provide facility in retrieving data for reporting and policy purposes.

The study emphasizes the need to standardize the estimation of vehicle-miles traveled and

to measure the impact of NHTSA programs by using composite indicators based on registeredvehicles, registered-drivers, vehicle safety systems and miles -traveled. Not only do these

variables represent the primary factors of the vehicle-driver-highway mix, but when expanded

into important subclassifications they provide a full spectrum of descriptors for analysis,

evaluation and reporting.

The complexity of evaluating programs and performing analyses of accident phenomena

virtually eliminates the current practice of depicting traffic safety by the use of rates and

requires a dimensional structure incorporating as many variables as can be quantified and for- mulated as indicators for purposes of policy, reporting and evaluation.

i
Talkie of ('ontcnts

Page

Suminan' i

i .1) Introduction 1

2.0 Background and CVerview 2

3.0 Objectives and Scope 3

3.1 Objectives 3 3.2 Scope 3

4.0 Review and Critique of Current Measurement Techniques 4

4.1 IntrcK.1uction 4

.1.1 - Coals iWSA 4 .l.z MAD Support Function 5

4.2 Limitations of Statistical Compilations 5

4.2.1 Annua 1 Report 5 4.2.2 Measuring Traffic Safety 6 4.2.3 Fatalities Vis-a-Vis Injury Severity. ^

4.3 Evaluation Summary y . . 7

4.3.1 Scope of Present Indicators 7 4.3.2 Limitations 7 4.3.3 Economic Ixjss as a Measure 8 4.3.4 Future Requirements '. . 9

5.0 Analysis on Proposed Improvements to Curiv..t Methodology 10

5.1 Introduction 10

5.1.1 Scope of Proposed Improvements 10

5.2 Safety Measures 10

5.2.1 Difficulties. 10 5.2.2 Candidate Measures 11

5.3 Statistics Based on Regional Data 17

5.5.1 Regional Data Base 17 5.3.2 Evaluation of State-Level Dc; , Rates 20 5.3.3 Review of ASAP Effort 21

5.4 -l^-tor Requirements 21

5.4.1 Objective 21 5.4.2 Variable Selection 21 5.4.3 Categories 21 5.4.4 Levels of Description 21 5.4.5 Evaluation of Levels of Description 27

5.5 Program Related Descriptors 29

ii
(1.0 ReconuiiLMida t ions

AjipcnJix 32

List of Tables

1 State oi' Michigan Accident IVdta, 1964-72 12

2 Index Representation, State of Michigan 1-^

7, Accident and Movement Data, State of Michigan l'.)h4-72 1 4 Injury-Severity Level per Accident, 1964-72 14

5 Exposure Indexes, 1964-72 14

6 Accidents per Vehicle Year, State of Michigan, 1964-72 15

7 Ten State Ranking, by Traffic Deaths; 1965-/1 19

8 Correlation .Analysis of State Groupings , 1971 19

l-'igures

1 Injury-Severity Indexes (State of Michigan, 1964^72) If, 2 Regressions on National and Ten State Traffic Deaths 18

3 Regression on National and Ten State Death Rates 18

iii

1.1) INTROnUCnON

This repoi't is subinittt\l iiiidci' ;i study agreement between rlic Mitheiiial ica I Aiials-sis Hivision,

\lirs\ and tlie Teclinical /\nal>'sis HivLsion, NBS. The report covers tlie i nvest i.nat ion of indicators

ol the National highway traffic safety situation with the intention of developing iiiiproveiiient s in the current methodology used for measuring and reporting featui'es of tral'fic safety as defined

licrc in.

Section 2 covers tlie general backgi'ound and situation leading to the researvh, and Sect i cm

-states tiie objectives and scope of tiic study.

Section 4 contains the review of current practice in developing imlicatoi's and desc ri ptnr>

,

and evaliutes the effectiveness of these practices in depicting the National situation, i iiiutations and gaps in the coverage of these indicators are ascertained, and serve, in part, as t ht- suliject of Sect ion S.

Section S deals with the analysis of the problem of measurement, addressing the 1 mutations

and gaps in jiresent metliods, and, in more general tenns, the necessary and desirable sti'uctiu'es for measurements to meet the tlemands of the NflTSA vehicle and traffic safety priority programs.

Section d contains recoiiDiiendat ions for improving current practice and meeting future re(|uire ments for measiiring and reporting National highway traffic safety features.

1
2.0 bai:ki;roiini) and (ivi;uvii:w

1 . 1 B;ick,moLiikl

The i;rowLnt; L'oiiip 1 e\ i ty of today's highway traflic activity lias iilacctl an iiicreas in.;; responsibility on the National Highway Traffic Safety Aibiiinistrat ion. This rcsjionsibi 1 ity takes the fonu of measuring and repor'ting on the general char'actcr of the driver-veliiclehighwa>' mix, and pursuing iirograiiis for effective counteriiieasures and standards on pre crash

accident avoidance, CT'ash injury prevention, and post-crash injury-severity reduction.

The Aibiiinistration (NIITSA) addresses the gamut of highway-traffic problems through the Motor Vehicle Programs, which concerns standards enforcement, operating systems, crash

worthiness, standards for vehic les- in-use, and defects investigation; the Traffic Safety

Program, which concerns standards development and implementation, state and community pro- grams, and alcohol count ermeasurcs ; and Planning and Programming, which concerns pi'ogram

planning, program evaluation and systems analysis. The Research Institute functions as an investigative unit on the aspects of the vehicle-driver system, and conducts programs con- cerning experimental safety vehicles, the safety systems laboratory, accident investigation

and data analysis, driver perfomiance research, vehicle structures research, and operating

svstems research.

'Iliese activities are enumerated to emphasize the diversity and range of the effort by

.Mlli'SA on accident avoidance and injury reduction, and to point out the critical need for appropriate data collection, measurements, evaluation and reporting in order to provide a basis for judging program impact and priority planning. They serve, also, as a functional

representation of the major variables in the National highway-traffic picture.

The functions of data collection, measurement, evaluation and reporting lead to requirements, on two separate, but related, levels. On the one level is the description, both

qualitatively and quantitatively, of those details dealing with the variables and parameters

of occupant safety and vehicle design in a crash scenario. The other level is the description, again qualitatively and quant itatively, of those aspects of highway-traffic activity

v\fhich describe traffic-safety patterns as seen from the perspective of the Nation as a whole.

These two levels are not exclusive, but they do present a problem in that descriptions

at one level may not necessarily supplement the descriptions at the other.

This dichotomy suggests that the functions of data collection, measurement, evaluation

and reporting need to be organized in such a way that the contribution of information from

each function serves both levels in an optimal sense, and provides a process of data

development evolving from detailed accident analysis to the indicators of the National

situation.

In summary, then, the need for an adequate and efficient description of the National

situation and program impact upon a- complex of automobiles, drivers and highways of unparalleled

variation, has become an essential concern of NHTSA, and it is to part of this problem that this study is addressed.

2.2 Ovei'view

In this report we discourse on the fact that measuring safety is a difficult task and

becomes more difficult [or more ineffectual) as more factors are introduced in time. The

faults of several variables that are currently used as indicators will be shown. The use of

an economic cost or loss model as an indicator will be discouraged and in its place, indicators

that avoid the pitfalls of costing will be recommended. It will be pointed out that the present use of indicators by NHTSA is restricted to those relating to mortality. As such these

present at best an incomplete description of the status of safety on the Nation's highways,

and are inadequate to measure the effectiveness impact of individual priority programs in improving traffic safety. We will then make recommendations for other indicators that have

specifically designated characteristics which better illustrate the National picture and at the same time are sensitive enough to reflect some effects of the NHTSA programs. We will

also recommend the use of special regions to assist in the depiction of the National scene

and enhance the demonstration of impact of priority programs.

2
3.0 ob,)i;i:tivi;s and scoi'ii

3. 1 Object i ves

The pi inLijial olijective was to (.Icvoloj) measures which ailcquate 1 y portray tlie overall

\atioiial highwa\' traffic safety situation. Secondaiy objectives included an examination of exposure measures, selection of varialiles sensitive to changes ln'ouglit about by the Motor \elHcle Programs and the Traffic Safety i"'roj;rams, an investigation of associated data collection

and processing needs ap|iropriate to the dcsircii indexes, and tiie ilevelopnient of candidate

liescr iptors leading to graduated levels of rci^rescnting the important variables of the National situation.

The indexes ai^e intended for tiie assessment of relative trends in injury redirction, to

iireasure shifts in distributions of injury- severity classifications, and r'eflect the contribution of the occupant -crasii protection standard in ter-rrrs of lives saved or accidents r-educed.

3

.

1 Scope

I'he study focuses principally on the effectiveness of currxnit jrractices of NIITSA to

rrreasure and present the characteristics of highway tr-affic safety. The scope includes a critique

and analysis of these practices for the purpose of developing new or improved rrrethods for

iireasuring and reporting critical infoniration. The criticiue is based on an examination of current statistical compilations, data collection systems and files, the utility of basic death and injury data, and an evaluation of the effectiveness of the statistical compilations of the

National traffic picture. Tlie analysis is directed toward the development of more compr^ehensive measures of accidentphenonrena using a broader base of descriptors and accident

criteria.

The perspective of the critique and analysis is primarily that of the Ntrthemat ical .'\nal\'sis nivision, Office of Accident Investigation and Data /Analysis, in terms of its support function

to the NHTSA mission. However, the total, overall requirements for reporting, evaluation,

data collection and measurement were retained as a necessary and desirable context in which

specific recominendat ions are made pertaining to a graduated capability in these four areas.

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4.1) RIA'lliW mi) CRITlQllli OF QIRkliNT MliASURIWhNT TliCllNlQllliS

-I. 1 Introdiict ion

This section siuiunar izcs the general goals and perspectives of the MirrSA role in vehicle

and tralTic safety activities and serves as a background for the critique and evaluation of

current jiractices for measuring accident phenomena.

4.1.1 Nkijor t">oals of the Nlfl'SA

The major goals are understood to he the support and promulagat ion of programs, standards

and projects at the National, State and local levels by the NHTSA, to relieve traffic pressures, obtain safer travel over longer distances, reduce the number and severity of injui^ies, ami pursue standards, designs and procedures addressing accident avoidance. Tlie specific goal of

the NirrSA is to reduce the national death-rate to 3.7 per 100-million vehicle-miles by 1980.

