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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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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 2. TASK ANALYSIS PROCEDURE
AN INTEGRATED DESCRIPTION OF DRIVING AND ATIS TASKS
The task analysis presented in this report consists of a hierarchical description of operational sequence diagrams and task characterization tables associated with using an ATIS and with driving. As such, tasks are described in substantial detail. Appendix D consists solely of this description and includes many tables describing individual tasks. While this detailed description of individual driving tasks provides insight into specific ATIS tasks, this representation may not convey how specific tasks or a series of tasks combine with others in a more general description of driving with an ATIS. Therefore, a more simplified description of the driving tasks is needed to summarize the complex and detailed task listing, making the more detailed description understandable. Specifically, a summary of driving and ATIS functions will help to place the detailed description of individual tasks in a meaningful context. Figure 4 summarizes individual tasks as driving functions and provides an index to the task description in appendix D. Each analysis in appendix D is preceded by a similar figure to help identify general sequences of driving functions that might occur in driving scenarios. Since the names of the nodes correspond to functions in the analysis, a sequence of driving functions in figure 4 can quickly be traced to specific tasks.
Figure 4 provides a summary of driving tasks by showing the driving functions that make up the top levels of the hierarchical task description. Each function is composed of subfunctions and tasks that have a common goal embodied by the function. Thus, the network of functions shown in this figure summarize driver activities. The tasks associated with each driving function include tasks specific to driving, such as manipulating the steering wheel. In addition, the driving functions include tasks specific to ATIS, such as entering the desired destination into the route guidance system. Thus, the functions shown in figure 4 summarize and integrate ATIS–specific and driving–specific tasks.
Linking Groups of Tasks
In summarizing the detailed task descriptions with driving functions, figure 5 shows the links between driving functions. These links, drawn as arcs on the figure, reveal sequential dependencies and interactions between functions. Similarly, the arcs connecting driving functions represent triggering conditions that initiate functions and their respective tasks. For example, "vehicle safety verified" designates the arc labeled "A," which connects Inspection with Startup, and shows that Startup occurs only after the vehicle has been inspected and its condition verified. Other functions may require several triggering events to initiate the underlying tasks. For example, Maneuvering depends on Traffic Coordination and Wayfinding. Thus, the arcs serve two purposes. First, they show the sequential dependencies between tasks and functions. Second, the arcs show how changes in system state and information flow link driving functions. These links become particularly useful when examining how drivers act on ATIS information in the context of the other driving tasks because they show how information from an ATIS initiates and changes driver behavior. This becomes particularly important when drivers must coordinate ATIS–recommended actions with environmental constraints, such as traffic conditions and roadway configurations. In general, the driving functions and the arcs that link them provide a summary of the information flows and initiating events that link general driving functions that might be lost in a more detailed view of individual driving tasks.
Integrating ATIS–Specific and Driving–Specific Tasks
The focus of this project is a task analysis of ATIS; however, a meaningful analysis of ATIS must also examine ATIS in the more general context of driving. In particular, an analysis that examines only ATIS–specific tasks would fail to address the critical issue concerning which ATIS functions can be used while driving. Ignoring driving tasks would also fail to address the question of how drivers might assimilate ATIS advice that may help guide their driving maneuvers. The task description, summarized in figure 6, achieves this objective by placing ATIS–specific tasks in the driving context. This is possible because the driving functions shown in this network include both driving–specific and ATIS–specific tasks.
The ATIS–specific tasks were identified by analyzing the potential elements of ATIS. More specifically, a hierarchical task description enumerated tasks associated with each of the functional characteristics identified in Task C. Figure 6 illustrates how ATIS–specific tasks integrate with the driving tasks by annotating the network of driving functions with labels for ATIS functional characteristics. Positioned below each driving function are labels that show which functional characteristics and their associated tasks support each of the driving functions. This places the description of ATIS, developed in Task C, in the context of the more general driving tasks. For example, figure 6 shows that the tasks associated with pre–drive route and destination selection and destination coordination would be associated with the trip planning function. Thus, the labels show how ATIS–specific tasks integrate with the driving functions and the driving–specific tasks. Combining the ATIS–specific tasks associated with the functional characteristics of Task C with the driving–specific tasks provides an integrated description of driving with ATIS.
INTERACTIONS BETWEEN TASKS
The integrated description of driving and ATIS tasks, summarized in the figure preceding each scenario–based task analysis (appendix D), highlights several important interactions that might be ignored by an analysis that focuses solely on individual tasks. These interactions fall into three categories. One category describes how ATIS–specific tasks interact with each other. Another category describes how drivers incorporate information from the ATIS to modify their driving behavior. The third category of interaction addresses how drivers must share their attention with both ATIS–specific and driving–specific tasks.
