Traffic and Ratings of Driver Workload: The Effect of the Number of Vehicles and Their Distance Headways

This experiment examined how variations in traffic affected driver workload. Some 24 subjects, 12 younger, 12 older, drove a driving simulator. There were eight scenarios that involved a lead vehicle, a following vehicle, and up to two vehicles in an adjacent lane, one ahead, one behind. Depending on the condition, the subject rated the workload of driving or the visual scene was periodically occluded (visible for 0.5 s after each button press). Ratings were obtained by showing looped clips of expressway scenes (anchors) below the center channel of the simulator. This paper only discusses the rating data, which were extremely stable and seemingly unaffected by age. The workload increased when distance headway (DHW) decreased. In terms of effect on workload, from greatest to least, they were: lead vehicle, vehicle in adjacent lane – ahead, vehicle in adjacent lane – behind, follow vehicle in the same lane.