METHODS TO MEASURE
Alvarez and del Rio (2002) indicate that the need to identify suitable tests for evaluating the effects of drugs on driving ability has been widely recognized for over 20 years. This sentiment reflects the limitations of crash-based studies, namely, the relative scarcity of measurable events for any but the largest study samples, observed over significant periods of time; and is compounded by underreporting and irregularities in reporting practices across jurisdictions. As alternatives to crash data analysis, Roenker et al. (2003) have examined the strengths and weaknesses of two approaches for measuring driver performance—road tests and driving simulators.
Road tests have long been considered the gold standard for measuring driving ability. They have widely recognized limitations, however. In addition to inconsistencies in the administration and scoring of the results, which presents a major challenge to standardized and objective assessments, as a rule examinees are not exposed to the most risky and demanding situations where driving errors that lead to crashes are most likely. Nevertheless, Ramaekers (2003) asserts that actual driving tests are essential to conclusively define the potential impact of drugs on driving. This review will include both on-road (in traffic) and closed-course methods.
Driving simulators have been touted as offering experimental control for driving performance evaluation; they have also been criticized for a lack of fidelity for many aspects of actual driving (and therefore poor generalizability to conditions outside the laboratory), as well as simulator sickness (particularly for older adults). Another difficulty in evaluating the utility of this method is the ambiguity attached to the term “driving simulation.” Testing systems bearing this label range from actual vehicles on motion platforms with fully interactive control over high-resolution “virtual” environments, to “driving bucks”—a single seat with basic wheel and pedal controls for user inputs—that offer a more limited display of the driving environment and little or no motion, to desktop computer graphic/video presentations of selected driving scenarios for “part-task” measurement (e.g., visual search, hazard detection). This review will consider three categories or levels of simulation, as elaborated in the following discussion.
As one additional perspective, a combination of approaches to investigate the effects of medications on the ability to drive has been advocated by Álvarez and del Río (2002). These authors note that relevant psychological and functional capabilities can be analyzed using vigilance and performance tests, psychomotor test batteries, reaction tests, etc., but should be complemented by simulator and on-road studies. Similarly, Keller, Kesselring, and Hiltbrunner (2003) offered the opinion that psychological tests in combination with an on-road test allow for a balanced judgment of a patient’s fitness to drive. Their psychological assessment (including cognitive tests, a tracking task with divided attention, psychomotor tests, and assessments of impulse control and spatial orientation), when compared to the results of an on-road test, yielded consistent results in 88 percent of the cases studied (38 of 43 patients with neurological disabilities). Keller et al. (2003) also cite other researchers (Sundet, Goffeng, and Holt, 1995) in concluding that, while a psychological assessment sheds light on a subject’s perceptual efficiency, goal-oriented behavior, distractibility, psychomotor efficiency, and impulse control, a road test is key to demonstrate the subject’s capacity to retrieve from procedural memory the technical skills of handling a car, the capacity to allocate and shift attention, and to keep a general overview of concurrent events, all of which are required for safe and successful driving.
The following pages offer a more detailed description of driver performance measure-ment methods employed in recent studies, that may have value in future applications for research on medications and driving.