Research Update

The Human Centered Systems

Research Program addresses human

performance-related issues that affect

highway system design. Current

human centered research focuses on

Highway Safety and Intelligent

Transportation Systems (ITS).

Human centered research products

include driver performance models,

highway system design guidelines,

and handbooks based upon empirical

human performance data collected in

the laboratory and in controlled,

on-the-road tests.

Research, Development, and Technology

Turner-Fairbank Highway

 Research Center

6300 Georgetown Pike

McLean, Virginia 22101-2296

IMPROVING DRIVER RECOGNITION OF

IN-VEHICLE ICONS

HUMAN CENTERED

SYSTEMS

Introduction

This research update provides general human factors design information relevant to

the early phases of in-vehicle icon development and design. It reflects a subset of the

results to date of a Federal Highway Administration (FHWA) project to develop a set

of clear, concise, and user-centered human factors design guidelines for in-vehicle

icons. An important element of this project is the involvement of a project working

group, consisting of more than 20 representatives from the icon design, intelligent

transportation systems (ITS), and human factors communities. This group has served

as subject matter experts and consultants to the project, helping to ensure that the

resulting design guidelines conform to icon designers’ specific needs with respect to

content, organization, and format.

Icons are visual representations or images used to symbolize an object, action, or

concept. Icons are among the oldest forms of communication and provide a number

of advantages over a text-only approach to presenting drivers with in-vehicle messages. For example, icons: (1) may be recognized more quickly and accurately than

text-only messages, (2) can be presented in a much smaller area than can text, and (3)

can convey information across many languages and cultures.

Despite the obvious applicability of icons to the design of ITS, such as advanced

traveler information systems (ATIS) and collision avoidance systems (CAS), poorly

designed icons can lead to driver confusion and errors and can actually exacerbate

existing traffic problems. Although the use of icons is widespread, few guidelines

exist that can be used confidently by vehicle and electronics designers during icon

development. The lack of guidelines, standards, and a systematic framework to aid

icon design has resulted in design by consensus for many ITS-related icons, a lack of

scientific rigor in icon development, nonintuitive and difficult-to-learn icons for invehicle messages, and multiple icons for the same message.

Human Factors Design Guidelines to Increase Driver

Recognition of In-Vehicle Icons

A key element of icon comprehension and use by drivers is the extent to which invehicle icons can be quickly and easily recognized by drivers. Icon recognition

reflects the relationship between the driver, the icon, and other icons or visual display

elements. Icon recognition will depend on design issues such as the shape of the icon,

figure/ground relationships, level of detail, use of overlapping elements, and

discriminability from other symbols. Of the 36 preliminary design guidelines that

have been produced for this project, an entire chapter (5 guidelines) has been devoted

to the topic of icon recognition. Design guidelines associated with three areas that

influence recognition of icons are summarized below, reflecting key design questions

such as: (1) What basic principles of perception can be used to increase icon recognition? (2) What is the appropriate level of detail for in-vehicle icons? and (3) What is

the appropriate level of realism for in-vehicle icons?
Figure 1. Key perceptual principles for icon design.

Icon Design Parameter Recommendation Do This... ...Not This

Figure/Ground Emphasize a clear, stable, and solid

Relationship relationship between a symbol and its

background.

Figure Solid shapes are better than thin line

Boundaries boundaries or dotted-line boundaries

unless the element in question is

depicting action or movement.

Closure Use closed figures instead of figures

with discontinuous lines, outlines, or

disjointed elements.

Simplicity Icons should be simple with only the

necessary detail included.

Unity All parts of the symbol should be

enclosed within a single boundary.
Figure 2 . Example of appropriate level of detail.

What basic principles of perception can be used

to increase icon recognition?

Many of the perceptual principles about how we

decode and comprehend symbols have come from

the ideas and experiments that were completed by

Gestalt psychologists around the turn of the

century. These perceptual principles reflect the

notion that the structural properties of symbols

and icons are important determinates of their

perceptibility and, hence, recognition and usefulness. Figure 1 (to the left) highlights some of

these perceptual principles.

