Safe Mobility for Older Drivers

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II.E. ON-ROAD MEASURES OF SAFE DRIVING PERFORMANCE

1. California Modified Driving Performance Evaluation (MDPE)

2. California Area Driving Performance Evaluation (ADPE)

3. Washington University Road Test (WURT)

ON-ROAD PERFORMANCE MEASURES OF DRIVING SAFETY

California Modified Driving Performance Evaluation (MDPE)

* 75 "referred" subjects aged 60-91 (26 of which were identified as probably being cognitively impaired to some degree). The drivers were referred to the DMV for reexamination due to a medical condition (by physician, optometrist, ophthalmologist), a series of licensing test failures, a flagrant driving error (police referral), or some other indicator of driving impairment.

* 31 paid "volunteers" aged 56-85, recruited through signs posted at study site or word of mouth.

Based on the California Driving Performance Evaluation (DPE), this driving test measures the constructs of visual search, speed control, and directional control, and it features a fixed number of possible errors, objective scoring criteria, and the scoring of elements of specific (Astructured=) maneuvers at specific locations.

Examples of structured maneuver errors are "inadequate traffic check," "poor lane position," and "turns too wide or too short."

A subset of errors defined as critical driving errors were listed in a separate section of the DMV score sheet. These are serious errors; under normal testing circumstances (i.e., other than a research situation), a driver=s test would immediately be terminated. Critical errors included: examiner intervention; driver strikes object; drives up/over curb/sidewalk; drives in oncoming traffic lane; disobeys sign/signal; dangerous maneuver; inappropriate reaction to school bus; inappropriate reaction to emergency vehicle; inappropriate speed; inappropriate auxiliary equipment use; turn from improper lane.

A subset of critical errors was also defined as hazardous errors, with the belief that these errors are predictive of driving impairment. These included "dangerous maneuver" and "examiner intervention."

A weighted error score serving as the primary criterion (dependent) variable for these analyses was calculated by adding the total number of errors (regardless of severity) to twice the sum of critical and hazardous errors. Since hazardous errors are a subset of critical errors, and critical errors are a subset of total errors, this scheme weighted hazardous errors by a factor of five and other critical errors by a factor of three.

Confusion (concentration) errors were also recorded, when a subject was unable to proceed to field office at end of test, or drove past the street on which the field office was located and did not recognize their error.

Test times ranged from 30 to 45 min.

The MDPE was conducted along a fixed route near the Santa Teresa office of the DMV.

There were significant correlations between the following driving measures and group--referral vs volunteer:

unweighted errors (.460); weighted errors (.470); hazardous errors (.388); critical errors (.386); and confusion errors (.418). Test failure was not significantly correlated with group.

The following variables were also significantly correlated with age:

unweighted errors (.395); weighted errors (.409); and critical errors (.355).

There were no significant differences between cognitively impaired referrals and cognitively nonimpaired referrals on total errors, critical errors, or hazardous errors.

Cognitively impaired referrals had significantly more "confusion errors" than cognitively nonimpaired referrals. This particular MDPE measure was the only driving performance measure where there was a difference in driving performance between cognitively impaired and cognitively nonimpaired drivers.

Janke & Eberhard (1998)

see also :

Staplin, Gish, Decina, Lococo, and McKnight (in press)

ON-ROAD PERFORMANCE MEASURES OF DRIVING SAFETY

Washington University Road Test (WURT)

Participants recruited from Alzheimer's Disease Research Center (ADRC) at Wash. Univ. School of Medicine

*58 healthy elderly control subjects, mean age = 76.8; Clinical Dementia Rating =0

*65 subjects with Dementia of the Alzheimer=s type (DAT), mean age = 73.7; Divided into 2 groups: 36 Ss with Clinical Dementia Rating = 0.5 (very mild DAT) and 29 Ss with CDR = 1.0 (mild DAT).

All S=s had corrected acuity of at least 20/50

Short Blessed Test scores (mean and sd) for CDR 0, CDR 0.5, and CDR 1.0 were 1.4 + 2.1, 4.8 + 5.9, and 14.2 + 6.7, respectively. Scores for this test range from 0 (no impairment) to 28 (maximal impairment). A univariate ANOVA indicated a significant difference across CDR groups on the Short Blessed Test.

