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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

 

APPROACH TO THE TASK ANALYSIS

ASSUMPTIONS USED IN THE ANALYSIS

TASK ANALYSIS RESULTS

 

APPROACH TO THE TASK ANALYSIS

Appendices C and D present the detailed task analyses conducted of the ATIS/CVO functions and scenario–based activities. Appendix C provides hierarchical task descriptions for each of the ATIS private and CVO functions. As such, appendix C provides a comprehensive listing of tasks that might confront the driver, organized hierarchically to show which tasks support the various driving and ATIS functions. While appendix C does not provide any information about potential task sequences or decision points, it shows the driver goals associated with each task and how the tasks combine to serve the overall driving and ATIS functions. Appendix D complements appendix C by describing tasks in the context of realistic driving scenarios. This description includes information about task sequences and decision points as well as a more detailed description of each task. Although the task description in appendix D occurs in the context of specific scenarios, the position of each task within the hierarchical task description can be easily identified. Each task in appendix D has a unique number that corresponds to the numbering scheme of the hierarchical task listing in appendix C. The specific content of the scenario–based analyses of appendix D includes:

  • A description of the scenario, its system components, and the major ATIS functions.
  • Graphical depiction of the interaction between the driving and ATIS functions.
  • Graphical depiction of the sequence of task steps involved in performing the scenario.
  • Tables characterizing each task step in terms of task demands and related information.

The summary presented in this section was developed using the detailed task analysis found in appendices C and D. The purpose of this summary is to identify common task requirements among the various situations represented by the scenarios.

In preparing the analysis in appendix D, each scenario was first described in terms of its functional interaction within the pre–drive and drive operational phases of both vehicle and ATIS/CVO use. This provided a link between the earlier function analysis conducted in Task C and the more detailed analysis that follows. It also served the purpose of establishing the scenario functions associated with ATIS/CVO within the larger context of driving.

The functional level description of the scenario is followed by an operational sequence diagram (OSD) of the tasks that would be performed to achieve the goals of the scenario. The OSD provides a graphical description of the relationship between tasks, individuals, or systems that perform each task and the sequence in which the tasks might take place. The OSD provides the primary means for the analysis to evaluate how tasks relate to one another and how task activities might be shared between the user and various systems. Thus, the OSD provides a way for the analyst to evaluate the dynamic qualities of task performance within the scenario.

Accompanying each OSD is a Task Characterization (TC) table containing the detailed task characterization for each task represented by the OSD. The task characterization provides additional information to the analyst, which is of particular importance when evaluating the performance required of an individual when doing that specific task. Figure 9 illustrates the process used to develop this analysis.

 

Results of prior tasks

 

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ASSUMPTIONS USED IN THE ANALYSIS

Advanced Traveler Information Systems (ATIS) are intended to provide a relatively broad range of different services in the context of virtually all possible driving situations. Since the practical environment for ATIS/CVO use is so broad, care must be taken to avoid over–specifying how an individual might use ATIS systems in almost any given situation. Unlike a task analysis of an objective system where it would be possible to identify both the limits of functional use and the way that each function would be carried out, this analysis was done on systems that have not yet been built and lack a fully specified functional allocation. Therefore, the analysis makes assumptions (see table 15) about both functional allocation and task requirements, the extent of which far exceed what would normally be expected of a task analysis.

Table 15. Summary of assumptions used in the task analysis.

ASSUMPTION

SUMMARY

Integrated System

IRANS, IMSIS, ISIS, IVSAWS, and CVO systems are integrated and able to pass information from one to another with minimum human action.

Minimal Use

ATIS functions would only need to be set up by the driver when required for the driving scenario.

Prior Task Completion

Tasks required for system operation prior to those needed for the scenario would have been successfully completed.

Complete Infrastructure Support

ATIS would have all the necessary support to successfully complete the scenario.

Normal System Behavior

All equipment, except as noted in the scenario, including ATIS/CVO functions, would be operating normally.