In order to obtain this goal the NllTSA is pointing toward a 141 reduction in total deaths per

\e,ir as a net effect from its priority |irograms.

4.1.1.1 Priority Prograjiis

l"he priority programs are in three categories, Crash Survivability, Alcoholic Aliuse, and

1-Aperimental Safety Vehicle. Two additional areas, Motor Vehicle Safety and Highway Safety, in cooi-dination with the States, address hazards of defective cars, selective traffic law enforcement, the driver control problem, vehicle inspection jirograms, traffic engineering and highway

safety standards. Progress through research programs involves accident investigations, iden- tifying the important aspects of human factors, vehicle -handling, and highway design.

4.1.1.2 Crash Survivabil ity

This program is divided into two areas. Occupant Packaging and Vehicle Design. Occupant

Packaging is further divided into passive measures (automatic protection) and active measures

[driver or occupant action). ITie second lifesaving aspect of Crash Survivability lies in designing the vehicle to absorb and def'ect collision forces so that the passenger comi)artment

remains a safety haven.

4.1.1.3 Occupant Packaging - Passive Measures

Passive measures protect automatically in an emergency without volition or action on the

part of the occupant. Based on research, numerous standards have been issued which enhance

crash survival chances. They specify safety oerfoniiance criteria for such potentially

dangerous features as steering coluirais, windshields, instrument panels, seat anchorages, door

locks, and fuel tanks. About 53% of the cars on the road now contain the basic safety devices

which were established as standard during 1968-71. New cars are driven more miles than older

ones accounting for nearly 651 of total miles driven. 1/

4.1.1.4 Occupant Packaging - Active Measure.;

Lap and shoulder straps are part of tne active protection package. Although far more

people reject than use them, research and testing have demonstrated their feasibility and

effectiveness. In November 1970, NHTSA issued a time-table (1972-1975) for improved seat and

shoulder belts and a gradual progression to a completely passive system covering lock-out,

compartment protection, and protection for all seat positions against impact and roll -over crashes

.

4.1.1.5 Vehicle Design

This priority program covers a wide range of vehicle improvement features addressing

energy absorption or deflection. A few of the major developments are (IJ front-end, energy

absorbing devices, (2) bending beams and crushable sections to distribute forces over the side

V

These data are from Traffic Safety, '71: A Report on Activities Under the National Traffic

and Ntotor Vehicle Safety Act .

4
Ill the veliiclc, (3) energy absorbing sti'uctures in the trunk area to incr-ease the siistainahle

impact force without compartment tiamage, (4) selective modification of roof pillars, and (S) simulations of occu]iant kinematics and motions during a crash scenario which are used as a starting point in designing energy - managing structures.

I. 1 . 1 .(1 Alcohol ic Abuse

The Alcohol Safety Countermeasures i''rogr;uii (A„SCP) is national in scope and effort. Its

]M"iiiiary goal is to identify the heavy-tir inking drivers and jirevcnt them from operating vehicles

while intoxicated. Its |irincipal operation is to channel as many of these drivers as possible

into treatment and rehabilitative programs. The total program embraces fl) financial assistance

for increasetl eiinihasis on the alcohol aspects of the State Iiighway safety prograjiis, (2J a national campaign of public education, {?>) research to produce new or imi:)rovcd methods and devices to reduce the problem, (4) training jiersonnel to carry out the various technical tasks connected with the program, and (5) federal funding of Alcohol Safety Action Projects (ASAP) to demonstrate the feasibility of concentrated effort on selected facets of the program.

4.1.1.7 lixperimental Safety Veliicles (liSV)

In the past design changes incorporating safety features were made on a gradual and piecemeal basis. Now, for the first time, whole vehicles are being designed, fabricated, and tested with safetv primarily in mind, 'fhe ESV program is achieving or contributing to the

following: (1) demonstrating the feasibility of advanced automotive safety performance features

through the design, fabrication, and testing of experimental vehicles, (2) stimulating public

iwareness of tlie safety and economic advantages of advanced designs, (3) encouraging the automobile industry to increase efforts in automotive safety design and to accelerate the in- troduction of advanced safety features, (4) applying the total systems approach of the program

to the development of new and improved Federal Motor Vehicle Safety Standards fr-'MVSS), (S) pennitting the introduction of safety features into production at the least possible cost through advance planning, (.6) opening the possibility of International Nfotor Vehicle Safety

Standards being developed with U.S. participation, and (7) making possible the free exchange

of safety technology among automobile firms for the first time in history.

4.1.2 MXD Support Funct ion

The Mathematical Analysis Division is responsible, in part, for developing data used in statistical compilations, accident files, ad hoc studies, reports and program impact.

Tliese activities support the mission of the Office of Accident Investigation and Data

-Analysis and the general requirements of NHTSA to measure the impact of their priority programs

and depict, with adequate precision, the major parameters of the National highway traffic

safety picture.

In reporting on the National safety situation, the current practice is to present a statistical compilation of the accidents and injuries occurring in the preceding calendai" vear, which is typified by the data given in Appendix A of Traffic Safety '72 : A Report on Activities

Under the Highway Safety Act . Tliis Appendix consists of a collection of 25 figures and 15 tables, which are intended to characterize the essential trends in highway-traffic safet\-.

4.2 Limitations of Statistical Compilations

4.2.1 Annua 1 Report

Tlie information contained in the Appendix of the annual report focuses principal !> on the

use of death statistics to present the national situation to the almost total exclusion of other important descriptors, e.g., injury-severity levels and accident -exposure criteria. An indication of this proclivity has been developed and reported in the appendix to this stud\'. It was obtained by grouping the data into convenient categories and observing the desci'iption

it provides. Selecting crash and damage (CD), vehicles (V), driver (D) and environment (I.) as the working categories, the counts are as follows:

CD -- 18 figures and 5 tables

V -- 9 figures and 6 tables

D 8 figures and 5 tables

E -- 3 figures.

5
IVithoiir (.'xccpt inn crasli and damage deals exclusively with death rates and counts; the

\eliicle catetjory presents data on registrations, nriles traveled and tr'avel -speed; the driver

data addresses only age, sex and rate of driver ]5opulation growth and envi ronment deals only

i^ith \ehicle travel on interstate, primary and secondary road systems. The constituents of

these categories ar'e given in detail in the Ajipendix. Included also arc the footnotes to these

figures and tables. They are interesting in the sense that they often provide a better statement or summary of what is occurring in the National situation than the figure or table to which the\' are attached.

4.2.2 Measuring Tr'affic Safety

Both the absence of a good working definition of highway safety and the complexity of

describing accident phenomena are major difficulties in develo]")ing safety indicators. The range

of interacting factors is so large that no single indicator is comprehensive enough to measure

and depict all the features of traffic safety of interest to NHTSA.

The three principal variables, registered-vehicles, registered -drivers and miles-traveled

iiave both good and bad features as indicators.

The good features are as follows: registered-vehicles can be expanded into the important

subclassifications which cover the vehicle population by type and by safety system; registereddrivers can be expanded into subclassif ications which cover driver characteristics and actions;

miles-traveled, although it can only be subclassifed into highway systems, is a dynamic measure

of the movement of the vehicle population.

Tlie bad features are as follows: registered-vehicles, although accurately measured through

registrations, is a static variable, and ther.'^ is no sure way of knowing the contribution of

vehicle-types to miles-traveled ; registered-dri/ers , although accurately measured by registration

is also a static variable and there is no .sure way of knowing the contribution of driver behavior

to accident causation; miles-traveled are based on various estimating schemes of very poor

accuracy and its subclassifications are not directly related to the NHTSA safety programs.

Lastly, none of the above address in an explicit way the three major causes of accidents: inattention, speeding and alcohol abuse.

However, when the three variables are combined they cover most of the factors in safety

analysis and an advantage is obtained which is not achieved otherwise. The disadvantage of a composite indicator, hoA\fever, still remains, as it does for all indicators, in that the dynamic

interaction of factors leading to an accident or increased exposure to an accident are not captured in a predictive model of accident phenomena. An example of this is given in the note to Figure A- 12, Traffic Safety 72: "Weekend crashes [4pm Friday-3am Monday) produce many more

fatalities in the evening and early morning hours than do weekday crashes. This is primarily

a result of increasee recreational driving on weekend nights and associated use of alcohol."

This situation clearly depicts the problem as to how to effectively develop these factors into

a useful indicator which characterizes and measures these dynamic interactions. The example shows

that driver behavior and habits arq interacting with a particular vehicle type under conditions

of weekend travel. A model of this situation would only be useful if it could predict the

reduction in accidents based on changes in driver behavior, vehicle-safety and the distance

traveled. Short of having such a model we seek indicators which will serve to measure these

conditions and reflect changes in trends as standards and programs bear on safety patterns.

4.2.3 Fatalities Vis-a-Vis Injury Severity

The statistical compilations in the annual reports-'' present fatalities or fatality-rates

by a variety of variables: vehicle miles, registered drivers, licenses in force, population,

and State. These basic variables are presented by both tabular and geographical displays, and

in many cases materially enhanced by notes attached to the tables or figures. At best, this

is depicting only a part of what is happening with regard to safety aspects on the highway system

Nationally. For example, in Appendix A of Traffic Safety '72, information is given on vehicle

travel on Interstate Highway Systems, Primary Highway Systems and Secondary Highway Systems,

- Safety '71 and Traffic Safety '72, Vol. 2.

6
bv both Lirhaii and rural classifications, yet tiicrc is no reporting of fatalities iiicutred on

the separate and respective highway systems. Reporting fatalities by highway system would lead

to a lietter "picture" of the safety aspects of the National system.

Other aspects of highway traffic safety are those relating to injury and property damage.

In addition to fatalities and injuries, damage to jiroperty is important because of its economic

impact. For example, Oiierations Researcli Inc. (ORl ) in their study!', have suggested mortality,

injury and property damage (M, M, PDl as the primary variables of an accident. There appears

to be no difficulty in accessing numbers of fatalities and extent of property damage, however,

there is a question on how to represent levels of injury severity. The reprcsentat ion chosen

may be helpful in some contexts and useless in others. In a second study (Wisconsin)fy ORI used Fatality, a- Injury, h- Injury c-Injury, and Property DamageV There is some possible

source of error because the assessment is made visually bya medically lay person, lixaminat ions

by the Office of Systems Analysis of NllTSA of the a, b, c code indicate no consistency of measurement. The sources of error lie in the definitions of the levels of severity, a misunderstanding

by the recorder of the data, or a misjudgment in the appearance of the severity of the injury.

