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

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

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: km/h –High congestion: km/h Variance in estimated speed: –Low congestion: (SD = 16.63) –High congestion: (SD = 32.19)

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