Alvah C. Bittner

Comparison of four subjective workload rating scales

Four subjective workload scales were compared along four dimensions: sensitivity, operator acceptance, resource requirements, and special procedures. The scales were the Modified Cooper-Harper scale, the National Aeronautics and Space Administration Task Load Index (TLX), the Overall Workload (OW) scale, and the Subjective Workload Assessment Technique. Three U.S. Army systems were studied for potential workload concerns. Data from five different studies on the three systems were compared along the aforementioned four dimensions. Results indicate that all four scales are acceptable tools and are sensitive to different levels of workload. However, TLX and OW are consistently superior when considering sensitivity, as measured by factor validity, and operator acceptance. This research is an example of a systematic approach for examining human factors measurement tools.

On-road versus simulator data in driver model development: Driver performance model experience

Driver Performance Model (DPM) development has provided results reflecting on the debate between on-road and driving-simulator data in driving research. Developed for FHWA, DPM is a computational micro-process model of driver behavior that has been designed to simulate—in detail—the driver’s perceptual, cognitive, and control processes to generate steering, braking, and acceleration inputs to the vehicle. The requirement to develop driver data for prediction of absolute on-road performance—versus typical interest in ordinal findings to be later validated via on-road studies—led to the collection of comparable on-road and simulator data and their subsequent comparison. Comparisons of corresponding curve-entry speeds and speed profiles revealed a profound divergence between the on-road and simulator results (t = 9.39, p < .005). Compared with simulator drivers, on-road drivers tended to have higher curve-entry speeds for the more difficult (sharper) curves and lower speeds for the less difficult curves. This trend, though reduced in magnitude, was apparent even after statistical adjustments for differences in respective tangent speeds (t = 2.67, p < .01). These results are discussed in light of emerging on-road and simulator capabilities. The discussion and earlier results altogether supported two conclusions: (a) debate concerning on-road versus simulator research studies is likely to continue with their rapidly emerging individual capabilities, and (b) on-road research currently provides the best basis for driver model development where one-to-one real-world predictions are required (e.g., DPM).

Brake pulsing as haptic warning for an Intersection collision Avoidance countermeasure

Human factors issues involved in defining driver warnings for potentially hazardous situations at intersections are addressed. General issues include what information to present to drivers (warning content), when to present it (timing of warning), and how to present it (type of warning modality). The work reported is being conducted to assist in the design of a driver-vehicle interface (DVI) warning system for the Intersection Collision Avoidance Using Intelligent Vehicle Highway System Countermeasures (ICA) program. The ICA program is one of four collision avoidance system programs sponsored by the NHTSA Office of Crash Avoidance Research. Initially, the results of an on-road baseline study that examined driver behavior during approaches to intersections controlled by stop signs are reviewed with respect to the timing of driver warnings. Subsequently, haptic warning characteristics for an intersection collision avoidance system are defined, and DVI design guideline recommendations for implementing haptic warnings generated through vehicle brake pulsing are included. Vehicle brake system modifications required to achieve brake-pulsing parameters are described. Human factors test plans directed toward verification that physical properties generated through brake pulsing are readily recognized and accepted by drivers are delineated. As part of verification efforts, track tests will be performed with various intersection approach speeds and driving maneuvers. Effect of velocity on perception of haptic warning will be evaluated for ranges of magnitudes and duration of brake pulsing. The test results will support ICA test-bed development in the latter part of the ICA program.

Generic Workload Ratings of a Mobile Air Defense System (LOS-F-H)

Operator workload (OWL) scales were used to obtain ratings of generic mission scenarios and tasks for a mobile air defense missile system (LOS-F-H) following a candidate-selection field evaluation. NASA TLX, SWAT, Overall Workload (OW), and the Modified Cooper-Harper (MCH) ratings were obtained from both crew and Subject Matter Experts (SMEs). Jackknife factor analysis revealed the presence of only a single “OWL” factor for both crew and SMEs (explaining 75.9% and 82.6% of the respective total variances) and indicated a significant (p < 0.00005) ordering of the mean factor loadings: TLX (0.924) was significantly greater than OW (0.905) and MCH (0.904), which were greater than SWAT (0.778). Subsequent analysis of OWL factor scores indicated that the crew and SMEs yielded essentially equivalent evaluations of OWL for the system variables investigated. This analysis also indicated that the highest levels of OWL were obtained for the track-to-intercept task during dual Rotary-Wing (RW) and Fixed-Wing (FW) attacks, although the ID/IFF task during a dual RW attack was almost as high. These findings are discussed in the context of a methodology for assessing OWL.