For the specific purpose of detennining 'societal costs'!/due to motor vehicle accidents,

the Office of Systems Analysis suggests that in addition to a severity measure based on the nature of the injury, some notion of the permanence of the injury is needed. They have used

a breakdown of injuries into three severity groupings:

• permanent total disbility,

• permanent partial disability and permanent disfigurement,

• no permanent disability.

Although the a, b, c code is not sufficient for all program areas within NUTSA and recording

data in this system may vary in accuracy, it does serve an essential purpose of providing a practical recording scheme. Its shortcomings could be eliminated to a large degree through a coordinated effort by Federal and State governments to improve severity definitions, compliance,

standardization, accuracy and implementation.

4.3 Evaluation Summaiy

4.5.1 Scope of Present Indicators

At present there is no single, explicit set of indicators for the National Highway Traffic

Safety "picture." Indicators which are only partially satisfactory are fatalities per 100-million

vehicle miles, fatalities per one hundred- thousand population, deaths per one-hundred thousand

registered vehicles [or licensed drivers).

4.3.2 Limitations

The current practice of limiting the reporting of annual statistics of the National highway

traffic safety situation to fatalities gives an incomplete picture of the National traffic

safety situation.

A more complete picture can be obtained by reporting information on the number of injuries

incurred, their severity, and information on motor-vehicle related physical damage. The present manner of reporting fatalities, by a variety of tabular, graphical and word summarizations , is inadequate and should be extended to cover the reporting of injuries and their severities as well.

— Operations Research, Inc.: Development of a Cost Effectiveness System for Evaluating Accident Countermeasures , Dec. 1968, PB 183-440.

2/ — Operations Research Inc.: Development of Highway Safety Statistical Indicators, March 1971. DOT HS- 800-472.

3/— Lower-case letters are used to designate levels of injury-severity throughout this report.

-^Societal Costs of Motor Vehicle Accidents, Perliminary Report, April, 1972, NHTSA, DOT

7
With this additional reporting, NIFI'SA would be in a iiosition to obtain a gross evalu.ation

of shifts in the national liighway traffic safety situation over time, say, for example, from more

ro less serious tyiies of accidents. Hopefully, this could he associated as an impact of the

total ity of the NfffSA programs. One should not expect to be able to detect impact of imlividual

pVogrTims from this gross level of reporting. To accomplish this will require much more elaborate

(detailed) reporting or specialized studies.

A more elaborate scale for the classifications of injury severity (CRTS) is in use by the interdisciplinary accident investigation teams. However, this scale docs not ap])eai to be useful for easy classification of injury severity by non-specialists.

We again note that one of the listed main goals of NHTSA is to reduce the number and severity

of injuries. Thus there is a requirement that the number of injuries as well as some representation of the severity of injuries be included as indicators of progress toward this major goal.

.'\nother listed goal of NHTSA is to obtain safer travel over farther distances. This call s again for a more reliable determination of vehicle miles and for other indications of "safer

travel ." One indication of "safer travel" might be a shifting from serious to less severe accidents

in each severity category.

In particular, there are several measures which do not appear to contribute to the characterization of the traffic -safety picture.

Traffic deaths per 100,000 population attempts to relate two totally different variables

and does not connote the same relationship as in measuring natural deaths by population size.

In the latter, deaths from all causes are distributed over the total population, but traffic

deaths are only taken from the driving population, and then only from a subset of those who are

in motion.

To compare deaths from automobile accidents with other causes of death is beside the point

and irrelevant to the general objectives of NHTSA. It further implies, somewhat subtly and

indirectly, that to get traffic deaths in line with other causes of death makes it more acceptable

and suggests progress toward its control. As long as alcohol abuse, speed and driver inattention

remain the principal contributors to accidents, all within control to a large degree, deaths

from traffic accidents should not be treated in the same way as other sources of deaths where occurrence and control have entirely different features.

The monthly mileage-death rate seems marginal in utility since it obviously reflects

seasonal trends. It has an ultimate value in time series analysis and in depicting some features

of the National situation, but it is not a critical measure, and is no better than the mileage

estimates on which it is based.

The measure, average free-moving travel speeds, is not currently used as an indicator of

anything in particular, except perhaps of a combination of vehicle design and posted-speed

factors, which does not imply either safety or hazard unless it is related to other elements in the vehicle -driver -roadway mix. However, the recent lowering of highway speed limits has pro- duced a marked influence on fatalities, which suggests that relating this measure to numbers of

deaths or accidents is a more meaningful use of this data than reporting travel speeds in absolute terms.

To summarize: the present emphasis of NHTSA indicators is on mortality relative to a set of psuedo-exposure measures that are either poorly determined (as in the case of vehicle-miles)

or non-relevant (as is total population) or not used (average free-moving travel speeds).

These indicators provide at best only a partial description of National traffic safety. In addition, the current indicators cannot be used to measure the effectiveness of any particular NHTSA priority program.

4.3.3 Economic Loss as a Measure

4.3.3.1 Introduction

A thorough and intensive examination of economic loss models and their use as a measure

of program effectiveness is beyond the scope of this report, but economic loss as used by NHTSA does require that some assessment be made of its application. The annual reports refer

8
ti), ;hu1 impl\' nieanint; from, economic cost-benefit analysis as an ultimate siuim i nj^-uj) of the

impact of hi;-;hway- traffic accident injuries and deaths upon society. Its simplicity, however,

does not imjih' profundity, and its mechanism does not iniiily integrity, for the evaluation of

economic and societal costs is very complex in structure and scoi)e.

4.3.5.2 liva luat ion

Bconomic loss as a measui'c of program effectiveness or of the overall highway-traffic picture

was rejected on three basic jioints: (1) it is conceptually inadequate, (2) it introduces wide

variances into the problem of measurement, and (3) it docs not provide additional infonruition beyond that inherent in the data on which it works.

The evaluation of loss does not go much beyond a cost -account ing and earnings- lost concept,

and results in converting the physical and property damage associated with an accident into a dollar value. This value, however, does not necessarily represent an economic loss, and certainly

does not qualify as a measure of societal loss. In modelling the impact of accidents, the

individual and society must be viewed as receivers and investors, and accidents as unforeseen

instruments of financial redistribution.

The mechanics of converting the physical and property damage to a dollar-value introduces

the wide range of cost estimates as a variance in the dollar-value output of the model. Any

indexes based on this output cannot be used without knowing the character of its distribution, and

consequently reduces its usefulness.

Since the economic loss calculation is only a conversion of diverse consequences of an accident to a dollar-value, its function is limited to only a mathematical convenience which

fails to add to the information available in the inpu. data. The conversion actually obscures

rather than clarifies, for it maps many important details of accident causation and consequences

into a common but different coordinate.

As a consequence of these three basic issues, it was decided to forego any use of economic

loss models as measures, and assume that the objectives of the study can be obtained more effectively by dealing with the basic accident data directly.

4.3.4 Future Requirements

The description of the National highway traffic situation will become increasingly difficult

to obtain by using gross or aggregated indicators. The factors of safety now entail human

parameters, vehicle safety systems, sophisticated energy absorbing or distributing devices and elaborate traffic control; each of which is difficult to isolate and measure as a separate

component

.

The methodology for measuring and evaluating safety features will become more intiicate

than more simple, more detailed than more gross, and require more data on more descriptors;

this will require a greater investment of resources to equip NHTSA for its role and responsibility

to measure and report on highway safety.

9
S.O ANALYSIS OH l'R0r0Si:i) IMI'ROVIM'NTS TO ClIRllliNT MI :n 101)01 .OCY

5. 1 Intfodiict ion

This section relates the work and investigations on-.thosc aspects of current practice

where limitations and gaps exist, and where new or improved techniques arc needed for developing

descriptors for measuring National highway traffic safety. These investigations address exposure measures, statistical regions, and structures for descriptor identification for certain

levels of measurement and reporting requirements. Special attention is given to descriptors

possessing double utility as measures of the National situation and sensing changes brought

about by the vehicle and traffic safety priority programs on NllfSA.

5.1.1 Scope of Proposed Improvements

The proposed improvements to the current practice of measuring and reporting on highwaytraffic safety are presented in the following sections on safety measures , statistical regions

and graduated descriptor arrays .

The current practice of representing exposure by vehicle-miles--^ traveled or registered

vehicles can be improved by the addition of two new measures: accidents per vehicle-year and

injury-severity level per accident. These measures relate driver safety more closely to the

parameters of accident phenomena and to the performance of the vehicle in protecting occupants

after an accident has occurred. These rates shift the emphasis of measurement from fatalities

to injury-severity, and from crash damage to accident potential.

The concept of using statistical regions in the place of nationwide data collection is introduced to gain three principal advantages: (1) to obtain a surrogate data-base representing

the National situation, (2) to reduce the amount of data needed for projections and estimates,

and (3) to serve as locales for concentrated program intensity.

The surrogate data-base would provide a sampling source on the National situation, would

be more responsive to reporting requirements because of the smaller number of units, and would

provide more consistent and reliable data because of the size and concentration of the effort.

Three or four such regions could cover on the order of 50-60% of total fatalities. Data would

still be gathered from all 50 States, but policy and program decisions would be based on

regional data and activities. Programs, such as the alcohol abuse project (ASAP), would enjoy

a higher level of effectiveness if they were concentrated in such regions. An advantage is obtained from covering a larger area, and having more data on which to base evaluations.

In order to measure and report more effectively on the traffic picture, it is necessary to improve on current practices by developing a more sophisticated description of accident data. The approach taken to achieve this was to define sets of descriptors, each set possessing a level of capability to describe accident phenomena, and then to organize these sets from the

lowest required level to the highest desired level. This provides a progression of sophistication

and relates the level to the NHTSA requirements for measuring and reporting. Each set, or array, is evaluated on its capability, its implementation requirements and its time horizon.

Capability is judged on the basis of two criteria: depiction of the National situation, and

sensitivity to changes in that depiction brought about by NHTSA priority programs in vehicle

and traffic safety standards and design improvements.

5.2 Safety Measures

5.2.1 Difficulties

Although it is one of the basic variables in the depiction of accident phenomena, vehiclemiles traveled has not been completely satisfactory as a measure of safety.

