U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
|This report is an archived publication and may contain dated technical, contact, and link information|
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 Decision–Making Tasks
Decision making is an important part of any information system, including ATIS. The analysis of decision–making tasks is intended to provide an understanding of this type of activity with regards to ATIS.
Function of Decision–Making Tasks
Decision–making tasks provide the most important human activity in the use of ATIS. These tasks include activities where the driver or dispatcher compares alternatives against expectations, verifies that system recommendations are appropriate, and ensures that following system recommendations can be done safely. Decision–making tasks inherently involve the comparison of two conditions (e.g., system output and expected output). They also inherently result in following one of two possible (and often divergent) task sequences. Examples of decision tasks associated with ATIS include:
Table 20 describes the decision–making tasks identified in the task analysis that serve several functions.
Table 20. Function and description of decision–making tasks.
General Characteristics of Decision–Making Tasks
Of the 165 driver or dispatch–centered tasks examined in detail, approximately 21 percent were decision–making tasks. The decision–making tasks identified in the task analysis serve several functions. The first is that they are used to decide if the plans and recommendations of a particular system activity, such as planning a route, are what the driver or dispatcher intended (see figure 19; also see appendix D, Scenarios P1 OSD, P2 OSD, P6 OSD, P8 OSD, P14 OSD, P16 OSD, P20 OSD, and C4 OSD). Such decisions are important to the use of the ATIS because they provide the user an opportunity to include considerations in his or her planning process that the ATIS is unable to make. They also provide the driver an opportunity to correct information or assumptions made by the system that are manifestly inappropriate. This sort of decision task is normally associated with IRANS and IMSIS planning functions and would probably be performed when it could be done without interfering with the primary task of controlling the vehicle. The outcome of this task usually will be either to have the system develop another plan or to use the plan as presented.
Another type of decision task involves verifying that a specific recommendation is appropriate when it is presented during the IRANS route guidance instruction (see figure 20; also see appendix D, Scenarios P1 OSD, P2 OSD, P16 OSD, P20 OSD, and C4 OSD). Usually such decision tasks must be performed while also controlling the vehicle, thus requiring the driver to gather information upon which to make the decision from a variety of different areas (e.g., personal experience, observations of the road configuration, and observations of other traffic).
The results of this type of task usually are to follow the recommendations presented by the system or to ignore the recommendations and revert to driving without using the system until the discrepancy between the driver's perception of the situation and system recommendations can be corrected.
A third type of decision task is an evaluation of the relevance of ISIS and IVSAWS notices and warnings as they relate to driving (see figure 21; also see appendix D, Scenarios P8 OSD, P14 OSD, P16 OSD, P22 OSD, and C15 OSD). Such tasks are initiated when either ISIS or IVSAWS detects a condition that lies within the notification parameters selected by the driver or system. In most cases, notification will be made as a result of the vehicle coming within a certain distance of the condition, thus requiring the driver to perform this task while controlling the moving vehicle. The outcome of a decision task of this nature may be either to ignore the notification or to modify the driving behavior or planned routing.
One remaining type of decision task is evident in the detailed task analyses. This is a decision task that recognizes some change in the situation, other than that presented by ATIS, which might necessitate a change in plans or behavior (see figure 22; also see appendix D, Scenarios P14 OSD and C12 OSD). This type of task usually involves comparing the expected results of the plan currently being followed with some sort of "what if" analysis for another plan. The steps required to make such an evaluation are likely to be fairly complex as they would normally require that the driver have information on two, or possibly more, potentially competing plans. Generating those plans would normally require that the driver provide the system with different sets of parameters for developing the plans. Decision tasks of this type might be performed either while moving or when stopped. However, the need to provide the ATIS with alternative planning information would probably indicate that such decisions are most likely to be made when the vehicle is stopped, such as in a traffic backup.
Human Factors Design Implications (General and Specific)
Decision–making tasks such as those associated with using ATIS/CVO essentially involve comparisons between presented information and some criteria, such as knowledge, experience, or expected outcome. Although not presented in the detailed analysis due to limitations of space and the uncertainties associated with specific design possibilities, decision tasks involve a complex and often repeated series of gathering information, interpreting its meaning, and selecting from among possible alternatives. Performance on such tasks depends on the accuracy of the information as well as the thoroughness with which the driver can examine the problem presented.
Many of the decision–making tasks associated with ATIS planning functions will probably be done during the pre–drive phase of a trip, and thus afford the driver a reasonable opportunity to gather and evaluate whatever information is necessary to perform the task. Decision tasks that involve planning while also controlling the vehicle would significantly increase the workload required of the driver, both due to the intensive interaction that would be necessary to obtain information from the system and due to the cognitive load imposed by the amount of information that would be required.
Decision tasks associated with executing ATIS recommendations present similar workload concerns for the driver as when following directions given by a passenger. In both cases, the driver has to evaluate whether the instructions are appropriate and whether he or she can execute them safely. The performance characteristics of such tasks, while not at all unusual in driving without the ATIS, are of considerable importance and warrant further investigation, particularly as they are at least partially based on the driver's perception of the error rates of the system and the degree to which the driver has come to rely on system instructions.
Performance characteristics of decision tasks associated with ISIS and IVSAWS notifications and warnings are likely to be a little different than those now encountered when faced with roadside signs or hazard warnings. The principal difference is that the advanced warning that such systems can provide a driver will allow him or her more time to take appropriate action. Unlike conditions such as the IRANS planning and guidance that involve more complex decision–making processes, decisions based on ISIS and IVSAWS are likely to be straightforward and the required action is more likely to be based on a simple heuristic model (e.g., "ice = slow down" and "speed below limit = speed up").
General human factors considerations for the design of ATIS that result in decision tasks include the following:
Specific human factors design considerations for ATIS that result in decision tasks include the following:
Table 21 provides a summary of the general characteristics and considerations of decision–making tasks associated with the use of ATIS.
Table 21. Summary of the general characteristics and considerations of decision–making tasks associated with the use of ATIS.