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A class of driver attentional workload metrics has been developed for possible application to the measuring and monitoring of attentional workload and level of distraction in actual driving, as well as in the evaluation and comparison of in-vehicle human machine interface (HMI or DVI) devices. The metrics include driver/vehicle response and performance measures, driver control activity, and driver control models and parameters. They are the result of a multidisciplinary, experimental and analytical effort, applying control theory, manual control, and human factors principles and practices. Driving simulator and over-the-road experiments were used to develop, confirm, and demonstrate the use of the metrics in distracted driving situations. The visual-manual secondary tasks used in the study included navigation destination entry, radio tuning, critical tracking task, and a generic touch screen entry task.

Typically, driver interactions with in-vehicle devices such as navigation systems have been accomplished using a visual-manual interface. As a result of recent advances in technology, voice activated interfaces are being introduced, which reduce or eliminate the need for manual inputs and related visual scanning. This paper compares driver use of contemporary examples of the 2 different types of interface for several types of navigation destination entry tasks based on over-the-road evaluations. These data include glance behavior, HMI interactions (manual inputs, etc.), driver/vehicle response and performance including lane deviations, and subjective ratings. In general, the results show that, for a given task, the example contemporary voice activated systems result in fewer glances, shorter glance durations, fewer entry steps, improved driver/vehicle performance, and improved subjective ratings for ease of task accomplishment and mental workload.

A study of the effect on driver behavior and performance of varying occlusion parameters and secondary task duration was accomplished using the Dynamic Research, Inc. (DRI) Driving Simulator. Driver glance behavior and performance under comparable primary and secondary task conditions that were driver paced (no occlusion) were studied also. Both occlusion goggles and screen blanking means to interrupt vision were investigated. The several experimental phases included baseline primary driving task only, baseline secondary task only (no occlusion), secondary task with occlusion or screen blanking, primary driving task with goggles occlusion, and primary and secondary tasks combined, driver paced, with no occlusion or screen blanking. The secondary task human-machine interface (HMI) was a generic alpha entry task using a touch screen, located high in the center console.

An over-the-road study of driver destination entry using an example in-dash GPS-based navigation system was accomplished in traffic on urban surface streets and freeways. The evaluation used typical drivers, and a vehicle instrumented to record driver control inputs, vehicle response motions including lateral lane position, and driver eye glances and fixations. The primary task was to follow the routes in a safe manner, while moving with traffic and maintaining speed and lateral lane position. As a secondary task, the drivers entered the successive destinations while driving, using a touch screen, and at their own pace. They were told there was no hurry, nor was there a need to enter the destination quickly. Results are shown for number of keystrokes, total fixation times, number of fixations on the device, fixation duration, lane keeping performance, and subjective ratings related to ease of destination entry.

A simulator intended for driver/vehicle applied research and driver behavior studies is described. Designed and developed by Dynamic Research, Inc. in Torrance, CA, it features a 180 deg forward field of view, an animated graphics roadway scene, modular vehicle dynamics models, instrumented cabs with steering control loaders and aural cueing, an electrohydraulic hexapod motion base with ±2 ft of stroke in each leg, and system operation and data acquisition functions. Automobile and motorcycle cabs are available. Studies to date have considered steering and pedal controls layout, high speed brake in turn, and driver workload related to the use of an in-dash navigation and route guidance system.

The characteristics, functionality, limitations, and applications of mid-level driving simulators are reviewed and discussed. For this paper a mid-level simulator is defined as one which has a large roadway scene display typically comprising animated computer graphics, it may have a motion system or be fixed base, it should have a dedicated cab with a steering feel system and interactive controls and displays, it has a parametrically configurable vehicle dynamics model, data acquisition is provided for, and the simulator is intended to be used for driver behavior research and vehicle or highway research and development studies. Possible simulator sickness issues are discussed, and categories of mid-level driving simulator applications are noted. Approximately 20 different contemporary driving simulators are included in the survey.

Results of a study to analyze and correlate handling-related driver/vehicle system response and performance data are reported. Steering control tasks involving maneuvers and disturbance regulation are emphasized. Correlations between vehicle handling parameters, objective measures, and subjective rating data have been made. These have lead to the tentative definition of values of steering gain and effective yaw time constant which are preferred for satisfactory handling qualities and performance for passenger automobiles.

Models have been developed to describe the dynamic response and performance of drivers, vehicles, and driver-vehicle systems; and recent experiments have provided some quantification and refinement. This paper summarizes the theory and the data, and attempts to provide part of the transition between properties of the human and the assessment of safety performance in driving. The model and data shown emphasize steering or directional control situations. Simulation experiments with random crosswind gust disturbances were used to measure driver-vehicle describing functions for a number of driver subjects and experimental replications. The results are consistent with previous data and show good repeatability within subjects on successive runs. Interpretation of the data in terms of the driver-vehicle model indicates that the driver's outputs can be explained in simplest terms as functions of lateral position and heading.

Driver response and performance can be quantified by observing the stimulus-response environment. Yet the driver's inherent adaptability allows him to have seemingly adequate performance in potentially hazardous driving situations even though he may be operating near the acceptable safety limits. Physiological measures of the driver's internal state can provide further quantification of his performance level and can give a measure of his workload or safety performance margin. Measures of driver physiological and control responses have been made under gust disturbance conditions with the subject's car operating at various speeds. The experimental techniques and data are described, and correlations between the situational parameters and driver stress and control response are shown.