The difficulties are in getting good estimates of miles traveled from the States, whose

methods vary (usually based on gasoline sales tax revenue, traffic counts or formula extrapolation!

and in the wide variety of highway, turnpike, road and street types, urban and rural. Further,

vehicle-miles traveled is not directly related to the three major causes of accidents: speed,

— Vechicle-miles traveled is retained in this discussion in the event NHTSA prefers it for reasons

of tradition and precedence.

10
alcohol and inattention. It is probably true that most miles traveled are done so salely;

it is more likely that the factors Leading to an accident are of a particular kind, ai'c not totally random, and occur with a greater probability in certain conditions than in

othei^s. On this basis, deaths per vehicle-miles traveled is not a good model for measuring

program goals or representing the critical features of traffic safety. Consequently, rates or trends based on the use of vehicle-miles traveled may be highly imprecise and not reflect

the inlierent factors of accident causation or potential. l-.x]50sure is difficult to quantify

because it is essentially a non-event; it is rather an expression for the probability that

a breakdown will occur in a driver-vehicle-roadway scenario which results in an accident.

ILxposure is constantly present, but it's materialization into an accident is dejiendent on many factors not reflected in the simplifying vehicle-milcs-traveled variable.

Even if these difficulties could be resolved, the value of using vehicle-miles-traveled

is likely to lessen in the future because as cars become safer, and more miles are traveled

by more people, the rates per vehicle-miles traveled will decrease. This may divert attention

from statistics on factors regarding deaths and injury- severity. Because of the type of motor

vehicle and traffic safety programs, the emphasis on measuring safety is likely to shift to evaluations of occupant protection and away from aggregated estimates using miles-traveled.

5.2.2 Candidate Measures

In the following analysis registered -vehicles is used as the basic variable in the

foi-mulation because it is accurately measurable and can be subclassif led into descriptors

which reflect the major objectives of NHTSA safety programs. The results of the analysis may be expressed in terms of vehicle-miles or registered -drivers just as well as by registered - vehicles . An evaluation of national safety using all three, further classified by road system,

would present a comprehensive over-view of the major factors in traffic safety analysis. The

accuracies of these three variables are not comparable however, but among them their combined

subclassifications would cover most of the primary and secondary attributes of interest. The

principal superiority which registered -vehicles has over the other two is an advantage of a qualitative nature, which is important to measuring program impact, and lies in the relationship the variable has with the NHTSA priority programs. Changes in vehicular safety design

brought about by NHTSA programs will alter the attributes of the automobile population for

which the number of registered-vehicles stands as a measure. This permits the use of reg- istered-vehicles in a dual role - to characterize traffic safety and to reflect changes in vehicle design. The former invoU^es counts and distributions, the latter involves descriptors

of vehicular attributes for refined presentations of characteristics of the automobile population. This latter advantage is unique among the candidates for measuring traffic safety.

.As alternatives to the current practice of representing traffic safety, four measures,

days-lost, injury -severity per vehicle-year, injury-severity per accident and injury severity

per registered-driver are developed in terms of their attributes and value as formulations of

traffic safety and measures of program impact.

5.2.2.1 nays Lost

We define days-lost as the number of productive days which are lost to society because

of injui-y or death. The loss includes days spent away from work under medical care, rehabilitation,

or disability, and in the case of death, an estimate of ex]3ected balance of days-of -labor not realized. The estimation of days-lost would be modelled in much the same way as economic loss with the important difference lying in the conversion of injury or death to days-lost instead

of a dollar value. It has the advantage of being sensitive to motor vehicle and traffic safety programs because it is directly dependent on the medical consequences of injuries sustained,

and may be expressed in terms of severity levels, if such an order of resolution is desired.

It has a serious disadvantage, however, similar to the cost variability noted in economic

loss models in that the number of days -lost could depend on many factors other than the type and degree of injury. This situation precludes the use of days-lost as a preferred

indicator despite the advantage cited above. It has been included, however, for completeness,

as a possible measure comparable to economic loss but less desirable than the injury -severity

per vehicle-year or injury -severity per accident.

11
S.2.2.J Injui y- Sever ity per Vehicle-Year

A second alternative is to measure safety as a function of injury-severity .anil vehicles.

Tliis fonmilation iirovides a measure based on the driver's exposure to accident, and tleals diiectly with factors not used in current ]iractice. Tt has the advantage of being foniiul.ited without using vehicle-miles traveled, but both derivations are given should NllTSA prefer one

to the other for reasons of precedence or content.

The following formulation, p>roposcd as a measure for traffic safety, is based u\x)r\ the following variables: (1) number of accidents. A, (2) the number of registered-vehicles, V, and (3) the number of injuries per accident by severity class "x" (where "x" stands for either

a, b, c), I^/A.

The driver is essentially concerned with his risk when he travels, so the first value to compute toward this total risk is accidents per vehicle per year which is A/V. His ex])osure to injury over, say one year, is then given by where "x" is an index of the set of severity

levels. We have expressed two concepts of exposure, one is the accidents per vehicle per year

and the other is iniurv-severitv. bv class, per vehicle per vear. The same equation can be derived

as follows: Introduce vehicle-miles-traveled, M, and average miles per vehicle per year, M . then

compute

and finally

V

A

= P (accidents per vehicle -year)

(injury- severity per vehicle-year)

(2)

(3)

Let us now see what this formulation provides in the way of insight and information,

which is not given by current measures, on the National situation and the impact of vehicle

and safety programs.

Table 1 gives basic data from the State of Michigan from 1964 through 1972, which we

shall use for the application of the above proposed measure of safety.

Table 1 - State of Michigan Accident ]lata, 1964-72

Year

1

' Killed f 1 nj ured

f Injured, By Severity

a b c

64 2120 .144,623 42,t83 35,979 65,961

65 2129 155,258 46,102 37,864 71,292

66 2296 156,694 48,133 38,446 70,115

67 2123 151,297 44,219 36,026 71,052

68 2388 160,413 48,968 38,507 72,938

69 2487 175,400 51,700 40,620 83,080

70 2177 161,719 45,426 37,193 79,100

71 21.S2 157,664 30,888 42,131 84,645

72 2258 178,929 28,663 49,010 101,256

12
Using 1964 as a base-year, wc construct indexes for Tabic 1, given in lahle 2.

Table 2 - Index Representation, State of Michigan

I C3 r

j # Injured, By Severity

" Ml ifcrU " 1 nj ured a b c

64 1.000 1.000 1 000 1.000 1 000

65 1.004 1.074 1 080 1.052 1 081

66 1.083 1.083 1 128 1.069 1 063

67 1.001 1.046 1 036 1.001 1 077

68 1.126 1.109 1 147 1.070 1 106

69 1.173 1.213 1 211 1.129 1 260

70 1.027 1.118 1 064 1.034 1 199

71 1.015 1.090 724 1.171 1 283

72 1 1.065 1.237 672 1.362 1 535

Table 3 provides additional data needed to develop the analysis.

Table 3 - Accident, Vehicle, and Movement Data, State of Michigan, 1964-72

'Average Miles Vehicle -Miles Number of Total No. Traveled per Traveled per Registered Accidents Year Vehicle per year, M Year, M Vehicles, V A

64 9,647 38.3 X 10^ 3970 X

10"^ 284,444

65 10,248 40.9 3991 310,598

66 10,910 43.9 4024 302,880

67 10,912 45.1 4133 299,004

68 11,142 48.1 4317 305,495

69 11,341 50.9 4488 331,223

70 11,644 53.2 4569 313,715

71 11,709 55.5 4740 314,015

72 11,740 58.1 4949

• 359,745

We now calculate equation (1) and give the results expressed as indexes in Tables

4 and 5.

13
Table 4 - Injury-Severity Level per Accident, 1964-72

Severity Level - a Severity I^evel - b Severity Level - per Accident per Accident per Accident

Year Value Index Value Index Value Index

64 .150 1.000 .126 1.000 .232 1.000

65 .148 .989 ,122 .964 .230 .990 66 .159 1.059 .127 1.004 .231 .998

67 .148 .989 .120 .953 .238 1.025

68 .160 1.068 .126 1.000 .239 1 . 030

69 .156 1.040 .123 .970 .251 1.082

70 .145 .965 .119 .937 .252 1.087

71 .098 .656 .134 1.061 .270 1.162

72 .080 .531 .136 1.077 .281 1.214

NOTE: Values have been rounded to three places from six.

Table 5 - Exposure Indexes, 1964-72

Year H

a H

c

64 1.000 1.000 1 000 1.000

65 1.010 .985 1 012 .942 66 .994 .943 937 .955

67 .890 .861 .926 .861

68 .932 .870 .899 .916 69 .944 .881 982 .915

70 ' ,807 .783 909 .778

71 .532 .862 .944 ,746

72 .480 .974 1 097 .761

14
In order to draw contrasts among these formulations it is of interest to examine the amoimt of information in equation (2), which measures safety as the number of accidents

per vehicle per year. This calculation is given in Table 6.

Table 6 - Accidents per Vehicle - Year, State of Michigan,

1964-72

Year A/M M -(f)

«

64 7 43 X 10 9,647 71.7 X 10"^

65 7 59 10,248 77.8

66 6 90 10,910 75.3

67 6 63 10,912 72.3

68 6 35 11.142 70.8

69 6 51 11,341 73.8

70 5 90 11,644 68.7

71 5 66 11,709 66.3

72 6 19 11,740 72.7

The driver's safety is now given as the number of accidents per thousand miles of travel

and we can see by Table 6 there has been little change since 1964.

So despite the decline in exposure as given by A/M the increase in M offsets this trend. This information is better than that provided by current practice, but not as useful or descriptive as that given by equation (3) where injury -severity is introduced.

In sum, this formulation of safety uses injury-severity, by class per vehicle -year , as an indicator for both the national situation and sensing changes brought about by the impact of

vehicle and traffic safety programs. The data of Table 5 are plotted in Figure 1. The lines

follow a closely grouped downward trend until 1970 when something of a major impact occurred.

After 1970, fatalities remained steady but the spread in injury- severity diverged by large

amounts. It follows, for whatever the causes of the change in our example data, that the exposure to injury or death is better portrayed when separated into its components. This

separation provides information on the relative frequencies and trends of injury severity, and

the shifts in these distributions. This concept can be enlarged to include more descriptors

of driver, vehicles and highway variables, making the method applicable for program impact as well as depicting the National situation. As Figure 1 shows, an indicator based on % alone

would give only a partial account of the situation.

