Driver Behavior During Visual-Manual Secondary Task Performance: Occlusion Method Versus Simulated Driving

An experiment was conducted to assess proposed acceptance criteria of the National Highway Traffic Safety Administration's (NHTSA’s) Visual-Manual Driver Distraction Guidelines. Seventy-two participants, ages 18-75 (3 age groups, balanced gender), performed secondary tasks (radio tuning, destination entry, 7-digit phone dialing, and 10-digit phone dialing) in two protocols: (1) driving a low-fidelity simulator; and (2) wearing occlusion goggles. Secondary tasks were performed using the integrated in-vehicle information and communication system of a 2010 Toyota Prius V. The Dynamic Following and Detection (DFD) driving simulator protocol combines car following with detection of visual targets presented in the roadway display during a single 3-minute drive. Performance metrics included: total eyes-off-road time (TEORT), mean glance duration, proportion of long glances, standard deviation of lane position (SDLP), car following delay, target detection accuracy (proportion correct), and target detection response time. The occlusion protocol required participants to perform 5 instances of each secondary task while wearing occlusion goggles that switched every 1.5 seconds between open and closed (occluded) states (as defined in ISO 16673). Total shutter open time (TSOT) was the performance metric. The full sample (N = 72) was used to determine “ground truth” test outcomes for each metric. Test results were compared with expectations that radio tuning is acceptable for driving and destination entry is not. Occlusion TSOT values were greater than the 9-second proposed NHTSA acceptance criterion, indicating all four secondary tasks did not meet the acceptance criterion. TEORT values were less than the 12-second proposed NHTSA acceptance criterion for 7-digit dialing and radio tuning, but not for destination entry and 10-digit dialing. Criterion values for mean glance duration and proportion of long glances were not sensitive to differences among secondary tasks. The observed TEORT/TSOT ratio was close to 1.0, considerably less than the predicted value (1.33). DFD driving performance metrics were compared to fixed and benchmark acceptance criteria. Results for fixed criteria included: 1) car following delay – all tasks met acceptance criterion; 2) SDLP – destination entry did not meet acceptance criterion, other tasks met criterion; 3) target detection response time – all tasks met acceptance criterion; and 4) target detection accuracy – destination entry did not meet acceptance criterion, other tasks met criterion. Results relative to the destination entry benchmark included: 1) car following delay – no tasks met acceptance criterion; 2) SDLP – all tasks met acceptance criterion; 3) target detection response time –acceptable for 10-digit dialing, but unacceptable for other tasks; and 4) target detection accuracy – all tasks met acceptance criterion. Results were not entirely consistent for fixed vs. benchmark approaches. Analyses of 3 subsets (N = 24) were performed to assess consistency of results over repeated testing. Results were consistent across groups for the glance-based metrics in both the DFD and occlusion protocols, however because criteria for some metrics did not discriminate among tasks as predicted, these tests were not strong. Results for several driving performance metrics were not consistent across groups. Strong age effects were apparent for all metrics. Younger drivers (18-25) were most likely to provide outcomes meeting the acceptance criteria; older drivers (60-75) were most likely to provide outcomes not meeting the acceptance criteria. Strong and consistent age effects reflect heterogeneity of sample construction, which could reduce test sensitivity when using relatively small samples. Overall, 3 metrics found destination entry unacceptable and radio tuning acceptable: (1) TEORT (driving simulator); (2) lane position variability (SDLP); and (3) target detection accuracy. The distribution of TSOT values suggests that increasing the proposed criterion could provide the expected outcomes. The proportion of long glances appears more promising than mean glance duration for ensuring tasks can be performed without long glances. Samples of 24 cannot be expected to provide consistent results over repeated testing for all metrics. Both occlusion and DFD protocols are too demanding for some older drivers. Other procedural issues that could influence test outcome were identified.