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Publication Number: FHWA-RD-95-176
Date: November 1996
Development of Human Factors Guidelines for Advanced Traveler Information Systems and Commercial Vehicle Operations: Task Analysis of ATIS/CVO Functions
CHAPTER 4. TASK ANALYSIS RESULTS
Analysis of Bridging Tasks
Tasks that serve as an information or procedural "bridge" between two or more functions are the second type of tasks analyzed. An understanding of such tasks is necessary because they bring together the various systems of ATIS into an integrated and functional whole.
Function of Bridging Tasks
Tasks that serve as a bridge between two or more functions provide the procedural link that integrates the output of one function with the input requirements of another. Bridge tasks include those that provide information from one function to another. They also include those that initiate or set up tasks in functions other than the ones found in the initial setup tasks. Examples of bridging tasks include:
Most bridging tasks are preceded by a decision task. The outcome of the decision task may be based on one of two basic conditions. The ATIS has provided the driver with a satisfactory destination or route as part of the planning function. For example, the system has been asked to plan a route from the present location to the nearest hardware store, and a route is suggested that the driver considers suitable. If either the environmental or other conditions surrounding the route have changed, the driver may initiate a change in ATIS functions. For instance, if a driver were preceding on a route to a restaurant and suddenly realized that she needed to get some money at an Automated Teller Machine (ATM), she would initiate a change in functions to locate the nearest ATM along the proposed route.
In general, bridging tasks perform four different functions. These functions are summarized in table 18.
Table 18. Function and description of bridging tasks.
General Characteristics of Bridging Tasks
Of the 165 driver and dispatch–centered tasks examined in detail, approximately 18 percent involved actions that either shifted information from one system to another or from one function to another within a single system.
The most common ATIS bridging task is probably found in the link between planning functions and execution functions associated with IRANS and IMSIS (see figure 15). Such a task is likely to require little more than a single control action indicating acceptance of the system recommendations and simultaneous approval to begin the guidance phase of the trip. In some cases, such as when planning is done in advance of the trip, the bridging task might involve only indicating that the driver is prepared to begin the trip. Since the bridging task itself is relatively simple, there is no real reason that it could not be accomplished safely while the vehicle was moving under most conditions. The most often used ATIS bridging tasks (i.e., those that bridge planning and execution functions as well as planning and destination coordination functions) present few problems to adequate task performance. In the integrated system assumed by this analysis, performing such a task would be, for all practical purposes, a transparent activity in the operation of the system.
A second potential use of ATIS bridging tasks is likely to be when coordinating destination requirements such as reservations at a restaurant, motel, or warehouse loading dock (see figure 16; also see appendix D, Scenarios P6 OSD, P16 OSD, and P20 OSD). Such coordination is likely to be a secondary function of the ATIS and one not likely to involve the driver beyond indicating that reservations are desired and acknowledging that they have been made. This type of task could be accomplished either immediately after confirmation of the plan or destination selection or, if desired, at some later time. Of course, if confirmation of the availability of space is important to the selection of a particular destination, this task would need to be done before initiating route guidance to the destination.
A third potential use of ATIS bridging tasks is as a result of recognizing that conditions may require a change in plans or their execution (see figure 17; also see appendix D, Scenarios P14 OSD, P16 OSD, and C12 OSD). This type of bridging task may involve more complex
behavior than the previously discussed tasks. The initiation of new functions as a result of changed conditions often involves making changes in a route while under way or similar activities that are likely to require that the driver either enter new destination or routing parameters or that he or she review suggested route changes generated by the system. It can be anticipated that such tasks may be required while driving and, furthermore, that the circumstances requiring the change (e.g., traffic congestion or hazardous road conditions) will simultaneously increase the need for the driver to concentrate on the driving task. Such task demands undoubtedly will require that the system be designed to minimize the workload exerted on the driver, while at the same time allowing the necessary actions to be performed to initiate the new function.
The last examined use of ATIS bridging tasks involves the execution of a function (see figure 18) that was developed by one part of the system (e.g., dispatch) but was used by another part (e.g., drivers) (see appendix D, Scenarios C12 OSD and C13 OSD). Such a task potentially involves all of the characteristics of human communications, including the inherent limitations on the accuracy of such communications.
Human Factors Design Implications (General and Specific)
Bridging functions are, for the most part, transparent to the driver. However, in most cases, the driver still has to acknowledge his or her acceptance of the system's recommendations. The exact method of doing so will depend on system technical design. Such a design could range from manual switch activation through voice recognition. It might also include passive acceptance or acknowledgment (i.e., performing the first required action).
In most cases, following the driver's acceptance of a specific system's recommendation, the system will automatically initiate the actions. As a consequence, such activities will be transparent to the driver and will not require any specific human factors recommendations.
However, if there is a need for the system to interrogate the driver to his or her next course of actions, these interrogations should satisfy some human factors guidelines. Text presented to the driver should be made up of short sentences, should use standard terminology, and should include one request at a time.
Finally, to minimize the driver's workload, it is essential that these system's requests be limited to a small number of steps. If it becomes impossible to reduce the number of system's requests, such as in a change of plans, the system should prompt the driver with a statement indicating the need to pull over in order to continue the process.
Table 19 summarizes the general characteristics and considerations associated with bridging tasks.