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ON-ROAD TESTING

Naturalistic Studies (Driving In Traffic) continued...

Visual attention accounted for 18 percent of the variance on the road test after controlling for the effects of visual acuity, and was associated with over half of the specific driving maneuvers. The authors point out that the maneuvers with the greatest association with visual attention (scanning the visual field for potentially dangerous obstacles, maintaining one’s speed and distance with respect to other vehicles, yielding the right of way, and negotiating turns or merges safely) are also those most often associated with older driver crashes. These results suggest that driving tests to determine the effects of medications should include these maneuvers, to increase sensitivity for visual attention deficits.

An on-road standardized driving test was used by Wild and Cotrell (2003) to compare actual driving performance to self-reported and caregivers’ perceptions of driving ability for a sample of 15 healthy elderly subjects and 15 elderly subjects with mild Alzheimer’s disease (mean age = 72.7). Caregivers generally included spouses or other family members living with the driver, or close friends (in the case of a subset of the healthy elderly). Criteria for participation by the healthy elderly controls (recruited from the Oregon Brain Aging Study) was a Clinical Dementia Rating (CDR) score of 0, independence in daily activities, no chronic medical conditions, and not taking any medications that affect cognition. Alzheimer’s disease patients were recruited from the Aging and Alzheimer Disease Clinics and the Portland Veteran’s Administration Medical Center. Nine of the Alzheimer’s disease (AD) patients had a CDR score of 0.5 and 6 of the AD patients had a CDR score of 1. All subjects were required to have a valid automobile driver’s license, health and automobile insurance, and drive a minimum of once a week.

Prior to participation in the road test, subjects in the Wild and Cotrell study were advised that they would be referred to the DMV for further evaluation if their driving performance was of concern to the evaluator. Of all patients contacted, 16 declined, giving reasons such as lack of interest in the study or inconvenience due to scheduling conflicts or distance required to travel. While acknowledging a possible selection bias against less confident or less able drivers, i.e., due to the fear of losing their driving privileges, the authors cite other researchers who have been successful in recruiting subjects with a wide range of deficits and driving abilities in similar research (Hunt et al., 1993; Carr et al., 1991).

The principal relevance of this study to the current study topic lies in the cognitive abilities necessary for safe driving. Drivers with mild dementia have been reported to have a crash rate that is only slightly higher than drivers of all ages in the United States, and well below that of drivers age 16 to 24, during the first three years of the disease (see Staplin et al., 1998 for a review of dementia and diminished driving skills). Side effects of commonly used CNS medications include cognitive impairment (sedation, decreased alertness, poor concentration, mental slowing or confusion, impaired judgment) while under the influence of the medication. The road test used in this study was sensitive to the effects of cognitive decline associated with AD, and could also, theoretically, be a sensitive measure of the effects of cognitive decline associated with medications.

The on-road driving evaluation in the Wild and Cotrell (2003) study was conducted by a certified driver rehabilitation specialist (CDRS) in a dual-controlled automobile, on a standardized test route in a residential neighborhood in an area unfamiliar to participants. The route included intersections, lane changes, stop signs, and traffic signals, and segments at pre-determined intervals when the evaluator engaged the subjects in conversation to determine ability to attend to driving, navigation, and engaging in conversation simultaneously.

The driving evaluation began with a 30-minute familiarization with the test car, followed by approximately 60 minutes of on-road test time. Drivers were evaluated using a 10-item assessment that is an abbreviated version of the assessment used at the Portland Oregon Veteran’s Administration Medical Center. Items were selected to represent the most frequent driving errors and causes of crashes among patients with AD as well as older drivers in general; many of the items follow the Oregon DMV guidelines for driving evaluations. The 10 items, listed below, were rated on a 5-point scale from “very good” to “very poor.”

  • Manages intersections
  • Manages lane changes
  • Maintains lane position
  • Maintains proper speed
  • Follows at a safe distance
  • Signals in time
  • Uses mirrors appropriately
  • Responds to road conditions
  • Responds to warning road signs
  • Handles conversational distraction
 

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