Traffic Tech #197: Older Drivers Have Some Problems Negotiating Intersections

OLDER DRIVERS HAVE SOME PROBLEMS NEGOTIATING INTERSECTIONS

One of the principal concerns surrounding older drivers is their ability to safely maneuver through intersections. About one-third of the fatalities of older drivers occur at intersections, and this figure jumps to more than half for drivers over the age of 80. Older drivers may have greater difficulties at intersections because of diminished capabilities, which hamper their selection and execution of appropriate driver responses. Deficits in vision and vision-dependent processes that probably have the greatest impact on older drivers include diminished spatial vision, the functional or "useful" field of view, and depth and motion perception.

The National Highway Traffic Safety Administration (NHTSA) completed a study to document the problems experienced by older drivers in these driving situations, and to determine if the difficulties can be predicted from measures of functional capability. The report, Intersection Negotiation Problems of Older Drivers, is available now.

MultiCAD Measures Functional Abilities

The Scientex Corporation developed the Multiple Competency Assessment for Driving (MultiCAD) test battery, which is a PC-based system of nondriving tests used to measure skills thought to be critical to safe driving. These include a number of acuity, contrast and motion sensitivity, and useful field of view tests. It has an accelerator and brake pedal assembly to measure brake reaction and stop-and-go decisions on a video driving test.

Field Study

Next, the researchers conducted field observations of 82 older drivers referred to the California Department of Motor Vehicles (DMV) for special testing, ranging in age from 61 to 92. The median age was 78. Of the 82 drivers, the referral source labeled 26 as cognitively impaired, and 56 as cognitively unimpaired.

Each driver first completed the MultiCAD battery of functional status tests to measure vision, attention, and selected perceptual skills. Then, they performed test drives over a common standard route of relatively low familiarity. Unless terminated for safety reasons, the driver then completed a test drive over a highly familiar route in his or her home area. On both routes, the drivers drove their own vehicles, accompanied by a DMV examiner. Driving errors were recorded by in-vehicle cameras installed on the vehicle by the project team, and by the DMV examiner.

Common Errors Of Older Drivers
At Intersections

Scanning errors were extremely common, as measured by the video camera. Drivers failed to observe behind their vehicles before slowing down during the approach to an intersection 87 percent of the time on unfamiliar routes and 96 percent of the time on familiar routes. These percentages calculate how often an error occurred in relation to the total number of opportunities to make the error.

Older drivers also failed to scan to the sides after entering the intersection 75 percent of the time on both route types. One type of maneuvering error, infringing on others' right of way when changing lanes, occurred at a 90 percent rate on unfamiliar routes and 57 percent rate on familiar routes.

The study documented whether the errors occurred with any particular type of traffic control (signal, stop sign, yield, or no control), the familiarity of the course, and the type of movement the driver was making (going straight through, or turning left or right). The error rates at signalized intersections were relatively constant regardless of how familiar the driver was with the route. The error rates were lower, however, on the familiar course for right turns at intersections that had yield signs or were uncontrolled. This may have resulted from drivers knowing what to look for as a result of experience in familiar areas.

The DMV examiners' scores followed the same general pattern of errors as the video data. Scanning errors predominated across both familiar and unfamiliar test routes, and maneuver errors occurred less frequently. Among the more common maneuver errors, stopping for no reason was noted on 39% and turning too wide or too short on 46% of test drives over unfamiliar routes. On familiar routes, both of these errors dropped to 26% of test drives.

Relating Functional Status To Driving Errors

Some of the functional status tests predicted driving performance. Each test score was correlated with an error score derived from the DMV examiner's scores during the road test. Since some driving errors were more serious than others, they were weighted to reflect this.

Two items significantly predicted a driver's error test score. The first was the speed of correct responses on certain measures of visual acuity and contrast sensitivity. The second was brake response accuracy (or error rate) when a pedestrian or vehicle in the driving video constituted a safety threat.

Older drivers, like all drivers, seem to engage in many intersection negotiation behaviors that could be classified as driving errors, but which have little apparent bearing on safety. The report discusses the types of errors that best predict crashes and that are consistent with the practices of licensing examiners. It is important to distinguish between measures that do not affect crashes. The difficulty remains in identifying who the high risk older drivers are. Poor results on component measures of driving ability may mask overall competence for the driving task, especially among older drivers who apply compensatory strategies.

How To Order

The Intersection Negotiation Problems of Older Drivers report is in two volumes: Volume I: Final Technical Report (56 pgs) and Volume II: Background Synthesis on Age and Intersection Driving Difficulties (133 pgs). For a copy, write to the Office of Research and Traffic Records, NHTSA, NTS-31, 400 Seventh Street, S.W., Washington, DC 20590, or send a fax to (202) 366-7096. Alan Block was the contract manager of this project, email: ablock@nhtsa.dot.gov

U.S. Department
of Transportation
National Highway
Traffic Safety
Administration
400 Seventh Street, S.W. NTS-31
Washington, DC 20590

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If you would like to receive a copy contact:
Linda Cosgrove, Ph.D., Editor, Evaluation Staff
Traffic Safety Programs
(202) 366-2759, fax (202) 366-7096
mailto:lcosgrove@nhtsa.dot.gov