Characteristics of traffic crashes among young, middle-aged, and older drivers

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Abstract

An overview of the characteristics of traffic crashes among young, middle-aged and older drivers is presented. The results suggest that the youngest and the oldest drivers were more likely to be considered at-fault. With respect to crash characteristics, older drivers were less likely to have crashes involving driver fatigue, during the evening and early morning, on curved roads, during adverse weather, involving a single vehicle, and while traveling at high speeds. Conversely, older drivers were over-represented in crashes at intersections and/or involving failure to yield the right of way, unseen objects, and failure to heed stop signs or signals. Crashes occurring while turning and changing lanes were also more common among older drivers. Alcohol was less likely to be a factor in traffic crashes involving older adults. Synthesizing these results led to the conclusion that the primary problem with the young is risk-taking and lack of skill. The strength of older drivers lies in their aversion to risk, but perceptual problems and difficulty judging and responding to traffic flow often counterbalance this attribute.

Introduction

The safety of older drivers has received heightened attention in recent years. This is due to two primary factors: traffic crash statistics for older drivers and demographic shifts in the US population. As a group, older drivers have one of the highest crash rates per vehicle mile of travel (Cerrelli, 1989, Cerrelli, 1992, Retchin and Anapolle, 1993, Massie et al., 1995). Moreover, the incidence of traffic crashes involving injury and fatal traffic crashes increases sharply after age 55. In 1996, there were approximately 34 million adults aged 65 years or older, representing 12.8% of the US population, about one in every eight Americans (Campbell, 1996). The number of older adults increased by 2.6 million or eight percent since 1990, compared to an increase of 6% for the under-65 population. These increases are expected to continue though the year 2030, at which point the proportion of the US population aged 65 years and older will have increased to 21.8%.

As a consequence of this demographic shift, an increased number of older adults will be on the road and driving. In fact, it is likely that, proportionately, the growth in the older adult driving population will be larger than the growth of the older population itself. This is expected because the proportion of older adults, particularly females, with driver’s licenses is also expected to increase. It is also likely that older drivers will continue to increase their individual traffic exposure by driving more.

A number of studies have attempted to identify risk factors for traffic crash involvement among older drivers (Hu et al., 1993, Janke, 1994). Most have focused on chronic medical conditions and functional impairments. The former studies have received attention because the prevalence of most chronic medical conditions increases with age. Case reports of traffic crashes resulting from acute manifestations of chronic conditions (e.g. hypoglycemic attacks) have also supported research in this area (Sturner and Sullivan, 1983). Further, specific medical diagnoses have received additional attention, since they are often associated with impairment of skills necessary for successful motor vehicle operation.

Research studies have also focused on functional impairment (e.g. vision, cognition, and mobility) (Hu et al., 1993, Janke, 1994). It has been argued that functional impairment may be less heterogeneous than specific medical diagnoses when it comes to classifying at-risk drivers (Sims et al., 1997). That is, functional limitations can result from many medical conditions whereas not all persons with such medical conditions are likely to be functionally impaired. Driving regulations based upon specific conditions may inappropriately penalize drivers who pose no increased risk to the traffic environment.

Traffic crashes represent a heterogeneous collection of events. That is, traffic crashes occur within a matrix of temporal, environmental, locational, and maneuver circumstances. Characterizing the nature and circumstances of traffic crashes may provide insight as to potentially problematic aspects of the driving environment. There are factors that indicate that some crashes are due to risk-taking on the part of the causal driver (e.g. speed, driving at high-risk times, alcohol usage, and other unsafe-act indicators). Other factors can be used to classify crashes as being either forced or unforced. Single vehicle crashes are obviously unforced, while those that involve complex interactions between vehicles in traffic might have contributed to or in some way ‘forced’ the error. Differences in these factors by age may suggest aspects of the driving environment that are more hazardous for different age groups. This information can serve to enhance etiologic studies by associating suspected functional impairments to the physical characteristics of traffic crashes. For example, the finding that older drivers are disproportionately involved in crashes where they misjudged stopping distance may suggest visual impairment as an important etiologic factor. Finally, differences in traffic crash characteristics can inform those in the traffic engineering and ergonomics how they might adapt features of the driving environment to accommodate the needs of an older driving population.