5.2.2.3 Injury- Severity Per Accident

This measure was computed as a part of our analysis above and is given in. Table 4. These

values permit an evaluation of injury production on a per-accident basis. As such, they include

such factors as driving habits, driver conditions, vehicle safety design and occupant protection

systems. At this level of measure these factors are not separable, as they are not for the

injury-severity per vehicle-year measure,. They do permit the inclusion of the additional

dimension of accident -injury trends. These, with the other indexes of safety measured on the

basis of injury- severity related to movement, provide at least, when coupled with current practices, an improved characterization of the National situation with potential for extension to cover program parameters. ,

5.2.2.4 Injury- severity per Registered- Driver [per year)

As a measure injury- severity per registered-driver year serves as an extension of the

other measures by virtue of the additional descriptors which can be made by subclassification

of driver attributes. Since the major causes of accidents are more closely related to driver

15
64 66 68 70 IZ

FIGURE 1 INJURY SEVERITY INDEXES

(STATE OF MICHIGAN, 1964-72)

16
habits or behavior than to the registered-vehicles or vehicle-miles variables, this measure

is an important dimension in accident analysis.

In the analysis of Section 5.2.2.2, registered-drivers may be used instead of vehicles

and a similar index would result. However, the principal contribution of this measure to analysis is in its subclassifications and their contribution in depicting safety features. Figure A- 6, Traffic Safety '72, shows that the ratio, drivers/RV, has a linear, but declining

relationship. In 1950 the ratio was 1.25 and in 1971 it was unity. This means that for some kinds of analyses we need only deal with registered-vehicles . But as a principal coordinate

in the vehicle -driver-highway mix and the sophisticated safety programs dealing with vehicle

safety systems and driver-alcohol and driver-training programs, the registered-driver should

be studied at the same level of detail as other measures.

Post accident statistics are essential to the success of index measurements. The two aspects of this phase of accident analyses are the performance of the safety system under

the conditions of driver behavior and the extent of injury as a function of driver condition

and attributes. These factors interact in the sense of trade-offs between reasonable behavior

and reasonable levels of safety equipment to achieve designs and standards for safe driving. Because of these conditions NHTSA safety programs are likely to be evaluated in terms of

impact of design-behavior interactions. Consequently measures of driver attributes will

increase in importance.

5.2.2.5 Summary

Four measures of safety have been proposed to supplement and extend the current measures

of the National traffic picture. If these indicators are refined to include appropriate

subclassification of their attributes and supported by the requirements for data collection,

they possess the potential for measuring operational impacts of vehicle and traffic safety

programs, and provide a basis for depicting national trends. They may be viewed as the

principal dimensions for developing different facets of the total picture of traffic safety.

In the driver-vehicle-highway mix the subclassifications of registered -drivers , registeredvehicles and highway systems combine to cover the major indicators of program impact and

analysis of trends.

5.3 Statistics Based on Regional Data

5.3.1 Regional Data Base

Since a few States experience a large number of accidents the premise that a sub-set of

the forty- eight Continental states could provide data for indicators was studied with very

interesting results.

For the period 1965-71 (7 years) the ten States highest in deaths were ranked for each

year. These sets, one for each year, had a very stable membership with virtually no significant change over the seven-year period. There were a few displacements of position (but never more than a switching) , and only in the second year was there any bumping from the list (and

this occurred at the bottom) . Table 7 presents these sets by year and rank.

17
NMV

45

40

35 - 45

ZO^ 40

20

NMV^-1. 027+1. 627 D

NT=2.321+1.96 D js

2 5 30 35 40

TEN-STATE TRAFFIC DEATHS, D

FIGURE 2 REGRESSIONS ON NATIONAL &

TEN STATE TRAFFIC DEATHS

4.5 5.0 5.5 6.0

TEN-STATE AVG. DEATH RATE,'Djs

FIGURE 3 REGRESSION ON NATIONAL &

TEN STATE TRAFFIC DEATH RATES
Table 7 - Ten State Ranking, by Traffic Deaths; 1965-71

Rank 1965 1966 1967 1968 1969 1970 1971

.

1 California California California California California California California

Z Texas Texas Texas Texas Texas Texas Texas

3 New York New York New York New York New York New York New York

4 Ohio Ohio Ohio Ohio Ohio Ohio Illinois

5 Illinois Illinois Illinois Illinois Illinois Illinois Ohio

6 Michigan Michigan Perm. Perm. Michigan Perm. Florida

7 Perm. Perm. Michigan Michigan Perm. Michigan Perm.

8 Florida Florida Florida Florida Florida Florida Michigan

9 N. Carolina N. Carolina N. Carolina N. Carolina N. Carolina Georgia N. Carolina

10 Indiana Georgia Georgia Georgia Georgia N. Carolina Georgia

In order for the ten- State data to serve as a surrogate it must be shown to be representative

of the National data. The analyses supporting the suggestion are given in Table 8 and Figures 2 and 3.

Table 8 shows a comparison of the product -moment correlations of deaths (D) with deaths per 100-million vehicle units (D/10%) , deaths with registered vehicles (RV) , and deaths per 100- million vehicle miles with deaths per ten-thousand registered vehicles (D/IO^V) , for the ten- State and National data.

Table 8 : Correlation Analysis of State Groupings , 1971

Variables Ten-State National

D . D/IO^I -.38 -.10 D ~ RV .91 .97 D/108m ~ D/IOV .95 .89

Figures 2 and 3 provide additional graphical information on the relationship between the ten-State data and the National data. The data are plotted as coordinate pairs for each year

of the period taken in the analysis.

In Figure 2 are the linear regressions of the ten-State total deaths (Rps^ versus the National motor -vehicle -deaths- only (NMV) and the National total traffic deaths (NT). The coefficient of

correlation between NT and Dpg is .96 over the seven year period of the data.

Figure 3 shows the regression for the ten-State death-rate average with the National death

rate (deaths per 100 million vehicle miles) over the period '65- '72. The correlation is .99 with

a standard error (s.e.) of .04175.

These results suggest the following relationships. Table 8 shows that the two death-rates

are strongly correlated but that deaths correlates strongly with registered-vehicles. Since the

ten- State data is embedded in the National data the influence of the balance of the States is clearly defined. For the first pair of variables they have a neutralizing effect, for the second a supportive effect and a slight degrading effect on the third. Figure 2 shows the strong linear

relationship between the ten-State numbers of deaths and the National numbers of deaths by NMV' and NT. The fit with NMV is particular good, which is advantageous to measuring traffic safety

19
since the deaths and injuries associated with motor-vehicles-only are precisely those at which

tiie NHTSA programs are primarily aimed. Figure 3 shows the remarkably good fit between the

National death-rate and the average death-rate of the ten-State data. Ihe regression is exceedingly tight with a very small standard error and the slope is very close to unity. Also, the correction term in the regression is quite small.

These relationships suggest the following conclusions. First, death rates tend to he weakly

ajid negatively correlated with numbers of deaths. This implies that death rates are a poor measure

of traffic safety at either the state or National level and high numbers of deaths do not nec- essarily imply high death rates. The importance of this information is that low death rates may mask safety problems which should receive attention. Second, the ten-State data represents the

National situation in death-rates, in motor-vehicle -only deaths and between numbers of deaths and

registered- vehicles. Third, the death-rates of the ten-States are distributed in the National

death-rate data in such a way as to have a lesser range than the National data but have a close

approximation to the average of the national death-rate distribution. The weak negative correlation

of deaths with death-rate in Table 8, suggests that the ten-State death rates tend to be slightly

lower than the death-rates associated with the balance of the States in the National data. It appears that death rates in general are not by themselves reliable measures because they fail to correlate significantly with numbers of deaths.

These results indicate that the ten-State set may be considered as a potential source for projections and estimates of National trends.

Unfortunately, these ten States (Table 7) do not divide well into regions. California stands

alone; New York and Pennsylvania are contiguous; Ohio, Michigan and Illinois group well, and

Georgia and Florida also make a region. But Texas and North Carolina are isolated, as is California,

making it difficult to identify naturally occurring regions which experience a high rate of accidents. North Carolina could be dropped without hurting the statistics since it ranked no higher

than ninth (reference Table 7), but Texas, ranking second throughout, should be retained. This

would provide five regions: I - California, 11 - Texas, III - New York and Pennsylvania, IV - Ohio, Michigan and Illinois, and V - Georgia and Florida. All of these States, except Ohio and Pennsylvania, now report injury- severity data in the a, b, c code. If contracts or arrangements

could be made with these two States to respond also with a, b, c code, this nine-State data set may have the potential as a data surrogate. A follow-on Phase II of this study, if approved,

would examine the potential of this concept and identify its capability to fulfill what appears to be its promise.

Another possible advantage of the regional approach to data collection would be to establish

ASAP'sVin these regions on a widespread basis. This might improve the sampling base for the

evaluation of the program with other vehicle and traffic safety programs in the region. It probably

would permit a greater effectiveness of the ASAP since it would now apply to the region rather than

to a city or county, and would gain higher visibility with the public.

5.3.2 Evaluation of State-Level Death Rates

In 1971 Nevada had a death rate of 7.3 per 100-million vehicle miles traveled, while California

had only 3.9. However, the actual number of deaths in Nevada was 275, while California had 4,777

deaTihs, a factor of 18 times as great. Tliis suggests that variables other than vehicle-miles

traveled should be used to quantify the accident -situation at the State level. Note also the

negative or weak correlations given in Table 8 between traffic deaths and traffic death rates.

If priorities of funding, resource allocation, or programs were based on mileage death rates only,

then, as suggested by the California and Nevada data, inappropriate decisions might result.

Since accidents arise from a complex of factors, often masked by measures based on aggregation,

the most effective measures are those which use the essential descriptors of a given situation,

are based on an examination of causes of perceived differences between similar conditions, and

include a determination of differences derived from the circumstances and specifics contributing

to accident phenomena. Rate measurements at the State level are more sensitive to variations in data than identical measurements at the National level, so the integrity of the measurement is correspondingly more critical if it is to be of any use at either level

.

- Alcohol Safety Action Projects.

20
Rcx'iew ol" .\S!\r liffort

As a result of studying the operations and functions of the ASAI' ptoj^tain ' Iheic .ipix-ared to he two aspects of measuring program effectiveness which miglit he liel[)eil hy locating ASAI' centers within the aforementioned statistical regions. Although the evaluation of program

tiveness examined the residual component in the time-series data, it ajipears that wlien the niimh(M of fatalities is small in each of the few ASAI' grou|is the residual component does not survive

the significance tests. ITie inherent random error of several, or many isolated and diveisehlocated, data sources is going to be greater than the random error associated with closelv g.r-oupcd data sources, integrated and coordinated within a specified region.