What is the appropriate level of detail for invehicle icons?

Only those details that will add to the meaning of

an icon or symbol should be included in the design

of an icon, while those that distract from the true

goals of recognition and comprehension should be

omitted. Figure 2 shows an example of the

appropriate level of detail for an in-vehicle icon.

The following are key human factors design guidelines for

determining level of detail for icons:

• Design symbols on a 20 x 20 unit grid, making sure that

no significant detail is smaller in size than 1 square unit.

• Significant details within a symbol should subtend, at a

minimum, 3 degrees of visual angle.

• Line thickness for a significant detail should subtend, at a

minimum, 2 degrees of visual angle.

What is the appropriate level of realism for in-vehicle icons?

Level of realism refers to the style in which a symbol is drawn.

Deciding whether to use a detailed, realistic style or a simplified style can have a great impact on the recognizability of

symbols. Including detail in the design of some symbols and

icons can make them easier to recognize, while adding detail to

others can make them harder to recognize. Figure 3 (see next

page) presents some design guidelines and examples of the

appropriate level-of-realism for an in-vehicle icons.

Future Guideline Development Activities

The 36 preliminary guidelines developed so far in this project

reflect an integration of existing empirical studies, literature

reviews, and icon design principles. The guidelines represent only a necessary first step toward the larger project

goal of developing a clear and comprehensive human

factors design handbook for in-vehicle icons that can be

used throughout the in-vehicle icon design process. The

preliminary guidelines provide both a valuable resource for

icon designers as well as a “roadmap” that indicates key

design topics for which design guidelines are needed, but

little empirical data exist that can be used to develop them.

The next phase of this project will involve conducting a

series of empirical studies that will address critical icon

design issues. The final version of the handbook will reflect

the results of these empirical studies, as well as reviews of

the preliminary guidelines conducted by the project working

group and others from the icon design community.

References

Horton, W. K. (1994). The Icon Book: Visual Symbols

for Computer Systems and Documentation. New York:

J. Wiley & Sons.
Issued April 2000 Publication No. FHWA-RD-00-091

Researcher—This study was performed by the Battelle Human Factors Transportation Center, 4000 N.E. 41st

Street, Seattle, Washington 98105. The principle investigator for the contract is John L. Campbell, Ph.D.

Distribution—This technical summary is being distributed according to a standard distribution. Direct distribution is being made to the Resource Centers, Divisions, and the customers in the automotive industry.

Availability—The guidelines document will be available in the fall of 2001.

Key Words—In-vehicle information systems, icons, symbols, advanced traveler information systems, intelligent

vehicle initiative.

For More Information—Contact Thomas M. Granda, Team Leader, HRDS, (202) 493-3365 or Christopher Monk,

Research Psychologist, SAIC, (202) 493-3382.

Notice—This Announcement is disseminated under the sponsorship of the Department of Transportation in the

interest of information exchange. The Announcement does not establish policies or regulations, nor does it imply

FHWA endorsement of the conclusions or recommendations. The U.S. Government assumes no liability for the

contents or their use.

Figure 3. Five levels of icon realism (from Horton, 1994).

Example Level of Realism Design Style When to Use

Photographic

Realism

Simplified

Drawing

Caricature

Outline

Silhouette

Photographs and

photographic

Outline with distinct

interior details

Exaggeration of

crucial details

Outline with only

prominent details

Shape filled with solid

color contrasting with

background

Use for presenting complex symbols with a lot

of detail (e.g., specific people, buildings,

or landmarks).

Use for presenting complex symbols with small

significant parts, especially when the objects

have similar profiles (e.g., mechanical or

electrical devices).

Use for presenting those symbols that have a

small, crucial feature or for simplifying

complex details.

Use for presenting small symbols that represent

a familiar object with a distinct profile.

Use for presenting symbols that are too thin to

show in outline format and for symbols that

have a very distinct profile and do not

require detail for recognition.