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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

 

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.

PURPOSE To show the centrality of pre-drive route and destination selection.

SUMMARY A driver is on an extended driving vacation. He has stopped approximately 50 miles (80.5 km) from his destination to review motel options for the evening at his destination point. He accesses the IMSIS directory for the town he will be staying in, reviews several alternative motels, and selects three that are located in one specific area and look interesting. Before proceeding toward his destination, he makes a reservation using ATIS.

SYSTEM

FUNCTIONAL CHARACTERISTICS

IRANS
IMSIS

5.3 Pre-drive route and destination selection
5.4 Dynamic route selection
6.2 Services/attractions directory
6.3 Destination coordination

 

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.

PURPOSE To illustrate a grouping of functional characteristics from Cluster 1 (5.1, 5.2, 5.3, 5.4, 5.6, 7.1, and 8.2).

SUMMARY A driver commutes between her home and the office. The commute requires coordination between three different modes of transportation. She drives the first 10 miles (16.1 km) and then has to decide between taking the ferry across the Bay or driving around the Bay Area. Once she is on the other side of the Bay, she has to drive for another 5 miles (8.0 km) to a park–and–ride lot where she takes a bus to the office. However, she can choose to reject the bus option and drive an additional 10 miles (16.1 km) if the traffic is light. It is a cold winter day and the roads are icy. She needs to get to work in the shortest amount of time possible. She uses her ATIS to plan her trip to the office and to coordinate the travel between the different modes of transportation. After taking the ferry and paying the toll, and while traveling to the bus stop, her ATIS informs her of icy conditions on the road and of bus delays. She selects an alternate route and continues her drive to work.

SYSTEM

FUNCTIONAL CHARACTERISTICS

IRANS

5.2 Multi–mode coordination and planning
5.3 Pre–drive route and destination selection
5.4 Dynamic route selection
5.7 Automatic toll collection
8.2 Road condition information

 

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.

PURPOSETo illustrate a grouping of the functional characteristics found in Cluster 2 (6.2, 8.1, 8.3, 8.4, and 8.5).

SUMMARY A driver travels on a secondary road where there are numerous speed changes due to the presence of several small towns. As he is driving, IVSAWS detects a malfunction of the car's brakes. The driver takes notice of the message and continues to his destination. Later on, he receives another message of road construction ahead. The driver applies the brakes, but it is too late; the car collides with a construction vehicle merging from the side of the road. The ATIS activates the aid request to provide assistance to the driver, who is unconscious.

SYSTEM

FUNCTIONAL CHARACTERISTICS

ISIS
IVSAWS

7.3 Roadway regulatory sign information
8.1 Immediate hazard warning
8.3 Automatic aid request
8.5 Vehicle condition monitoring

 

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.

PURPOSE To illustrate a grouping of functional characteristics from Cluster 3 (6.1, 6.3, and 6.4).

SUMMARY A driver uses ATIS to travel from her hotel to a restaurant on the outskirts of town. While traveling, she receives notification that the engine's oil temperature is increasing. Fearing engine damage, she pulls off the road. The driver then identifies a service station close by. She requests the assistance of a tow truck and cancels her dinner reservation. She also communicates with her friend to inform her of the misadventure with the vehicle and to ask to be picked up at the service station.

SYSTEM

FUNCTIONAL CHARACTERISTICS

IRANS
IVSAWS
IMSIS

5.3 Pre-drive route and destination selection
6.2 Broadcast services/attraction
6.3 Destination coordination
6.4 Message transfer
8.3 Manual aid request
8.5 Vehicle condition monitoring

 

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.

PURPOSETo illustrate the sequencing type of interactions among various functional characteristics.

SUMMARY A driver vacationing with his family in an urban setting arrives at the airport in mid– afternoon and rents a car with an IRANS device installed. The family's plan is to go directly to their hotel located in the city 10 miles (16.1 km) from the airport. The weather is good, but there is a substantial level of congestion on the major highways between the airport and the hotel due to normal commuting traffic. After receiving a brief orientation on using IRANS at the rental office, the driver identifies his destination on the IRANS and requests the fastest route. The IRANS recommends a route that the driver accepts and he begins his trip to the hotel.

SYSTEM

FUNCTIONAL CHARACTERISTICS

IRANS

5.3 Pre-drive route and destination selection
5.5 Route guidance
5.6 Route navigation

 

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.

PURPOSE Toillustrate the branching type of interactions among various functional characteristics.

SUMMARYIt is Friday afternoon and a driver is following her IRANS' guidance in traveling back to her hotel from an appointment with a client. As she drives, she receives the broadcast signal of a nearby winery. She debates between continuing to her hotel or visiting the winery. She uses the ATIS to verify if the winery is open and makes a reservation for the next guided tour. Moments later, she requests a dynamic route change to proceed towards the winery.

SYSTEM

FUNCTIONAL CHARACTERISTICS

IRANS
IMSIS

5.3 Pre–drive route and destination selection
5.4 Dynamic route change
6.2 Broadcast services/attractions
6.3 Destination coordination

 

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.

PURPOSETo illustrate the interactions among various functional characteristics.

SUMMARY A real estate salesperson is meeting a couple at their residence. She plans on showing them several houses in a suburban area of a major city. She has selected houses in several different neighborhoods spaced around one side of the city. The neighborhoods can be reached by either highways or arterials. It is evening, there is a heavy rain, and there is an accident on one of the highways that could be taken. Two neighborhoods that would be reasonable starting points for the evening's viewing are approximately equidistant from the clients' current residence. The salesperson would like to go to the neighborhood that can be most easily reached first. Prior to picking up her clients, she enters the addresses of all of the houses in the IRANS. During the drive to her clients' house, she monitors the traffic congestion in the planned area of travel. When she arrives at the clients' residence, she requests a comparison of travel times and selects the route that is predicted to take the least time. She then reviews current traffic congestion. Finally, she picks up her clients and drives them to the first house.

SYSTEM

FUNCTIONAL CHARACTERISTICS

IRANS

5.1 Trip planning
5.5 Route guidance
5.6 Route navigation

 

Table 49. Description of Scenario P8.

PURPOSE To illustrate that the requirements generated by ATIS may impose high workload demands on the driver.

SUMMARY A business traveler is driving in the suburbs of a major city he is not familiar with during a heavy snowstorm at dinner time. He has selected a 20–mile (32.2–km) drive, recommended by the ATIS, from his hotel to his first destination that is predominantly on arterial roads. In fact,the drive is not a straight line, but rather a series of turns to various arterial roads (no highways). The heavy snow is making visibility poor and the roads icy. He requests that the ATIS provide him with street signs and interchange graphics as well as stop signs and lane–use control information. Halfway to his destination, he is informed of an accident and of his need to select an alternate route. As he is examining two alternatives, the ATIS warns him of an approaching emergency vehicle. He slows down, pulls over, and enters his route choice. After the emergency vehicle passes, he continues traveling to his destination.

SYSTEM

FUNCTIONAL CHARACTERISTICS

IRANS
ISIS
IVSAWS

5.3 Pre–drive route and destination selection
7.1 Roadway guidance sign information
7.3 Roadway regulatory sign information
8.1 Immediate hazard warning
8.2 Road condition information

 

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.

 

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FHWA-RD-95-176

 

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