Banner -- Identifying Strategies to Collect Drug Usage and Driving Functioning Among Older Drivers


Level III: Interactive, Computer Graphic Visuals, Full Motion

This level of simulation is exemplified by NHTSA’s National Advanced Driving Simulator (NADS) at the University of Iowa, and by facilities at a number of automobile manufacturers (e.g., Ford, DaimlerChrysler). A complete vehicle is mounted on a (at least) six-degrees-of- freedom motion platform that provides realistic cues for all vehicle maneuvers experienced in the simulator. A full, 360° field of view is available, using projected computer graphic images (CGI) that are redrawn at 60 Hz or better with no perceptible delay between a control input (e.g., steering wheel movement) and a change in the external (simulated) environment. Resolution of the CGI displays is not “photo-realistic,” limiting certain kinds of studies (e.g., sign legibility), and real-world contrast gradients are difficult to obtain, which may pose a challenge for nighttime driving simulations; but these are fully immersive virtual environments that—theoretically—should allow measurement of almost any driver behavior that could be monitored in the real world, plus high-risk situations to which a subject can only be exposed to in a simulator.

Contacts with a representative of the National Advanced Driving Simulator facility at the University of Iowa were made during this review.43 These revealed that, while this facility has been used to investigate the effects of drugs and medications on driving, all recent studies of this nature have been funded by private industry sponsors, and the specific research designs as well as the results are regarded as proprietary information. An earlier study of interest using the Iowa Driving Simulator (IDS), a precursor to NADS, was identified in the technical literature, though.

Weiler et al. (2000) used the IDS in a randomized, double-blind study to measure “coherence” – a subject’s ability to continuously match variations in the speed of a car the driver is following – among individuals dosed with the antihistamines fexofenadine (60 mg) or diphenhydramine (50 mg); with alcohol (.10 BAC); or with a placebo. Secondary measures obtained in the IDS included lane keeping (steering instability and center line encroachments) and the latency of response to a vehicle that unexpectedly blocked the lane ahead. Subjects also provided self-reports of drowsiness. It should be noted, however, that no older subjects participated in this study; the sample ranged in age from 25 to 44.

The principal conclusions in the Weiler et al. (2000) report were that subjects had significantly better coherence in car following after taking alcohol or fexofenadine than after taking diphenhydramine. Alcohol impaired the secondary tasks, especially response time to the blocking vehicle, but overall driving performance was poorest among the study participants who took the diphenhydramine. Self-reports of drowsiness were not a good predictor of impairment on the primary or secondary tasks in this study. Based on these results, the report authors issue a special caution regarding the use of “first-generation” (sedating) antihistamines, suggesting that they “… may have an even greater impact than does alcohol on the complex task of operating an automobile.

While this study illustrates the potential applicability of high-end simulation methods to future investigations into the effects of medications on driving, a number of criticisms about this work voiced in letters to the editor of the Annals of Internal Medicine, where the study was published, also deserve mention. One body of criticism concerns the primary dependent measure, coherence, citing evidence that this measure of driver performance bears a weaker relationship to safety than the related measures of “modulus” (amplitude of response) and, especially, the delay in a driver’s response to a speed change by a lead vehicle. Other criticisms draw attention to the fact that the research was funded by the manufacturer of fexofenadine, and that two of the authors are consultants to this company.

Perhaps more pertinent to the present discussion are problems associated with older subjects and prescription drug use that have been encountered across a wide range of studies conducted at IDS/NADS. As per the contact identified above, particular care must be taken with older people to ensure that any/all drugs/medications they are taking have been metabolized well past the point of peak concentration, because it is their experience at the Iowa facility that many medications make older people more susceptible to simulator sickness. Subjects’ consumption histories for at least 12 hours prior to study participation are accordingly taken into account. This experience would seem to point to what is, at least potentially, a serious challenge to future NHTSA studies where the explicit goal is to investigate the effects of drugs and medications on the driving behavior of older people.

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43 Pers. comm.. from Dr. Ginger Watson to L. Staplin via telephone conversation March 4, 2005.