Computational Techniques Used in the Driver Performance Model of the Interactive Highway Safety Design Model

The Interactive Highway Safety Design Model (IHSDM) is a high-priority research area for FHWA. IHSDM is a software system for evaluating the safety of alternative highway designs in a computer-aided design environment. The initial phase of this research program is to develop IHSDM for use in the design of two-lane rural highways. IHSDM includes a driver-vehicle module that simulates the moment-to-moment actions of a single driver-vehicle unit. Reviewed are the computational approaches that have guided the implementation of the driver performance model (DPM) that along with a vehicle model and other components constitute the driver-vehicle module. Five major computational functions of DPM are reviewed: perception, speed decision, path decision, speed control, and path control. Comparison of model results with data from a driving simulator demonstrates the ability of DPM to account for the horizontal curve deflection angle on the speed profile.

Operator Workload for Military System Acquisition

The purpose of this paper is threefold. Initially, we take the liberty of introducing the subject of workload: what it means and why we as engineers and behavioral scientists are interested in it. We assume that practically all engineers involved in the design of new weapon systems are, by now, at least aware of the importance of operator workload (OWL). Indeed, the widely endorsed, yet poorly addressed, initiative to reduce operator workload is partly responsible for the seemingly mad rush to provide ever greater levels of automation in the cockpit, at the helm, or at the workstation. Those of us who practice the Human Factors Engineering profession realize the folly of providing automation simply because it is technologically feasible .. but that philosophical argument must remain the subject for another day. In any event, a brief discussion of workload is necessary to set the stage. The second purpose of this paper is to identify specific workload prediction and assessment models which we have reviewed in our research program, and present summary opinions as to the utility of these techniques. Lastly, we will suggest some top level. questions, strategies, and issues which we all must confront when the time comes to actually select and apply a technique.

MODIFICATION AND PARTIAL VALIDATION OF THE DRIVER/VEHICLE MODULE

Four assumptions of the Driver/Vehicle Module of the Interactive Highway Safety Design Model were tested against data obtained in two on-road studies of driver behavior. Supported were assumptions that drivers track to the inside of horizontal curves and that a linear control model is adequate for describing steering behavior. Not supported were assumptions of consistent preferred lateral acceleration in horizontal curves and consistent preferred longitudinal accelerations and decelerations during curve approach and exit. Experimental results support (a) an analytically derived square-root relationship between preferred lateral acceleration and curvature and (b) an analytically derived square-root relationship between longitudinal acceleration or deceleration and total speed change.

Operator Workload in the UH-60A Black Hawk: Crew Results vs. Tawl Model Predictions

An empirical study was undertaken to collect real-time workload estimates of pilots and copilots performing a resupply mission in a UH-60A flight simulator. Overall and peak workload (OW and PW) ratings were collected for twelve mission segments. These ratings were compared with OW and PW values predicted by the Task Analysis/Workload (TAWL) simulation model. High correlations were found between TAWL-based predictions and crew results for OW (r = 0.82 to 0.95; p < .01). Lower correlations were found for PW (r = 0.62; p < .05).

Analytic Techniques for the Assessment of Operator Workload

Workload techniques may be divided into two broad classes: 1) Analytic techniques — predictive techniques that may be applied early in system design before “operator-in-the-loop” studies; and 2) Empirical techniques — workload measurements taken with “operator-in-the-loop” during simulator, prototype, or system evaluations. Described here are five categories of the analytic techniques: 1) Comparability Analysis; 2) Mathematical Models; 3) Expert Opinion; 4) Task Analytic Methods; and 5) Simulation Models. A description, with examples, is given for each category. The motivation for focusing on the analytic techniques lies in their application during the earliest stages of system development where the greatest design flexibility is available at the least cost.

IDENTIFICATION OF DESIRED SYSTEM FEATURES IN AN ADVANCED TRAVELER INFORMATION SYSTEM

This study evaluated consumer acceptance of variations of a currently available Advanced Traveler Information System (ATIS). We also wanted to determine if video demonstration was sufficient for observers to grasp the fundamentals of ATIS devices. A total of 109 licensed drivers viewed two videotaped demonstrations of TravTek, and then completed questionnaires. Principal Factor Analyses resulted in patterns of desired features and other composite variables used in regression analyses. Basic map features (e.g., vehicle position/location, outline of route) and voice features were the two dominant feature patterns. Other composite variables included understanding of the system capabilities, trust, self-confidence, tolerance of system errors, demonstration fidelity and attention. Results of the regression analyses indicated that different variables were significant predictors of each pattern of desired features.