The second aspect of obtaining and measuring effectiveness deals with combining data fi-oin isolated and diversely located ASAPs as opposed to data derived on a regional basis. In the former the county and city conditions are likely to vary considerably from location to location,

but in the latter, whatever conditions do prevail are consistent for all ASAPs located in the region. This results in the data being more consistent with respect to externalities and more

free from the influence of aggregated random error.

5.4 Descriptor Requirements

.S.4.1 Olijective

In order to develop a scheme or structure for obtaining indicators having the jnoperT ies we desire, and have stated above it is necessary that the variables selected possess these pro]XMties.

In addition, these variables should be capable of extended definition into sub-classes, ami be measurable and reportable within the context of current practice for data collection.

5.4.2 Variable Selection

Tlie highway- traffic safety activities are organized by categories which are defined by classes of information. The classes may be further divided into subclasses according to the level of

complexity and detail desired. The classes and sub-classes become the variables, or descr iptc^rs

,

of the structure; the structure determines the level of detail.

5.4.3 Categories

The highway traffic accident situation is characterized by five major areas: (1) driver,

(2) vehicle, (3) envirorunent , (4) accident factors, and (5) injury -severity (includes fatalities).

The coverage of each category is determined by the number and type of classes it contains, similarly with subclasses per class. A structure is determined, then, by the quantity and quality of

subclasses or classes in the amount of descriptive detail they provide.

5.4.4 Levels of Description

A level is defined as a particular set of descriptors, organized by category, class and sub- class, which provides a capability of characterizing accident phenomena. The levels discussed

below are focussed principally on the major variables of the driver-vehicle-roadway system.

The omission of descriptors for pedestrian accidents and non-vehicle accidents is acknowledged

[Levels 3 and 4, do, however, include pedestrians]. It is assumed that the currently developed

statistics on these, and other secondary features, will be continued as they are, and that any

improvement contained in the following levels of descriptive capability that apply to these areas

of accidents will be developed and used accordingly.

A first level of description should be no less than that provided by current practice and

should be considered a necessary and basic structure upon which more complex structures may be

developed. Several levels are constructed below whicli fonn a graduated capability for depicting

the national traffic safety picture.

- DOT/NHTSA, "Alcohol Safety Action Projects," 1973 .Annual Report, Vol. 1, Summary.

21
Level 1 Descriptor Array

Category Class j Subclass

Driver Age

Sex Male

Female

Vehicle Body type Regular

Compact

Environment Urban Roadway

Rural Roadway

I -System

I -System

Accident Factors Manner of Collision

Speed

Property Damage

# of Occupants

Head-on

Side

Rear-end

Injury Severity # of Deaths

# Injured

# Non- injured

Level 1 provides a necessary minimum of information, and extends current practice only by

its inclusion of the number of injured and non-injured in the injury- severity category. This

extension, and level 1 in general, does not begin to approach the degree of response desired

for program impact or depicting the National traffic picture.

Level 2 provides a considerable advance over Level 1. The Injury- Severity category has

been enlarged to include the coded severity levels, the Accident Factors category is more de- tailed and the Environment category has been augmented by additional detail. Level 2 is not yet sufficient, however, in terms of descriptors which would be sensitive to vehicle and safety

programs. For this purpose the Vehicle and Accident Factors categories need additional classes

and subclasses. These additions are the basis for the Level 3 capability.

22
Level 2 Descriptor Array

Category Class Subclass

Driver Age

i Sex

Training

Over 60 25-59 Under 25

Male

Female

None

High School

Commercial

Vehicle Body Type

Year

Compact

Regular

Camper

Small Car

Environment Urban Roadway

Rural Roadway

I -System

Freeways

I -System

Turnpikes

Weekday

Weekend

Daylight A.M. Daylight P.M. Night A.M. Night P.M. J

23
Level 2 Descriptor Array (Continued)

Category | Class Subclass

Accident Factors Manner of Collision Head-on

Side

Rear-end

Overturned

Struck fixedobj ect

Speed Above posted

limit

.

At posted limit.

Under Posted

limit.

Injury Severity

Property Damage

Number of Occupants Adults

Children ,

1 Number of Deaths

Number of Injured

Number of Non- injured

K

a level

b level

c level

0 level

Level 3 Descriptor Array

Category Class

i Subclass

. _ , ^ Driver Age Over 60 25-59

Under 25

Sex Male

Female

Training None Driver Education

CH.S.)

Commercial

Vehicle Body Type 2 -Door Hardtop

2 -Door Sedan

4 -Door Hardtop

4 -Door Sedan

Station Wagon

Convertible,

Clothtop

24
Level 3 Descriptor Array (Continued)

( Category Class 1 Subclass

Vehicle

i

Body Type ; Convertible, McT;)l

I Top Van

Recreat ional

Small Car (Vnv, etc Compact

1

i Year

1

i

i

i

i

1

i

Model (Safety System)

1

None

1 Point (seat)

2 Point (seat and

shoulder)

3 Point (seat and

shoulder)

4 Point (seat and

shoulder)

Mod 4 point

Air Bag

Energy Absorbing

Steering Col. Dash padding

Bumper

Telescoping Device

Environment Urban Roadways I -System

, Freeways

Primary

Residential

Rural Roadways I -System

Turnpikes

Two and Three lane State

Rural

Month

1

Weekday

Weekend

Time Daylight A.M. Daylight P.M. Night A.M. Night P.M.

Posted Speed Under 25 M.P.H. 30-40 M.P.H.

50-55 M.P.H.

60 M.P.H. Over 60 M.P.H.

25
Level 3 Descriptor Array (Continued)

Category Class Subclass

Accident Factors Manner of Collision • I lead -on

• Side

• Rear

• Overturned

• Struck fixed

object

.

Speed • Above posted

speed

• At posted

speed.

• Under posted

speed

.

Driver Condition BAC > .10 DAC Inattention

None ——- Restraint

Property Damage

•• Number of Occupants Adults

Children

Number of Pedestrians

Injury Severity Occupants

Number of Deaths

Number of Injured

Number of Non- injured

K

a level

b level

c level

0 level

• Pedestrians

Number of Deaths

Number of Injured

Number of Non- injured

K

a level

b level

c level

0 level

26
Tlie highest level of capability is shown as Level 4, and it is identical to Level 7> in all categories except the last. Injury Severity, which is shown here.

Level 4 Descriptor Array

Category Class Subclass

Driver

Vehicle

Environment

Accident Factors

Injury Severity

(Same as Level 3) (Same as Level 3) (Same as Level 3) (Same as Level 3)

Occupants

Number of Deaths

Number of Injured

Number on Noninj ured

Pedestrians*

Number of Deaths

Number of Injured

Number on Noninj ured

(Same as Level 3) (Same as Level 3) (Same as Level 3) (Sanie as Level 3 )

Ki (immediate injuries'

K2 (within 24 hours)

K3 (immediate fire)

a level (critical)

bi (moderate)

b2 (Severe)

bj (serious)

c level (minor)

0

level

level level

0 level

*To be consistent the pedestrian injury-severity subclasses should be the same as for the

motor-vehicle occupants, but it is not mandatory since the intent of the measurement is not the

same in both cases.

5.4.5 Evaluation of Levels of Description

It is possible to construct a large number of levels of descriptor arrays by combining the

category classes and subclasses from different levels. Our evaluation will be only on the four

levels presented above, however. Each level is judged on capability and fulfillment of basic

objectives, requirements for implementation, data collection specifications and requirements,

and the length of time for development of the level as an operational tool. With respect to this

evaluation the basic objectives to be satisfied are: (1) that descriptors be capable of depicting

the National traffic safety situation, (2) that selected descriptors have the capability of

sensing changes in the National situation brought about by standards and designs derived from NHTSA vehicle and safety programs, (3) selected descriptors have the property of division into

subclasses to cover details of interest in the important areas of occupant -packaging systems,

injury-severity levels, human parameters, and factors contributing to accident causation, and

(4) fulfilling a basic need to measure, via indicators, appropriate specific programs for achieving

NHTSA goals of accident avoidance and injury reduction.

5.4.5.1 Level 1 Evaluation

Level 1 consists of twelve classes and nine subclasses, and essentially represents current practice except for the inclusion of two levels of injury severity not presently used in describing

the National situation. The evaluation is as follows:

27
Capability . Equivalent to current practice but extends the emphasis beyond fatalities to include a gross indication of numbers of injured and non-injured.

Objectives . Level 1 is too aggregated to satisfy all of the desired objectives, and certainly

does not meet objectives (2), (3) and (4).

Implementation . The only change from current practice is to include the number of injured

and non- injured in current statistical compilations. This should require no additional cost to NHTSA and appears immediately obtainable and reportable.

Data Requirements . The data is readily available from all reporting States, and from the

data collection system which feeds the SAFEi/and FAFl/ data bases.

Time Horizon . Immediately implementable.

5.4.5.2 Level 2 Evaluation

Level 2 consists of sixteen classes and 36 subclasses, and represents a considerable advance

over Level 1. Ihe evaluation is as follows:

Capability . Level 2 contains all of the essential variables needed to provide a good picture

of the National situation. The principal advances are in reporting injury- severity in five sub- classes, the inclusion of roadway types and the vehicle body-type. If the vehicle safety system

is related to injury-severity as an index a new dimension of the National picture should emerge.

Obj ectives . Level 2 satisfies (1), partially satisfies (2J and (3J, but does not fully

meet the intent of (4)

.

Implementation . Some planning and investment are necessary to obtain the data for injuryseverity and the speed descriptor. These are available from both the SAFE and FAF reporting

forms. Most States provide some information on speeds and all but 15 States now report injuryseverity appropriate for Level 2 description. It is desirable to have full participation, so it becomes necessary to get all States up to standard for reporting this data, and in some cases, getting States to start recording at this level of detail on injury levels and accident factors.

Data Requirements . In principal all of the data for Level 2 is accounted for by the SAFE

and FAF reporting systems. So no additional requirements are necessary.

Time Horizon . The structure of Level 2 lends itself to an early implementation only if the

gaps in data collection from States not reporting on injury severity and accident factors can be

filled quickly. If less than 1001 reporting is acceptable, Level 2 can be implemented very

quickly, otherwise a 6-month to one-year delay should be expected.

