A principal component analysis of the test track data from the Crash Avoidance Metrics Partnership Driver Workload Metrics project provided evidence for two major components in distraction during driving. The first was related primarily to driver workload, while the second was related to event detection and response. This result confirms previous test track findings. A new finding was that “mean single glance duration” (the average dwell time of the eye on the display or control needed to perform the task), loaded on the second dimension (associated with event detection and response), rather than the first (associated with driver workload). Hence, the duration of single glances to a secondary task is more important for event detection and response when driving than total eyes-off-road time or number of glances. These findings fit with the role of a single off-road glance immediately before a crash being predictive of crash probability. The usual division of “driver distraction” into “visual” and “cognitive” categories is misleading, and “driver distraction” is better subdivided into “workload distraction” and “event-related distraction.”
