A Measurement Systems Analysis of Total Shutter Open Time (TSOT) as a Distraction Metric for Visual-Manual Tasks

Abstract

The Total Shutter Open Time (TSOT) metric was examined for estimating the visual-manual distraction potential of in-vehicle devices. A measurement systems analysis was carried out on TSOT using data on thirteen visual-manual tasks from the CAMP Driver Workload Metrics Project. TSOT showed low test-retest reliability but high repeatability when data were averaged across persons by task. TSOT predicted task completion time, lane keeping, speed variation, total glance time, and number of glances away from the road while driving. Tasks were classified into higher and lower workload categories based on literature, analytical modeling, and engineering judgment. TSOT showed a high percentage of statistically significant pairwise differences between higher vs. lower workload tasks. Different classification rules were also applied to TSOT. The best rule to classify tasks as higher or lower workload consistent with prior prediction was one in which a mean TSOT > 7.5 seconds implied the task was of higher workload. These results illustrate a general procedure to assess driver workload measures in general and the usefulness of TSOT in particular.