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Federal Highway Administration Research and Technology
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Publication Number: FHWA-RD-98-057
Human Factors Design Guidelines for Advanced Traveler Information Systems (ATIS)and Commercial Vehicle Operations (CVO)
CHAPTER 4: GENERAL GUIDELINES FOR ADVANCED TRAVELER INFORMATION SYSTEM (ATIS) CONTROLS
This chapter provides human factors design guidelines relevant to the controls associated with ATIS devices. ATIS controls represent the primary means by which the driver interacts with the system and, therefore, their design is critical to successful use of ATIS devices. The following design topics are included in this chapter:
SELECTION OF CONTROL TYPE
Introduction: Selection of control type refers to the apparatus by which the driver makes control inputs (i.e., push–buttons, push–pull knobs, rotary knobs (discrete and continuous), levers, slides, thumbwheels, toggle switches, or rocker switches). Selection of appropriate control types is important to decisions regarding control location, because some control types are more suited to particular locations, and, conversely, particular locations are ideal for certain types of controls.
Supporting Rationale: Controls vary not only in terms of their functions, applications, and methods of operations, but also with respect to such characteristics as their relative space requirements, the likelihood of accidental activation, and the ease with which the position of the control can be identified. These characteristics should be considered when determining the method of operation and control type for secondary automotive controls.
Special Design Considerations: Selection of a control type is an iterative process, involving trade–offs between a variety of competing design concerns. In particular, control selection requires an analysis of the following driver–vehicle system considerations (adapted from Reference 1): (1) the function of the control, (2) the desired location of the control, (3) the requirement of the control task, (4) the vehicle environment, and (5) the consequence of driver error.
*Primarily expert judgement
CONTROL MOVEMENT COMPATIBILITY
Introduction: Control movement compatibility refers to the expected relationships between control actuation movements and the corresponding movements or changes in the system being controlled. Making control movements consistent with the driver's expectations can decrease reaction times, learning times, and control errors, and increase driver satisfaction with the vehicle's controls.
Recommended Control Movement–to–System Function Relationship
Supporting Rationale: The control–movement–to–system–function relationships are recommended based on a review of several different human factors sources (see References 1 and 2). The optimum direction of movement for a given control depends on a number of factors, including: (1) the position of the operator relative to the control, (2) the position and direction of movement of any associated display, (3) the change resulting from the control movement, and (4) the control–movement–to–system–function relationships for other controls that the driver uses.
Special Design Considerations: According to Reference 3, it may be necessary to violate one compatibility relationship in order to take advantage of another one in the design of a system. An example of this is the rotary stalk control. In order to increase some parameter using the left–hand stalk, the control must be rotated up or counterclockwise. Although up is the correct movement for increasing a system function, counterclockwise is not. Therefore, the designer must determine which of the driver's expectations is stronger or which can be violated without affecting the driver's ability to effectively use the system.
*Primarily expert judgement
Introduction: Control coding refers to the design characteristics of controls that serve to identify the control or to identify the relationship between the control and the function to be controlled. Proper coding of controls will increase the probability that the controls will be quickly and accurately located by drivers, thus reducing the eyes–off–road time.
Recommended Minimum Control Separation1 Distances
Supporting Rationale: Several sources (see Reference 1 and 2) have provided recommendations for minimum distances between controls. Most of these recommendations have been developed for application in environments other than automobiles. However, they provide helpful information regarding location coding and avoidance of inadvertent activation of adjacent controls.
Shape coding is an effective way to increase the identifiability of controls and is most often used on rotary knobs. Most standard human factors references provide graphics showing knob shapes that are rarely confused with one another. See Reference 3 for some of these knob designs.
Size coding is most appropriate when ganged controls are used (i.e., two or more knobs mounted on concentric shafts). Different knob diameters must be used if the ganged controls are to be discriminable from one another. In automobiles, for example, volume and tone controls on the radio system are often ganged. Suggestions for different knob dimensions can be found in References 2 and 4.
There are three methods of texture coding that are rarely confused with one another: smooth, fluted (horizontal lines), and knurled (crisscross pattern). However, different methods and amounts of either fluting or knurling may be confused with each other.
Special Design Considerations: Because drivers are most often operating in–vehicle controls without taking their eyes off the roadway, it is important that they be as easy to locate and activate as possible. Coding can be extremely helpful for accomplishing this. However, in situations where gloves are used, redundant coding using colors and labels may become necessary.