A number of studies in the United States and Finland have compared the characteristics of traffic crashes among older and younger drivers (Planek and Fowler, 1971, Cooper, 1990, Hakamies-Blomqvist, 1993, Hakamies-Blomqvist, 1994a, Hakamies-Blomqvist, 1994b, Hakamies-Blomqvist, 1994c, Hakamies-Blomqvist et al., 1995, Stamatiadis and Deacon, 1995, Stamatiadis, 1996). In general, these studies consistently find that older drivers have mileage-based crash rates that are as high or higher compared to younger drivers. It has also been reported that crashes among older drivers are more likely to occur in good weather, during daylight hours, at intersections, when making turns. Older drivers in crashes are also more likely than middle-aged drivers to be considered the casual (i.e. at-fault) driver. Alcohol involvement has been reported to be much less of a factor in traffic crashes among older drivers. Crashes among young drivers are more likely to involve a single vehicle, to involve one or more driving errors, to have speed as a factor, and involve alcohol.

Most of the prior literature in this area has focused on fatal crashes. While these outcomes are the most grave, they represent the smallest proportion of all crash events by severity. When attempting to gain an understanding of the problematic aspects of the driving environment, consideration of only fatal crashes may prove restrictive or worse, provide a biased representation of crash characteristics. For example, generally fatal crashes are more likely to involve alcohol and to occur during the evening and early morning. At least one author has concluded, based upon data from Finland, that the characteristics of fatal crashes are fairly generalizable to all crash events (Hakamies-Blomqvist, 1994b). However, a study in the United States reported a number of driver and crash factors related to fatal crash involvement (Cerrelli, 1997). Male gender, higher age, moderate or high vehicle speed, weekends, night-time, side impact collisions, single vehicle collisions, and head-on collisions were all identified as being positively associated with fatal crash involvement relative to non-fatal crashes. Of the studies that have included all crash events, no one has evaluated a broad range of crash characteristics and few have taken the issue of fault when assessing differences across age.

The goal of this paper is to present the comparison of traffic crash characteristics of young, middle-aged, and older drivers in order to derive some basic principles that will be applicable to most areas of countermeasure development. Data used in this study consisted of all police-reported crashes occurring in the state of Alabama during 1996.

Section snippets

Crash characteristics

We accessed information on all police-reported traffic crashes occurring in the state of Alabama during 1996 (N=136 465). This was furnished by the Crash Analysis Reporting Environment (CARE), a World Wide Web (WWW)-based on-line crash data analysis system designed to assist traffic safety professionals in developing more effective traffic accident countermeasures (http://care.cs.ua.edu). It is currently prototyped and being tested with Alabama, Tennessee and the NHTSA Fatality Analysis

Crash rates

Fig. 1, Fig. 2 present rates per 100 licensed drivers for all and injurious/fatal crashes by age and gender. In both Figures the crash rates are elevated for younger drivers and steadily decline with age. Males have higher rates than females at all ages. The rate for fatal crashes follows a similar pattern although there is a slight increase among drivers aged 75 years and older (Fig. 3).

Crash rates per PMT are presented in Fig. 4Fig. 5Fig. 6. For all crashes, the rate per 100 000 PMT is

Discussion

This section will discuss the findings given above by comparing these findings both to each other and to findings of similar studies in the literature. The categories are generally as given above.

Acknowledgements

The authors thank Cynthia Owsley, Ph.D. for commenting on an earlier version of this paper. This study was supported by NIH grants P50 AG11684 (the Edward R. Roybal Center for Research in Applied Gerontology), and R01 AG14684, and the Alabama Department Economic and Community Affairs, Traffic Safety Section.

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