5.4.5.3 Level 3 Evaluation

Level 3 consists of 23 classes and 73 subclasses, and attempts to obtain a level of description which begins to reach toward measuring the NHTSA vehicle and traffic safety programs. The

evaluation is as follows:

Capability . Level 3 provides for descriptions and measures of driver education, vehicle

body-type and safety systems, roadway types, driver condition at time of accident and occupant

and pedestrian injury- severity levels. It covers the depiction of the National situation and

permits new indicators to be developed, such as safety-system and injury severity, vehicle bodytype to safety system, vehicle body-type to injury levels and driver condition to accident

causation.

Standard Accident File Extract

2./ Fatality Analysis File.

28
Objectives . Level 3 satisfies (1), serves as a start in obtaining (2J, satisfies (7>j

,

and should have the potential for supplementing the measurement of programs dealing with specific

features of highway traffic safety.

Implementation . The requirements of Level 3 do not differ very much from Level 2, except

for the details on vehicle body-type and vehicle safety-systems. Since accident reports give

the make, year, model and body-type of vehicles, a data base could be developed from which the

particulars of the safety-system would be retrieved. This would require iMlfTSA to establish a safety-system/vehicle file and integrate its function and operation with the SAH- or FAF systems.

Data Requirements . The principal item, over and above Level 2 data requirements, is the

addition of the vehicle safety-system features. This should be made a data reporting requirement by

the automobile manufacturers if it is not already in effect. Compliance with standards should

be reported, as well as devices exceeding required standards.

Time Horizon . About the same as Level 2. The data on vehicle safety -systems should be

currently available. The implementation could be developed in about the same time of six months

to one year, and incorporated into current data processing procedures.

5.4.5.4 Level 4 Evaluation

Level 4 has 23 classes and 77 subclasses. It is the same as Level 3 except for the enlarged

scope of the injury- severity descriptors. The evaluation is as follows:

Capability . Level 4 extends the capability to a finer resolution of injury -severity re- porting. It stops short of the medical categories given in the Collision Analysis Report Form,

Dec. 1971, but does extend the a, b, c levels to more refined definitions than now in use. These

definitions are still reportable by police officers, paramedics, doctors, firemen, etc., and do not require injury specificity.

Objectives . Objectives (1) > (2) and [3) are essentially satisfied; objective (.4) must be

judged on the basis of application of Level 4 data to specific programs.

Implementation . The success of Level 4 descriptions hinges on the safety-system and injuryseverity levels being reported consistently and accurately, at least within acceptable definitions.

The investment for its implementation should not be large; coordination and acceptance are the

principal problems.

Data Requirements . Same as Level 3. The extension of injury -severity levels from five to nine does require modifying current reporting forms and extending field assignments in computerfile data records.

Time Horizon . On the order of two to three years; this covers implementation of safetysystem data file, form changes, data record format changes, and getting the system working smoothly

in the field.

5.5 Program Related Descriptors

In Levels 3 and 4, emphasis was placed upon the inclusion of descriptors that would serve

to measure, and be sensitive to, the specific ^JHTSA priority programs on alcohol and drug abuse,

occupant -packaging, vehicle safety- systems and, to some extent, human factors. It is important

for NHTSA to commence the inclusion of these activities in their statistical compilations since

the investment in these programs, and the goals concerning accident avoidance and injury reductions, can only be ascertained by some form of measurement of this kind. IVhen classes of information as described by Levels 3 and 4, which address vehicle safety-system, roadways, injury- severity and

vehicle-type, are combined and developed as indicators a much clearer picture of the National

situation should emerge. The problem of measurement becomes more difficult, however, when the

priority programs take on greater specificity of detail. When this occurs sensitivity of in- dicators is subject to greater question and some resolution as to measurement and detail must

be made.

29
6.0 Rl-COMMl-MIATTONS

The recommendations are given in five areas: which statistical compl i lations should be

dropped, which areas of analysis should be investigated, which level of capability should be

implemented, suggestions on data development, and exposure criteria. Text references are provitl cd for each recommendation.

Wliat should be dropped

The following rates or descriptors appear to provide no significant insight into the traffic

picture and possess no tangible merit or potential for being useful in measuring program effec

tiveness.

1. Deaths per 100-million vehicle miles by State (see p. 6-8, 19, 20I

2. Deaths per 100,000 population (see p. 8)

3. Leading causes of deaths (see p. 8)

4. Monthly mileage death rates (see p. 8)

Areas of Analysis

(1) NHTSA should study the potential usefulness of statistical analysis based on a subset

of States which correlate closely with National characteristics of traffic behavior. The re- gional approach has certain advantages of improving responses, reporting .standards, higher

level of participation, and a smaller volume of reported data. (See p. 17 et seq)

(2) NHTSA should consider the possible advantages of locating the ASAPs into regional groups consonant with the above proposed statistical regions. This action has the potential

for making the program more effective because of concentration, greater visibility with the public, and providing a better basis for statistical calculations. It might be more meaningful

to evaluate the ASAPs in conjunction with other traffic safety factors pertaining in the region.

(See p. 21)

Levels of Capability

(1) It is recommended that NHTSA implement the capability of the Level 3 Descriptor Array,

or its equivalent, as a first step toward a more complete characterizat ion of the National situation

and measuring the impact of NHTSA vehicle and safety priority programs. (See p. 24. 2S. 2(-), 281 Data Development

(1) Since it appears that the SAFE data base is a subset of the FAF data base it is suggest

ed that some resolution of priority and resource allocation should be made, and the surviving

data base be organized and developed toward a retrieval and reporting capability for purposes of

analysis, statistical compilation and special studies.

(2) The current capability should be expanded to accommodate more descriptors dealing with

program impact and provide an efficient data retrieval system responsive to current and future

needs

.

Traffic Safety

Adopt injury- severity per accident and accidents per vehicle-year , in place of fatalities per vehicle-miles traveled as preferred measures of traffic safety (p. 12-17)

30
APPENDIX

Classification of Statistics on National

Situation

31
APPENDIX

This Appendix presents a categorical arrangement of the data presented in Appendix A of

.'^jinual Report Traffic Safety '72. ilie notes to the tables and figures are given separately

from the tables and figures to emphasize the amount of descriptive information they contain

a^id to suggest comparison as to which supplies more information.

The Figures and Tables of Appendix A of Traffic Safety '72 have been classified by content

into four primary categories. Crash and Damage (CD), Vehicle (.V), Priver (D) and Environment (E) Tliey have been further classified in some instances by secondary categories. In this case, we

have used the additional notation. People (P) , Occupant (0), Pedestrian (Ped) . In some cases

the source of the data has also been indicated, e.g. Federal Highway Administration Statistic

(FHWA), the Bureau of Census (Bu. Cen.).

All references to figures and tables are to those in /^pendix A of Traffic Safety '72.

32
CRASH AND DAMAGE

Title of Figure or Tables Figure/

Table

Sccondnry

Category

Motor Vehicle Deaths by States or Occurrence,

1972 and Percent Change from Period 1966-

1968.

Motor Vehicle Mileage Death Rate, 1972 and Percent Change from Period 1966-1968.

Trend in Motor Vehicle Death Rates, 1950-

1972. Deaths per 100,000 Vehicle Miles

Deaths per 100,000 Registered Vehicles

Deaths per 100,000 Driver Licenses in Force

Deaths per 100,000 Population

Index Trend Comparison Motor Vehicle Deaths

and Industrial Production (1967 = 100)

Pedestrian Fatalities 1950-1972

Motor Vehicle Occupant Fatalities,

1950-1972.

Motor Cyclist Fatalities, 1950-1972

Bicyclist Fatalities, 1950-1972

Bicycle Population Death Rate, 1950-1972

Weekend - Weekday Contrast in Fatality Rates,

1971

Leading Causes of Death by Age 5 Sex, 1969

Monthly Mileage Death Rates, 1970-1972

Motor Vehicle Fatalities per Day by Month,

1955-1972

1955-1959

1960-1964

1965-1969

1970-1972

Leading Causes of Deaths, All Age Groups,

Male and Female, Combined United States,

1969.

Fig. A2

Fig. A3

r Fig. A-4

Fig. A-10

Table A2

Fig. A-5

< Table A2

, Fig. A-5

' Table A2

[Fig. A-5

Fig. A7

Note

Fig. A8

TPig. A-8

"^Table A-4

Fig. A9

Fig. A- Fig. A-11

Fig. A-11

Fig. A-12

Table A-5

Fig. A-13

Fig. A- 14

Fig. A- 15

P,V

D,V

D,V

D,V

D,E

Ped.

0,V

D,V

D,V

D,V

P,E

P

P,V

P,V,E

P,E

33
VEHICLE

Title of Figure/Table Figure/Table

Secondary

Category Source

Motor Vehicle Registration, 1936-1972

Estimated Vehicle Miles Traveled,

1936-1972

Trend in Ratio of (1950-1972)

Licensed Drivers to Registered

vehicles.

Population to Registered Vehicles

Total Ntotor Vehicle Travel

,

1950-1972

Urban BVM

Rural BVM ' ' .

Fig. A-1 Table A-1

Fig. A-1 Table A-1

Fig. A-6

Table A2

Fig. A-6

Table AFig. A-21

(See note)

HflVA Highway

Statistics

FIIWA Statistics

(See Table

A-2)

Bu . Cen

.

FHWA

Vehicle Travel on the Interstate Highway System, 1967-1971

Total, Urban, Rural BVM

Vehicle Travel on Primary Highway

Systems, 1967-1971

Total, Urban, Rural BVM

Vehicle Travel on Secondary Highway

Systems, 1967-1971

Total, Urban, Rural BVM

Average Free -Moving Travel Speed on Main Rural Roads, 1957-1971

Growth in Population and Motor Vehicle

Registration

(by type of Registered Vehicle)

Average Number of Miles Travelled

Annually by Type of Vehicle, 1971

Fig. A- 22

Fig. A-23

Fig. A- 24

Fig. A-25

Table A- 13 Note

Table A- 14

E FHWA

E FHWA

E FHWA

FHWA

FHWA

Bu. Cen.

Note

Types of Motor Vehicles Involved in Fatal and Injury Accidents, 1971 Table A-15 NHTSA Nat. Accident

Summary File

*Note: All the entries above the horizontal line in this table are independent of

fatalities and injuries.

The entry below the line relates to fatal and injury accidents.