NOTE: no analyses were reported in this article regarding the relationship between performance on the Short Blessed Test and driving performance; however, LH provided the following stats: correlation between global rating on WURT and Short Blessed test perf. was signif. (r=-0.56, p<0.0001). Mean and sd SBT: Safe: mean =3.4, s.d.= 5.1

Marginal: mean =5.1 s.d.=5.7

Unsafe: mean=12.3* s.d.=9.1

* p<0.0001

Objective: To assess the reliability and stability of a standardized road test for healthy aging people and those with dementia of the Alzheimer type (DAT).

*The WURT is a 9.6-km course with urban 2-, 4-, and 6-lane streets providing various road and traffic conditions to enable detection of driving behaviors associated with crashes in the elderly: failing to yield right-of way, responding inappropriately to traffic signs and signals, and difficulty negotiating intersections.

*The initial test site (a large empty asphalt parking lot) was used for familiarization of the subject with the test vehicle (standard-model car with automatic transmission, and dual brake pedals). Seven basic motor vehicle operational tasks were assessed on pass/fail basis: insert key into ignition; start engine; shift from park to drive; drive forward 45 m, make a left turn; stop. Ss proceeded from closed course to open segment, unless major safety concerns were detected during familiarization. A commercial driving instructor plus the Principal Investigator accompanied each S during the drive. A global "safe/behavior unlikely to result in crash," "marginal/small-to-moderate risk of crash," or "unsafe/substantial risk of crash" subjective rating of driving performance was made by the instructor & PI.

*A quantitative score was also calculated independently by instructor and PI. The best possible score was 108, the worst possible score was 0. A 3-point scale (0=moderate to severe impairment; 1=mild impairment; 2=no impairment) was used at predetermined locations on the following maneuvers: left turns, stops, lane maintenance, speed, traffic awareness, merging, concentration, lane changes, traffic signs, comprehension of directions, attention to task, awareness of how driving is affecting others, judgment, need for intervention by instructor for safety reasons.

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FINDINGS (Cont=d)

For specific driving beh., 24 (81%) of the unsafe drivers required assistance [vs 11 (14%) of the safe drivers}. Turn signal use/non use did not discriminate between safe & unsafe drivers. Strongest correlation with the global rating was with qual. judgments on WURT driving perf. These judgments evolved from observing the overall cognitive performance of the subject=s driving.

Washington University School of Medicine

Urban medical school and urban highways and streets

*There was a significant relationship between global rating and CDR, such that most CDR 0 Ss were rated as "safe" 78% (45/58) compared to 67% (24/36) of CDR 0.5 Ss and 41% (12/29) of CDR 1s. Only 3% of CDR 0 Ss were judged "unsafe," but 19% of CDR 0.5 and 41% of CDR 1s were judged "unsafe"" The remaining Ss in each CDR group were rated "marginal."

*As dementia severity increased, the quantitative scores decreased. Mean road test scores for the CDR 0, CDR 0.5, and CDR 1 groups were 94.3, 92.0, and 85.6. Correlational analyses showed a significant association between drive performance scores and CDR level.

*The quantitative score from the PI and the global rating from the driving instructor were highly correlated, such that safer global ratings were associated with higher quantitative road test scores. Interrater reliability for the driving instructor and PI for the global rating was also high.

*Stability of driving behavior over time was examined with a 1-month test-retest paradigm for 63 subjects. The stability of the global rating by the same driving instructor on the same course was 0.53, and for the quantitative score, reliability was 0.76. Few safe drivers at baseline became unsafe at 1 month, and few unsafe drivers at baseline became safe at 1 month. The disproportionate instability came from the Amarginal= drivers. It was suggested that visual environmental cuing (e.g., following preceding vehicle) may affect driving performance; cognitively impaired drivers may seek the actions of other drivers to follow the flow of traffic.

Hunt, Murphy, Carr, Duchek, Buckles, and Morris (1997a, and 1997b)