Controls, Displays, and
Interior Layouts
The driver obtains information available from different displays (e.g., speedometer, fuel gauge,
radio display, warning lights, warning sounds, symbols, labels, road views from the windshield and
window openings, inside and outside mirrors, etc.) and generates outputs (e.g., moves pedals and
the steering wheel, pushes buttons, turns stalks, etc.) to control the vehicle motion and/or change
the states of different in-vehicle devices (e.g., change radio station). To obtain information from
displays and operate controls, the driver uses various information-processing and control-activation
capabilities. Depending on the levels of different capabilities and available resources, the driver
may or may not make an appropriate control action. The time taken by the driver to make a control
action will also depend on the amount of information that the driver will need to process and his
or her information-processing capabilities. If the controls and displays are not designed for ease in
performing these tasks, the driver may not be able to complete the tasks within the available time
or make errors.
The controls and displays design research began with studies of pilot errors (Fitts and Jones,
1961a and 1961b). Soon after World War II, the Air Force launched a systematic study of errors made
by pilots in situations where accidents and near accidents occurred. The pilots were asked to recall
incidents where they almost lost an airplane or witnessed a copilot make an error in reading aircraft
displays or operating controls. From the analyses of the data gathered from these critical incidents,
Fitts and Jones found that practically all the pilots, regardless of experience or skill, reported mak-
ing errors in using cockpit controls and instruments. They also concluded that it should be possible
to eliminate or reduce most of these pilot errors by designing equipment in accordance with human
requirements. Similarly, driver errors in using displays and controls can be reduced if they are
designed in accord with the human engineering criteria.
Chapter 4 provided basic information on driver information processing, driver errors, and
some information-processing-based guidelines for designing controls and displays. This chapter
is intended to provide information on many important considerations and issues in designing and
evaluating controls, displays, and their layouts.
The controls and displays are the interface between the human operator (the driver) and the machine
(vehicle). Figure 5.1 illustrates this interface. Thus, the problem of controls and displays design is
regarded as a problem of human–machine interface design.
In designing the driver interface, the vehicle designer should always keep in mind the following
basic considerations:
1. Drivers will prefer to minimize their mental and physical efforts in using controls and
2. People will prefer not to use what they do not understand.
3. Study the user population, user characteristics, and the variability among the users in the
population. Characteristics of users (such as their age, familiarity with the equipment

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