 

Assumption of an Integrated System

Advanced Traveler Information Systems have been defined as encompassing four distinctly different types of information systems (i.e., IRANS, IMSIS, ISIS, and IVSAWS). Each of these systems could be developed separately and might be purchased and installed by a driver on an optional basis. However, there is sufficient overlap in the functions provided by each of the systems that the use of entirely separate systems would result in redundancy in both display and control of each of the systems. An assumption of entirely independent system functions, presentation, and control would result in both an unrealistic and overly complicated task analysis. For example, such an assumption would require separate entry actions for both destinations requested under the IMSIS and IRANS, an unnecessary and probably unrealistic condition if both systems are in a vehicle. Similarly, completely separate IRANS and ISIS systems would result in route guidance information being presented in addition to cross–street information being provided from ISIS.

Due to the obvious value of having ATIS integrated to share information, suppress redundant information, and minimize the presentation of redundant or unnecessary information, the task analyses of driving scenarios assumed reasonable integration of the ATIS.

Assumption of Minimal Use

Advanced Traveler Information Systems are envisioned to provide functions for a wide range of driver needs. While it would be possible to exercise all or most of the functions in any trip, such use would neither be consistent with driver needs nor a reasonable assessment of the cost/benefit trade–off that using the function would have for a particular scenario. For example, it is probably unrealistic to assume that a driver will initiate the full capabilities of IRANS, including route planning and guidance, when he or she is driving to a familiar location within a local area. It might be equally unrealistic to assume that a driver would tolerate the presentation of all roadway information signs from an ISIS system when driving to work over a familiar route.

Due to the likelihood that drivers will only use systems that they need in a particular circumstance, the task analysis assumes that only those systems needed to perform a set of tasks associated with a particular scenario would be used.

Assumption of Prior Task Completion

The scenarios used in the analysis represent the possibility of creating a list of tasks from the inception of a trip until its completion. Such a representation would have been unnecessarily complicated and lengthy. In addition, such an analysis would have tended to diminish the focus on particular functions as intended by the choice of the scenario. Therefore, the analysis confined itself to a description of the tasks that supported the functions of importance in the scenario and assumed that common preliminary tasks (e.g., turning on equipment and deciding where one wanted to go) were not of central importance to the analysis and thus could be assumed to have been performed.

Assumption of Complete Infrastructure Support

Advanced Traveler Information Systems are going to require a significant amount of infrastructure support. The availability of this support was assumed to be complete in the task analysis. It was further assumed that information necessary to fully support the system function under analysis would be available.

Assumption of Normal System Behavior

Although it is certainly possible to perform a task analysis that includes an analysis of what drivers might do in the event of an ATIS malfunction, doing so significantly complicates the analysis when the specific system design and modes of failure are not yet known. For this task analysis, the assumption was made that the ATIS would have no failures. In the analysis, no failures or related problems were assumed beyond those specified in the scenario.

 

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TASK ANALYSIS RESULTS

Using the results of the task descriptions, as reflected in the Operational Sequence Diagrams (OSDs) and Task Characterization (TC) tables presented in appendix D, task analyses were completed for four different types of tasks:

  • Tasks that are used to set up an ATIS function. (SETUP TASKS)
  • Tasks that serve as bridges between two or more ATIS functions. (BRIDGING TASKS)
  • Tasks that involve decision making by the driver or dispatcher. (DECISION– MAKING TASKS)
  • Tasks that are integrated with critical driving tasks. (DRIVING TASKS)

Each type of task represents specific types of activities that are critical to the proper operation and use of the ATIS and aspects of system use that will need to be considered in the design.

As a consequence, the task analysis results are divided into four main sections, each describing one of the four tasks in greater detail. For each one of the task types, the analysis is subdivided into four parts. First, the Function section provides an operational definition of the type of task involved. The second part, Characteristic, is a description of the general characteristics of the task, including the likely interactions with precursor and successor tasks; but more specifically, it describes the nature of the task in terms of its demands on cognitive and motor processes. Following characterization of the task, the Human Factors Design Implications are discussed, for both general and specific implications. Finally, a summary table presents the main findings described in the previous paragraphs.

Analysis of Setup Tasks

Analysis of Bridging Tasks

Analysis of Decision–Making Tasks

Analysis of Tasks Integrated with Critical Driving Functions

 

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FHWA-RD-95-176

 

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