Title Banner - Alcohol and Highway Safety 2001: A Review of the State of Knowledge

1. Introduction

This report is a comprehensive review of the state of knowledge of alcohol-impaired driving. The review covers the entire spectrum of related research, from the nature of the societal problem created by alcohol-impaired driving on through the description and effects of programs that have addressed that problem. The review covers scientific literature published since 1990. A special review of the scientific literature about drivers who have been convicted more than once of driving while impaired by alcohol (DWI) was also performed under this contract, and has been published as a separate report (Jones and Lacey, 2000).

BACKGROUND

More than thirty years have passed since the first comprehensive review of the state of knowledge about alcohol and highway safety conducted by the U.S. Department of Transportation (1968). NHTSA has sponsored three updates of the landmark 1968 study, the first published in 1978 (Jones and Joscelyn, 1978), the second in 1985 (U.S. Department of Transportation NHTSA, 1985), and the third in 1989 (Jones and Lacey, 1998a). The 1978 update was a complete re-work, both in form and content. It re-examined the literature used in the prior review, added new material published since 1968, and developed a new structure for integrating and synthesizing the material.

The 1985 update had more modest objectives. Called an "interim update" by its author, it included the "most clearly important studies and findings from the period from January 1978 to December 1982," and left "large portions of the original. . .intact." The 1985 update included the citations from the 1978 report in a separate section from the citations used in the 1985 report. Together, the two reports contain some 500 citations.

The third and most recent NHTSA-sponsored comprehensive review (Jones and Lacey, 1989) covered the same subject matter as the 1978 review, but its focus was more restricted, concentrating on trends and new developments in the field since 1978.

Shortly after completing the 1989 review, NHTSA sponsored an in-depth review of the literature on alcohol-crash countermeasures published during the period 1980-1989 (Jones and Lacey, 1991a; Jones and Lacey, 1991b). This review was the first of the NHTSA-sponsored reviews to incorporate separate critical reviews of each of the more important documents, most of which were cited in a synthesis of the literature.

The last NHTSA-sponsored review (Jones and Lacey, 1998a) was limited to research dealing with characteristics of drinking-drivers and drinking-driving that are associated with increased levels of alcohol-crash risk and/or alcohol-crash incidence. It covered the period 1989-1994.

Two other comprehensive treatments of the subject have been conducted since 1978. The first was the report of the Presidential Commission on Drunk Driving (1983). It incorporated commentary and opinions, as well as literature, but its objective was to generate action rather than to provide an integrated source of information.

The second examination of the entire subject occurred shortly after the 1984 update was published. The vehicle was an international conference sponsored jointly by The Johns Hopkins Medical Institutions and the Alcoholic Beverage Medical Research Foundation. The U.S. Department of Transportation and the National Safety Council were co-sponsors. The results of the conference were published in the conference proceedings (Turner, Borkenstein, Jones et al., 1985). Ten years later, Wagenaar, Zobeck, Williams, et al. (1995) attempted a meta-analysis of evaluations of countermeasures employing one or more components of the criminal justice system, and gave rough estimates of the effects of broad categories of countermeasures. However, the lack of data needed for such an analysis, plus several other factors, precluded a rigorous analysis of the effects of the countermeasures.

Other reviews of varying quality have been conducted since 1978, but their scope has been more restricted -- see, for example, (American Bar Association, 1986). Meanwhile, the level of activity in the field since 1989 has been high. Citizen activist groups have continued to play a large role in stimulating new legislation, and there has been increased emphasis on drinking-driving by other elements of the Traffic Law System. Most important, there has been a very large increase in both quantity and quality of evaluative research, much of which has been sponsored by NHTSA. This report draws together new research in all pertinent areas and places it in perspective in the spirit of the 1978 and 1989 reports.

SCOPE AND APPROACH

The first scientific studies of the alcohol-crash problem in the United States began to appear in the 1930s. One of the first of these (Heise, 1934) defined the four basic approaches to studying the alcohol-crash problem, viz.: 

  1. measurement of the amount of alcohol in the body, 
  2. measurement of alcohol effects on human performance in a laboratory setting, 
  3. measurement of alcohol effects on actual driving performance, and 
  4. estimation of alcohol usage among various populations of drivers.