*Primarily expert judgement
SELECTION OF KEYBOARDS FOR ATIS DEVICES
Introduction: Selection of keyboards for ATIS devices refers to trade–offs and heuristics associated with fixed–function vs. variable–function keyboards. As discussed in Reference 1, examples of a fixed–function keyboard include cash register terminals and hand–held calculators; examples of a variable–function keyboard include keyboards for video games with different controls for different games, shifted keys of computer keyboards, and, in general, "soft" keys that can be changed via software control.
Advantages and Disadvantages of Fixed– and Variable–Function Keyboards (from Reference 1)
Supporting Rationale: The guidelines provided above reflect a review and analysis of fixed– vs. variable–function keyboards reported in Reference 1. They reflect common usage of both fixed– and variable–function keyboards, as well as general heuristics for their selection.
Special Design Considerations: It may be desirable to design ATIS devices so that they include both fixed– and variable–function keyboard elements. Functions that are common across ATIS tasks such as "Enter" or "Back" or "On/Off" might best be accomplished by using dedicated, fixed–function (or "hard") controls. Functions that involve selecting from among alternatives that vary from task to task (selection of: system functions, map scale, travel mode, etc.) might be best accomplished by using nondedicated, variable–function (or "soft") controls.
Also, while many devices can provide the driver with the ability to communicate with an ATIS (e.g., touch screens, speech controls, trackballs, push–buttons), keyboards are best for tasks that involve great amounts of text input, such as entering addresses for Routing and Navigation applications or entering preferences and services selection information for Motorist Services applications.
DESIGN OF SPEECH–BASED CONTROLS
Introduction: Design of speech–based controls refers to systems that recognize human speech and treat speech commands as inputs to the ATIS system. As discussed in Reference 1, automatic speech recognition (ASR) systems may be characterized with respect to three sets of design characteristics. First, speaker–dependent systems recognize speech from only one speaker that has been calibrated to the system; speaker–independent systems can recognize speech from many speakers. Second, isolated word recognition systems require that speakers provide a pause or gap between words in a message; continuous speech recognition systems do not require any pause between words. Third, ASR systems vary with respect to the size of the vocabulary that they recognize.
Issues to Consider When Designing ASR Systems
Supporting Rationale: Reference 2 provides considerable discussion of issues and research related to speech controls; the guidelines presented above have been adapted from design principles presented in Reference 2 and, to a lesser extent, Reference 1. The guidelines presented above reflect limited experience in the use of speech as a control device from two technical domains: (1) military information systems and flight control, and (2) the telecommunications field. Case studies and anecdotal results from several applications of speechcontrols can be found in References 1 and 2. Although various commercial speech recognition systems have been developed for automotive applications, published empirical results are few and have not always provided consistent design guidance.
Special Design Considerations: As noted in Reference 2, key issues in the design and implementation of ASR systems include:
PROVIDING DESTINATION PREVIEW CAPABILITY
Introduction: Providing destination preview capability refers to providing the user with the capability to recenter (slew) the map and to change the range scale (magnification) to enable full preview of route details. The user of an electronic map displaying route information may desire to preview the origin, destination, or any segment of the route. The system design should, however, distinguish clearly between a recentered map mode (i.e., vehicle in center of display) and the normal display mode (i.e., vehicle moves relative to stationary map) showing current position of the user/vehicle. Failure to clearly distinguish between these two modes can result in confusion about current location.
Grand View of Long Route; Detailed View of One Node Recentered
Important Note: The map display depicted above is provided solely to augment this Design Guideline by illustrating general design principles. It may not be suitable for your immediate application without modification.
Supporting Rationale: As described in Reference 1, the utility of electronic maps is multiplied by incorporating the combination of a map scale control and recenter function. The combination of scale control and a recentering function enables the user to preview any area of the map in greater detail. The user can have a Ahigh level overview of a long route or a closer look at more detailed features pertinent to turns, areas of potential navigation errors, the destination, or other areas of interest. With the magnified view, the map must be recentered to achieve a detailed view of a more distant map location.
Special Design Considerations: In–vehicle navigation displays typically depict the vehicle near the center of the display screen. When the user recenters the map, the vehicle symbol will no longer be in the normal location relative to the screen. This can lead to user confusion about current vehicle location, particularly if the user=s attention is turned elsewhere after recentering. The benefits derived from empowering users to recenter the map must be weighed against the potential for misinterpretations of current location. Protection against this type of error can be designed into the system by displaying a caution indicator or by locking out the recenter function when the vehicle is in motion. If users are allowed to slew or recenter the map while in motion, a simple one–button return to the normal, user–vehicle–centered mode is recommended. A mode that allows the vehicle to always remain in the center of the screen may also be provided.