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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)





Introduction: Symbol contrast refers to the relationship between the luminance of a symbol and the luminance of the symbol's background. Contrast requirements have not been empirically studied under a wide range of representative driving situations and conditions, and there are few empirical data that can be directly used to specify design guidelines for the symbol contrast of automotive ATIS displays.

(Equation 1)

Here, we define contrast as a ratio between maximum and minimum luminance values or:

Contrast ratio = (Luminancemax / Luminancemin)


Luminancemax = luminance emitted by the area or element of greatest intensity

Luminancemin = luminance emitted by the area or element of least intensity



Introduction: Symbol height refers to the vertical distance between the top and bottom edges of an unaccented letter or number. Since ATIS devices can be used at a broad range of display distances, symbol height is best defined and specified as the visual angle subtended by the symbology (at the driver's eye), in minutes of arc.

(Equations 2, 3, and 4)

If Known

Use These Formulas for Calculating These Unknowns

Visual Angle

Symbol Height


Distance and Symbol Height

Arc tan (Symbol Height)
Distance (Eq. 2)

– –

– –

Distance and Visual Angle

– –

Distance x (tangent (Visual Angle)) (Eq. 3)

– –

Visual Angle and Symbol Height

– –

– –

Symbol Height
Tangent (Visual Angle)


Symbol Height = the height of the symbology

Distance = distance from viewers eyepoint to the display

Visual Angle = angle in degrees

Height and Distance use the same unit of measure



Introduction: Symbol luminance uniformity refers to the consistency of luminance values across a display.

(Equation 5)

Measuring segment of element ukniformity

(Equation 6)

Measuring whole-display uniformity


Luminancemin = the smaller luminance value

Luminancemax = the greater luminance value


Introduction: Color contrast refers to the relationship between symbol and background associated with chromatic differences such as hue and saturation. Determining the amount of contrast provided to the driver becomes a more complex problem when the symbology and/or the background are colored.

(Equation 7)

Equation for Determining Color Contrast


Introduction: Message style refers to the way in which information is given to the driver. The information can be presented in an advisory manner ("command style") or in more of a descriptive manner ("notification style"). Command style messages inform drivers of a situation and suggest a particular action to take in response to that situation. Notification style messages simply inform drivers and allow them to determine the appropriate action on their own. Message style should be selected based on an evaluation of the criticality of the situation and the need to make a control action immediately.

(Equation 8)

"Immediate" is defined as an inceident or condition which occurs within "X" meters of the vehicle's current position, where:

X = (Speed (in km/h) x 1.637) + 14.799


Introduction: The automotive HUD is an electro–optical device that presents both static and dynamic symbology and/or graphics in the driver's forward FOV. Presenting navigation information to drivers through HUDs is possible due to recent developments in automotive design, electronic instrumentation, and optics.

(Equation 9)

The Luminance Control Function for an automotive HUD

Footlambert = [(P x Lmax0.33) + ((1–P) x (Lmin0.33))] (1 ) 0.33)


P = the proportion of total control movement

Lmax = maximum luminance provided

Lmin = minimum luminance provided


Introduction: The timing of auditory navigation information refers to the time or distance at which ATIS should present an auditory instruction to the driver before an approaching navigation maneuver (e.g., a required turn).

(Equations 10, 11, and 12)

Equations for Determining the Appropriate Timing of an Instruction




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