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Publication Number: FHWA-RD-95-176
Development of Human Factors Guidelines for Advanced Traveler Information Systems and Commercial Vehicle Operations: Task Analysis of ATIS/CVO Functions
APPENDIX B. FUNCTION AND SCENARIO SELECTION
Private Vehicle Scenarios
Private Driving Scenarios Based on Frequency Count and Centrality Measure
The frequency count analysis and the centrality measure analysis showed that pre-drive route and destination selection was the functional characteristic that had the greatest number of interactions with other functions and that was also considered the most central. Scenario P6 (see table 42) was chosen because it was one of the original scenarios developed in Task B and because it included pre-drive route and destination selection and other functional characteristics that were considered relatively central as well (e.g., destination coordination).
Table 42. Description of Scenario P6.
Private Driving Scenarios Based on Functional Clusters
The cluster analysis organized the functional characteristics into a pre–selected number of groups, or clusters. Out of the five specified clusters, three formed meaningful groupings. Each cluster represents a grouping of functions that are related to more than one ATIS subsystem. Considering that each cluster grouped functional characteristics that were linked together according to the network analysis, they formed fairly homogeneous groups. The first cluster includes functional characteristics related to planning and navigation, the second cluster is associated with aid and emergency services, the third cluster has to do with travel coordination.
For each one of these clusters, a scenario was chosen that illustrates one particular situation in which these functional characteristics are interacting together. However, it is important to note that these scenarios illustrate one of several possible alternatives for combining these various functions into one situational context.
Alternatively, it is interesting to consider scenarios that illustrate interactions between different clusters in addition to interactions between functions within the same cluster. In this regard, Scenario P6 (above) is one such example that shows an interaction between the three different clusters. The interest in these cluster interactions stems from the fact that these particular scenarios not only show the requirements of supporting a task that requires the interactions with different subsystems, but also tasks that require a diverse set of functions.
Cluster 1. This cluster groups functional characteristics that span across three different ATIS subsystems, although the emphasis is mainly on IRANS. This cluster is also the largest of the three, grouping on the whole with seven different functional characteristics. Table 43 is a description of Scenario P14.
Table 43. Description of Scenario P14.
Cluster 2. This cluster of functional characteristics focuses mainly on aid requests as well as on emergency services needs. Most of the functions included in this cluster are related to IVSAWS, except for the services/attractions directory that is provided by IMSIS. As shown in table 44, this particular scenario uses three out of the five possible functional characteristics.
Table 44. Description of Scenario P22.
Cluster 3. This cluster facilitates the travel coordination required by a driver going to either a service facility or a tourist attraction. In addition, this cluster enables the coordination between parties if one of them needs to be informed of delays or other unusual circumstances. Scenario P16 reflects multiple interactions with the system and, at the same time, combines the three functional characteristics that make up Cluster 3 (see table 45).
Table 45. Description of Scenario P16.
Private Driving Scenarios Based on the Nature of Task Interactions
As illustrated in the scenarios above, functional characteristics, either ATIS–related and/or driving–related, have a tendency to operate in groups. In some instances, several functions originate from only one specific ATIS subsystem. In other circumstances, one or several functional characteristics from two subsystems or more are used in the same situational context. The nature of the interactions between these various functional characteristics varies and has some important implications for the task analysis breakdown. In fact, the interactions between various functional characteristics can be categorized into three different types: (1) sequential, (2) branching, and (3) recursive. Each of these types of interactions will be described in one of the following subsections. Although it is possible to be in an environmental context that could combine the three different types of interactions, for ease of clarity, the present task analysis will focus on scenarios that illustrate only one type of functional interaction at a time.
Private driving scenario based on sequential functions. This type of interaction is the simplest of all three types, as each functional characteristic occurs in sequence with the other. In other words, the driver has to complete a set of tasks associated with a particular function before he or she can proceed with the other functions.
Scenario P1 was chosen to illustrate the nature of sequential functions for four reasons: (1) it is a scenario that was designed as part of Task B and did not need to be modified; (2) it focuses on the pre–drive route and destination selection, which is the most central measure; (3) it is relatively simple, using only three functional characteristics that belong to the same subsystem, IRANS; and (4) it includes two functional characteristics that were not included in any of the scenarios chosen so far (see table 46).
Table 46. Description of Scenario P1.
Private driving scenario based on branching functions. When a driver has completed a sequence of tasks from one particular functional characteristic and is at a way–point having to choose between two different functions, each with its particular set of tasks, the driver is, in fact, choosing between two different branches of the task descriptions (see table 47). When the driver chooses to accomplish function "A," for example, he or she will not accomplish function "B." By choosing "A" instead of "B," the driver defines the path taken. In some instances, the sequence of functions is the same whether the driver chooses "A" or "B"; in other circumstances, the path will remain different throughout the entire remainder of the sequence.
Table 47. Description of Scenario P20.
Private driving scenario based on recursive functions. In this instance, the functions are not following each other in a sequence, but rather require that the driver repeat a step that previously had been partially or entirely completed. In other words, this type of interaction implies that a driver can accomplish a given set of tasks associated with a given function, continue to another function, and come back to that first function later on. The rationale for such a set of interactions is that the outcome of one particular functional characteristic may require additional information or transformation before proceeding to the next one.
Scenario P2 (shown in table 48) was chosen for three different reasons. First, it illustrates a type of interacting functions that could be repeated more than once, if needed. Second, this scenario was also favored because it originated from Task B's initial set of scenarios. Finally, Scenario P2 adds one more function (trip planning) to the overall set of functional characteristics analyzed so far.
Private Driving Scenario Based on High Workload Demands
One of the main concerns of the implementation of these ATIS is that they interact with the existing driving tasks. In fact, it becomes essential to investigate to what degree ATIS demands will impair or facilitate the driving task. In some instances in which the driver is required to operate under high demands, such as traveling in an unknown city during bad weather, the ATIS might be more negative than beneficial. The purpose of this scenario is to provide an example of how various functions could interact during an already demanding driving task (see table 49).
Table 48. Description of Scenario P2.
Table 49. Description of Scenario P8.
the driver chooses to accomplish function "A," for example, he or she will not accomplish function "B." By choosing "A" instead of "B," the driver defines the path taken. In some instances, the sequence of functions is the same whether the driver chooses "A" or "B"; in other circumstances, the path will remain different throughout the entire remainder of the sequence.