Interactions Between ATIS–Specific Tasks
Interactions between ATIS–specific tasks are an important consideration because they can lead to unnecessary tasks (i.e., entering data manually that could be transferred from function to function automatically). By examining the information flows and requirements, unnecessary tasks can be eliminated by facilitating the transfer of information through ATIS. Interactions between functional characteristics also are important because combinations of ATIS functional characteristics may overwhelm the driver with information or tasks. Alone, each element of ATIS may provide the driver with information that can easily be assimilated and acted upon. In combination, however, each element of ATIS may contribute to an information flow that could overwhelm the driver. Thus, identifying potential interactions between elements of the ATIS will help to eliminate unnecessary tasks associated with transferring information through the system and avoid overwhelming the driver with information from a large number of disparate sources.
The functional description of ATIS identified information flows that define some of the interactions between elements of ATIS. These interactions were defined in a context that was independent of the driving tasks. However, when seen in the broader driving context, the nature of these interactions may change slightly, and what initially appeared to be seemingly disparate ATIS–specific tasks might now be linked together. For example, although the functional description does not indicate a link between message transfer and route navigation, figure 7 shows how these functional characteristics might interact. Message transfer (6.4) is an ATIS function that needs to be monitored by the driver and, as a consequence, is linked to the driving function Vehicle System Operations and Monitoring. Similarly, route navigation (5.6) is an ATIS function that helps the driver to find a route and, as a consequence, is tied to the driving function Wayfinding. These two ATIS functions could interact together given a particular situation. For example, a driver could be monitoring her vehicle's component and to be informed by the message transfer ATIS function that her appointment with a client is cancelled. She could then use the route navigation ATIS function to alter her route to drive to another appointment.
Thus, in many cases, the tasks of driving may link functional characteristics of ATIS in ways that are different from those based solely on the information flow between functions. Ignoring the links between elements of ATIS that are generated by driving tasks might lead designers to ignore potentially important interactions between functional characteristics. Such interactions need to be considered to minimize unnecessary tasks and limit the potential for driver overload.
Attending to Driving While Attending to ATIS
Besides the interactions of ATIS–specific tasks, the interactions between ATIS–specific tasks and driving–specific tasks are critical in defining a system that a driver can use safely and efficiently. Specifically, examining how drivers may share their attention with the ATIS and the primary task of driving may reveal potential driver overload. If the driver must spend a significant amount of time attending to ATIS–specific tasks, then performance will likely suffer. Thus, a clear description of the driving–specific tasks must parallel the description of ATIS–specific tasks to document the degree that ATIS demands driver attention.
In many cases, ATIS may add tasks that the driver would not otherwise perform while driving. For instance, a driver may select alternate destinations using a data base of local attractions while simultaneously maintaining the position of the vehicle on the road. In other instances, ATIS may augment the driver's capabilities and reduce the number of driving–specific tasks to which the driver must attend. For example, ATIS may eliminate the need to scan the roadside for speed limit signs and then compare the posted speed to the actual vehicle speed. An ATIS could include the posted speed as a marker on the speedometer, directly revealing to the driver any discrepancy between the actual and posted speed. Placing ATIS–specific tasks in the context of figure 4 explicitly demonstrates that the driver must share ATIS–specific tasks with driving–specific tasks. Within this framework, the detailed description of individual tasks documents instances where ATIS increases driver workload with additional tasks and where ATIS may simplify or eliminate some of the driver's tasks.
Integrating ATIS Information and Commands into Driving Behavior
While the issue of sharing the driver's limited attention between driving–specific tasks and ATIS–specific tasks represents a critical issue for the design of ATIS, how the driver integrates ATIS information and commands to guide his or her behavior reveals another important issue. Figure 8 illustrates this general issue through the labeled arcs representing events that initiate driving functions. In general, these initiating events represent driver interpretation of information regarding changes in the position or state of the vehicle relative to the driver's goal. As such, the driver plays an active role filtering, selecting, and interpreting information from the system; the driver does not passively obey the commands of the system. Because the driver plays an active role in processing information from the ATIS, the interaction between driving–specific tasks and ATIS–specific tasks is important. Thus, it becomes important to perform a detailed examination of the factors that a driver must consider when acting on information provided by ATIS. Several factors drive this requirement, including the uncertainty of ATIS–generated information, the need to accommodate traffic dangers when complying with ATIS commands, and the need to coordinate compliance with ATIS commands with roadway constraints and the driver's more general requirements and objectives.
