Driving me Crazy: Predicting State Driver Stress in

the Roadway Environment

Christine M. Wickens

York University

The Focus on Driver Anger and Driver Stress

• Causal or correlational relationship

• Limitations of research methodology

Personality and Situational Variables Assessed in the Present Study

• Traffic congestion

• Trait driver stress

• Occupational stress

• Time urgency

• Perceived control

• Gender

Hypotheses

1. State driver stress would be greater in high than in low traffic congestion.

2. Time urgency would lead to greater state driver stress.

3. In low traffic congestion, state driver stress would be greater among high trait stress drivers.

4. In high traffic congestion only, state driver stress would be predicted by the interaction of occupational stress and trait driver stress susceptibility. Specifically, state driver stress would be greater among high trait stress drivers, but exaggerated among those with elevated occupational stress.

Participant Recruiting

• Snowball sampling

• Sought 59, got 42– 6 others eliminated for failing manipulation check– 5 others eliminated for violating participation criteria

• Criteria for Participation:– Travel home from work alone– Along a 400- or similar series highway– Encounter both high and low traffic congestion on highway

during this commute

Measures

• Driving Behaviour Inventory - General (DBI-Gen; Gulian, Matthews, et al., 1989; Hennessy & Wiesenthal, 1997)

• State Driver Stress Questionnaire (SDSQ; Hennessy & Wiesenthal, 1997)

• Job Stress Survey (JSS; Spielberger & Vagg, 1999)

• Demographic and Vehicle Information

Procedures

• Completed DBI-Gen, JSS, and demographic, occupational, and vehicle use survey.

• Identified high and low traffic areas and places to safely park vehicle.

• On evening of the testing session, drove through first traffic area and called experimenter. SDSQ was administered over phone. Procedures repeated for second traffic area.

Evaluation of Hypotheses

1. State driver stress would be greater in high than in low trafficcongestion.

2. Time urgency would lead to greater state driver stress.

3. In low traffic congestion, state driver stress would be greateramong high trait stress drivers.

4. In high traffic congestion only, state driver stress would bepredicted by the interaction of occupational stress and trait

driver stress susceptibility. Specifically, state driver stresswould be greater among high trait stress drivers, butexaggerated among those with elevated occupational stress.

Why No Trait Driver Stress X Job Stress Interaction?

• Methodological Interpretations– Non-significant interaction in the low

congestion condition is a true effect.

State Driver Stress as a Function of Job Stress and Trait Driver Stress

(median split) in Low Traffic

Occupational Stress

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Trait Driver Stress

High

Low

Why No Trait Driver Stress X Job Stress Interaction?

• Methodological Interpretations– Non-significant interaction in the low

congestion condition is a true effect.– Levels of congestion included within each

participant’s high and low congestion conditions respectively were not homogeneous or extreme enough.

Evidence of Problems with Traffic Congestion Levels

• Mean estimated speed:– Low congestion: 103.98 km/h– High congestion: 63.83 km/h

• Variance in estimated speed:– Low congestion: 276.56 (SD = 16.63)– High congestion: 1036.20 (SD = 32.19)

Evidence of Problems with Traffic Congestion Levels (cont’d)

LowCongestion

HighCongestion

Study N Mean SD Mean SD

Current Sample 42 31.17 17.81 37.19 20.50

Hennessy &Wiesenthal (1999a)

60 32.08 17.05 52.48 23.66

Hennessy, Wiesenthal,& Kohn (2000)

58 28.41 15.72 43.08 17.53

Comparison of SDSQ Means and Standard Deviations among Multiple Samples

Understanding the Trait Driver Stress X Job Stress Interaction (cont’d)

• Conceptual Interpretation

- A Curvilinear Relationship– The occurrence of job stress by trait driver

stress interaction effects on state driver stress is curvilinearly related to traffic congestion classified into three levels: low, crowded but moving, and stop and go.

Understanding the Trait Driver Stress X Job Stress Interaction (cont’d)

• Levels of the Curvilinear Relationship– Low Congestion: Minimal cognitive resources required, thus

occupational stressors able to impact on a driver’s perception of the roadway environment.

– Medium (Crowded but moving) Congestion: More attention and focus required for safe operation of the vehicle. This more intense concentration prevents occupational stressors from entering a driver’s immediate consciousness and adding to the immediate experience of driver stress.

– High (Stop-and-go) Congestion: Minimal cognitive resources required, thus occupational stressors able to impact on a driver’s perception of the roadway environment.

Applications and Future Directions

• Education and treatment programs

• Springboard to other research (e.g., effects of driver stress on job stress)