34
DRIVfiR

Title of Fifiure/Table Figure/Ta hlc

Driver Licenses in Force 1936-1972 Fig. A 1 Table A-1

Distribution of All Drivers Licenses

in l-'orce by Age Group, 1972 Fig. A IS

l">river Licenses in Force by Age Group,

Male and Female, 1965-1972 Table A7

Percent Increase in Total Number of

Driver Licenses in Force by Age

Group, 1965-1972. Fig. A-16

Distribution of Driver Licenses in Force by Age Group of Men, 1972 Fig. A- 17

Percent Increase of Driver Licenses in Force by Age Group of Men, 1965-72 Fig. A- 18

Distribution of Driver Licenses in Force by Age Group of Women, 1972 Fig. A-19

Percent Increase of Driver Licenses in Force by Age Group of Women, 1965-

1972. Fig. A-20

*

Male and Female Drivers Involved in Fatal

non-Pedesterian Accidents, 1971 Table A- 10

Percent Distribution by Age of Driver

within Accident Type (Estimated)

Male, 1971 Table A-11 Female, 1971 Table A- 12

*Note: All the entries above the horizontal line in the table are independent

of fatalities and injuries.

The entries below the line relate to fatalities only.

ENVIRONMENT

Figure/ Secondary

Title of Figure/Table Table Category Source

Vehicle Travel on the Interstate Highway

System, 1967-1970, Total, Urban, Rural Figure A- 22 V FHIVA

(Same) on Primary Highway System, 1967-1971 Figure A-23 V FHIVA

(Same) on Secondary Highway System 1967-1971 Figure A- 24 V FHWA

35
NOTES

Fig. A-1 Through 1972 there has heen no sign of a slackening in the rapitl growtli in the use ot motor vehicles. Vehicle miles have increased faster than the number of vehicles,

and both liave increased faster than the number of drivers, llius , travel |x i .(. hicle,

travel per driver, and vehicles per driver are still increasing.

Fig. A-2 Tlie pattern of change in motor vehicle deaths since 1966-1969 shovvs a group of

Nfountain States with above-average increases in deaths. These States generally showed

the smaller decreases in vehicle mileage death rates. The only consistent pattern of

decrease over a contiguous area is found as a group of North Central States from

Pennsylvania through Illinois.

Fig. A-3 Without exception, the States have reduced their vehicle mileage death rates. The largest reductions have occurred in a broad belt stretching from Appalachia to Minnesota and Iowa. The smallest reductions have occurred mostly in the Mountain

States.

Fig. A-4 \^ Improvements in vehicles, roads and safety in operation have reduced the death

Fig. A- 10] rate per mile of travel by about 40% since 1950, but the rise in travel has more than

offset this. Nevertheless, the decline in the mileage death rate means that it is now possible to travel 17,000 miles at the same risk as was attained in driving 10,000

miles in 1950.

Fig. A- 7 Increases and decreases in annual highway fatalities have corresponded very

closely with changes in economic activity. These cannot be explained by changes in total vehicle-miles of travel because the vehicle mileage continues to rise, even when fatalities declined. Hence the changes must be due to the nature, rather than

the quantity, of travel mileage.

Fig. A-10 (Same as A-4). .... -

Fig. A- 11 Increasing use of the bicycle has led to higher numbers of deaths and higher

death rates. The bicycle is used much more for adult transportation and recreation

than it was a few years ago, but bicycle death rates are also related to and, in part,

caused by the increasing amount of motor-vehicle traffic mileage.

Fig. A-12 Week-end crashes (4:00 P.M. Friday - 3 A.M. Monday) produce many more fatalities

in the evening and early morning hours than do weekday crashes. This is primarily

a result of increased recreational driving on weekend nights and associated increased use of alcohol.

Fio. A- 13 July through October is the period when the highest absolute number of fatalities

occur, and it is also the period when fatalities per vehicle mile of travel are highest. This is probably a result of the large proportion of recreational travel during

this period. Vehicle occupancy rates in recreational travel are much higher than for other purposes and so the chance of a fatality per accident is higher.

Fig. A-14 The seasonal pattern of motor vehicle deaths has shifted gradually over the years

from a yearly peak in December to a high period that extends from July through October.

This most probably reflects the increased amount of recreational travel by the American

public during the summer and early fall.

Table A-6 If you survive the hazards of early infancy, but your life ends earlier than it should, there is a great chance that a motor vehicle accident will be the reason than

any other major killer. Motor vehicle accidents are the leading cause of death for young people from late childhood to the early thirties. A large group of men the

same age will be in their forties before another killer (heart disease) will have

killed more of them than died in motor vehicle accidents. A similar group of women

will be in their early forties, \A\en cancer overtakes motor vehicle accidents as the

biggest total killer of the group.

36
Fig. A-16 Changes in the age distribution of licensed drivers are an important element

of the highway safety problem. In recent years the largest increases have occurred

in those age groups when accident rates have been higher than average.

The number of licensed drivers in the youngest and the older age groqis have

increased much more than those in the middle group, aged 30-59. The total number

of drivers increased 20% during the period 1965-1972, but the increase was 36" in the 20-29 age group, and 43% in the over-60 grou}). There was an increase of 12,194,000

female drivers, or 30%, while (male) drivers increased by only 7,504,000 or 131, so that in the seven-year period the ratio of male to female drivers declined from 3 to

2 to 5 to 4.

A very large increase occurred in elderly women; the number of female licensed

drivers 60 and over increased by 5,360,000 or 80%.

Fig. A-21 Travel in urban areas has been increasing slightly faster than travel in rural areas in recent years, but the proportions vary considerably among major road systems. On the Interstate System there is a nearly equal division between urban and rural

travel mileage. On the Primary Systems there is more rural travel, with a 57-43

split in 1971 mileage, while on the Secondary Systems there is more urban travel,

the proportion being 42-58 in 1971.

The distribution of the total 1971 travel of 1.19 trillion miles among Interstate,

Primary and Secondary Systems was 15%, 34% and 51%.

Table A-10 Males aged under 25 are disproportionately involved in all types of accidents.

The over -representation is greatest for single-vehicle accidents, especially "over- turn in road." Female drivers in this age group show the same pattern of over re- presentation, although to a lesser degree. Drivers in the age group 25-64 are gen- erally in fewer accidents than would be expected on the basis of their numbers. Drivers over 64 show a mixed pattern, with an over -representation of female and under-representation of males, relative to the number of licensed drivers in that age group.

Fig. A-25 Over the 10 years from 1961-71, the average speed of vehicles on the main rural

roads increased about 13%. A corresponding increase in crash speeds occurred. This

has been a significant factor in the rise of highway deaths, because high-crash speeds

increase the chances that a fatality will occur.

Table A-13 The rate of increase for motor-cycles (registration) continues to be far higher

than the growth rates for other vehicles. Numbers of commercial vehicles, such as trucks and buses, are growing relatively faster than passenger cars. The number of

conmercial buses has begun to increase more rapidly than in the 1960's.

Table A- 14 About four miles out of five are driven by passenger cars, and trucks account

for almost all the remainder. Travel per passenger car topped 10,000 miles for the

first time in 1972. School-bus travel increased only a modest 5%. The basis for

estimating motorcycle mileage was changed in 1972, so that a 50% higher estimate

resulted. This does not represent a change in the basic trend.

Table A-15 Motor cycles and buses are over-represented in fatal accidents. Motorcyclists

in a crash receive essentially no protection from their vehicles. The most probable

explanation for the buses over -representation is the larger number of occupants in- volved per crash.

The ratio of killed to injured in crashes involving trucks is greater than for other motor vehicles, most probably due to the greater weight of trucks.

37
NBS-1 UA (REV.

U.S. DEPT. OF COMM. mm \nc.BAPH\r data

SHEET

1. PllHl.K A 1 ION OK Kl I'OK 1 NO

NBSIR 74-561

2. O.iv'r -V- . I -.-, No

3. K, , ipii iii 's Ai 1 1, .s^.,,>n No.

4. TlTl.K AND SUPTITLH

Analysis of Methodology for Measuring

wationai. nignway irattic barety

5. Puhluation Date September I974

6. PertiiriTiing Organisation i odi 431,00

7. AUrilOR(S)

Robert G. Hendrickson, Alexander R. Craw

8» t* r f v > r III 1 ri ^

^^r^tiii- J^t*|*'.)rt ?^(>.

9. [PERFORMING ORGANIZATION NAME ANO ADORl-.SS NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Proie.t 'Task 'Worl. Unit No. 4314496

11. f onii.ict Grant No

12. Sponsoring Organization Name and Complete Address (Street, City. State, ZIP)

National Highway Traffic Safety Administration

Dept. of Transportation

400 7th Street, SW. , Washington, D.C, 20590

13. T> in ,( Repori \ 1' r i o .!

( ov : e.l Final Report

14. ^pon 'ling Agi-n > ,.1.

15. SUPPLEMENTARY NOTES

I 16. ABSTRACT (A 200- word or less (actual summbrv of most sigfiidcant information. If document includ'^ a : if^niticunt ! bibliography or literature survey, mention it here.) \ This report covers a critique ol' current measures used by NHTSA to repoi t and

evaluate National Traffic Safety , and presents the development of propoted acasures

for evaluating the impact of NHTSA priority programs on the vehicle--dri\ ir-highway

mix. The proposed measures emphasize the use of injury-severity levels aiid an extended set of driver-vehiclt-highway descriptors to depict critical fa< tors in

National traffic patterns and treads. The conclusions and recommendations address

extensions of current indicators to describe accident phenomena by drivei and

vehicle attributes, to enlarge tiie number and detail of descriptors of accident

data and accomodate these extensions by more comprehensive data development.

Surrogates for National statistics and concentration of certain programs were

investigated.

17. KE\ WORDS (six to twelve entries; alphabetic ai order; capilalize only the first letter of the first kev word unltss a proper name; separated by semicolons

)

Highway traffic safety; traffic data sy&tems; safety program impact; indicators

18. AVAILABILITY ["X Unlimited 19. SECURITY CLASS

fTHiS REPORT)

21. NO. OF PAGES

|3_ For Official Distriburion. Do Not Release r.. NT IS UNCI. ASSIFIED

37

[2 ' Order From Sup. of Doc, U.S. Government

Washington, D.C. 20402. SD Cat. No. C;n

'tinting Office 20. >.[( UlUTY CLASS

'TH1:> PAGE)

22. Price

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USCOMM.DC 29042-P74