Technological limits associated with map data base accuracy and estimates of future traffic density provide specific examples of two factors that force the driver to evaluate and verify the information provided by ATIS. The arc linking Wayfinding and Maneuvering shows the outcome of this verification process, as does the arc linking Route Modification and Wayfinding. In each of these situations, the driver must evaluate the quality of ATIS information by comparison to external environment. Ideally, the system would provide the driver with information that could easily be integrated with the driver's own perceptions so that the maximum advantage can be gained from both the driver's perceptions and the power of the ATIS. For example, a visual representation of traffic density on an electronic map may provide the driver with an understanding of the traffic patterns that can augment the driver's direct perception of traffic density and experience. In this situation, the driver's knowledge of specific events or contingencies could augment the inherent limits of ATIS. On the other hand, if the system provides only turn–by–turn route guidance (which is generated to accommodate traffic patterns), the driver has no way of detecting instances where the estimate of traffic density provided by ATIS diverges from reality. Figure 8 highlights the need to support the driver in the verification of ATIS information by showing the events and information that link driving functions. If ATIS provides the information depicted on the arcs to augment driving functions, then it is important to support the driver's interpretation of this information to take advantage of the driver's inherent adaptability that ATIS does not possess.
Even if the ATIS provided correct data that did not require the driver's confirmation, drivers could not simply follow the directives of the ATIS; drivers must consider the feasibility of making any maneuver in the context of other vehicles in the immediate area. For example, if an ATIS provides route guidance suggesting a particular turn, the driver must coordinate with other traffic before making a turn. Thus, it is not enough to discuss only the tasks directly associated with ATIS; the tasks associated with evaluating the feasibility of an ATIS directive must also be examined. Similarly, drivers cannot act on ATIS information without considering the constraints of the roadway or the impact on their overall goals. One–way streets, medians, and divided highways represent constraints of the road network that a map data base may not include. Attending to these constraints is part of the routine driving task, and its interaction with ATIS information may have important consequences for how and when the ATIS presents information. The arcs leaving driving functions that draw upon ATIS functional characteristics illustrate the need to coordinate ATIS directives with external events. These arcs highlight the need to consider the interactions between ATIS–specific and driving–specific tasks in coordinating directives provided by ATIS with the more general tasks of driving.
Like roadway constraints, drivers may have a variety of goals and requirements that represent important factors governing their routing and navigation decisions. Without an ATIS, drivers may implicitly attend to these factors when planning and executing a trip. With an ATIS, drivers will need to verify whether ATIS information is consistent with these goals and requirements. For instance, drivers may endeavor to avoid areas they suspect of having high levels of crime. Using an ATIS, drivers will likely use their perceptions of the ability of ATIS to meet these objectives in order to evaluate whether they should act upon the information provided by ATIS. Unlike coordinating ATIS commands with the constraints imposed by other vehicles and roadway geometry, no particular arc or node in figure 8 illustrates the evaluation of ATIS information in the context of driver goals and requirements. Instead, the evaluation may incorporate the results of a series of driving functions, including the dynamic re–evaluation as the driver proceeds along a chosen route. Therefore, some tasks associated with traditional means of navigation and routing may occur in parallel with ATIS–specific tasks. Because drivers may retain and apply pre–ATIS navigation and routing strategies, an understanding of these strategies may ensure that the ATIS provides information consistent with their goals and requirements. Development of such a system requires the relatively detailed description of a broad range of routine driving tasks.
The detailed task analysis presented in this report includes a large number and wide variety of tasks. The analysis describes these tasks in great detail and the resulting description provides a very detailed, but complicated, view of driving with an ATIS. This section and the figure preceding each detailed analysis (see appendix D) summarize and simplify the complex tasks by describing driving in terms of several general functions, which are composed of many individual tasks. The functions and their interconnections provide a summary of the more detailed analysis that highlights interactions, information flows, and triggering events that may be obscured by the more detailed analysis in chapter 4 and in appendix D.
The most important feature of figures 4 through 8 is that they embed a description of ATIS–specific tasks in a description of the more general tasks of driving. Combining ATIS–specific tasks with driving–specific tasks reveals links between elements of an ATIS that emerge when they are considered in the context of routine driving tasks. In addition, figure 8 illustrates several different types of interactions between ATIS–specific tasks and driving–specific tasks. For example, the issue of sharing attention between the primary task of driving and interaction with the ATIS places strict limits on what interactions a driver can have with an ATIS while the vehicle is moving. Likewise, drivers do not respond to information and directives produced by the ATIS in isolation. They interpret, filter, and coordinate this information and the activity it implies with other driving constraints and tasks. Thus, the summary shown in the figure preceding each detailed task analysis in appendix D embeds the task analysis of ATIS within a description of the more general driving tasks. As a result, the figures help to identify issues and design considerations that depend on considering the effects of ATIS in the broad context of how it may affect the general nature of driving.