Engineering Factors in Alcohol-Involved TrafficAccidents

A Ithough the number of traffic accidents each year has been substantially reduced over the past decade, highway crashes continue to be a serious problem in the United States. In 1983 approximately 42,400 persons died in highway crashes, and 2 million suffered nonfatal injuries. The 217. reduction in annual highway fatalities and the 367. reduction in the highway fatality rate (fatalities/lOO million vehicle miles) since 1973 are due to a variety of vehicle and highway improvements’ and possibly to stronger traffic laws and enforcement. Through crash testing and detailed study of individual crashes, it has been shown convincingly that vehicle improvements reduce crash frequency and, perhaps more importantly, reduce the severity of crashes that do occur. Numerous studies have also documented the crash frequency and severity reduction features of highway design and operational improvements. A principal difference between vehicle improvements and highway improvements is that the former provide benefits anywhere the vehicle is driven, while the latter enhance safety only at the locations where they are implemented. Since at least the 1920s, the burden of responsibility for highway crashes has been placed on the driver. The logic behind this approach is that most crashes occur as a result of easily identifiable human errors. In reality, there are often vehicle andlor highway deficiencies, but they are typically more subtle and are therefore overlooked by the investigating off icer. It was not until the mid-1960s, when the annual highway fatality toll approached 55,000, that the popular press and congressional hearings focused attention on the deficiencies of vehicles and highways. The point was made that it is much easier to change vehicles and highways than it is to change drivers or pedestrians. Although highway fatalities would undoubtedly decrease if drivers always obeyed traffic laws, always used restraint systems, or for that matter, were made more resistant to injury, it is unlikely that significant advances can be made in these areas. Studies have found that alcohol is involved in approximately half of all fatal highway crashes.” When this statistic is reported by the news media, it is often stated that “drunk drivers cause 500/. of the highway fatalities.” There are three basic difficulties with this statement. First, from a semantic viewpoint, there should be a distinction between “had been drinking” and “drunk.” The law makes this distinction by specifying that a driver with a blood-alcohol level of O.lOA or more shall be presumed to be under the influence of alcohol.’ Second, the statement overlooks the contribution from pedestrians, who account for 18V0 of the highway fatalities. Third, the most critical shortcoming of typical media statements involves the concept of accident “causes.” If a driver is legally intoxicated, this condition may have contributed to crash occurrence. On the other hand, stating that this condition “caused” the crash implies that a sober driver would not have had an accident under otherwise similar conditions. Previous in-depth studies of individual crashes have usually found that a variety of human, vehicular, and highway defects contributed to crash occurrence. The role of highway engineering is to provide a safe environment for the transportation of people and goods. improvements are continually being made to the highway system. Although the most dramatic examples are new highway construction, instances of roadway redesign and spot improvements are much more numerous. These smaller improvements include upgrading signs and markings, resurfacing roadways and shoulders, improving sight distance, and enhancing roadside safety. Certain projects can lower crash frequency, while others can reduce crash severity. Although no countermeasure can guarantee to eliminate accidents, many have been found to reduce certain accident types by 30-600/.. Within the substantial body of literature documenting the benefits of highway safety improvements, there is no indication that the benefits accrue disproportionately to sober drivers.’ In other words, because these improvements provide an environment where the consequences of human error are less serious, they are of benefit to all road users.