The 1978 update noted that these four approaches were still being followed, and indeed, they are still being followed today, although approaches 2 and 3 are sometimes combined into a single, "experimental," approach.

In addition to defining the alcohol-crash problem, solutions to the problem were being sought as it was currently understood. The 1978 report observed:

"Early efforts at prevention and control in the U.S. were, with few exceptions, nonscientific and noncomprehensive. Moreover, few alcohol safety programs in this country have been formally evaluated. However, the effectiveness of several alcohol safety programs in foreign countries has been examined with some care, so that there is at least an initial knowledge base on means of dealing with the problem." (p. 3).

As indicated above, this is no longer the case. There is now an extensive scientific literature on alcohol-crash countermeasures, much of which has been published in recent years.

This report deals with both of the major areas alluded to above, the alcohol-crash problem and possible solutions to that problem. The first area, the alcohol-crash problem, is discussed in three chapters, covering the approaches set forth by Heise, but in a different order that is consistent with prior state of knowledge reviews. First, in Chapter 2, we present a broad overview of the epidemiologic literature addressing crashes in which drivers, pedestrians or bicyclists have measurable amounts of alcohol in their blood. Both the number and risk of such crashes are examined in order to obtain an estimate of the magnitude of the alcohol-crash problem nationwide. In the next chapter, we examine in more detail how alcohol affects people and degrades their performance in driving or walking in ways that may lead to crashes (Chapter 3). Then, in Chapter 4, we describe the characteristics of individuals who drink and drive.

The second major area of this review is concerned primarily with alcohol-crash countermeasures that have been tried and evaluated. This material is presented in a single chapter (Chapter 5), which defines several types of countermeasures and discusses the impact of specific countermeasure programs of each type. The possible impact of other countermeasures that have been proposed but not implemented or evaluated is also discussed briefly.

Next, we examine possible future directions of the alcohol-crash problem over the remainder of the decade (Chapter 6), and then present our conclusions and recommendations of the study (Chapter 7). An extensive bibliography containing references cited in the review and other pertinent documents not cited is presented following Chapter 7.

We have exercised considerable care in selecting the materials used in this report, concentrating on the most scientifically reliable studies that are available to the general reader. The main focus is on studies relevant to the alcohol-crash problem in the U.S., but some studies from other countries are included as appropriate. Sources include both collections and individual documents that have not been placed in traditional collections. Types of repositories that were contacted include:

The University of Michigan Transportation Research Institute (UMTRI) library was the central focus and coordinating element of the literature search and collection activities. This facility now has a collection of some 90,000 documents relating to highway safety, not including some 50,000 on microfiche. We also searched the internet for pertinent documents using such search engines as Altavista and Yahoo.

As indicated above, the emphasis was on documents published since 1990, but some earlier studies are included where needed to provide perspective and a basis for comparison with more recent studies. Also, some studies have been reported in more than one document. We have cited only one of the documents for such studies.

Not all of the studies identified in our literature search are discussed in detail in the review. We have sought those studies that best illustrate current thinking and have looked for background material from earlier research that led to current thinking. For the most part, the treatment is from the perspective of the traffic safety generalist, with departures into more specialized technical matters occurring only when these matters are central to the subject under discussion. The reader is asked to refer to the studies cited for a more detailed treatment.

Finally, we have emphasized literature that defines alcohol-crash involvement and risk objectively in terms of the blood alcohol concentration (BAC) of the individuals that were studied. Exceptions to this rule include studies based on well-designed surveys and some studies that measure impairment or alcohol-crash involvement by the opinion of a police officer who investigated the crash. Studies have used a variety of units for measuring BAC. In this review, we use percent alcohol, weight per unit volume of blood, as the unit, and have converted BACs measured in other units to this unit. Thus, in our units, a BAC reported as .05% or .05 would be interpreted as .05 grams of alcohol per 100 milliliters of blood.