CHAPTER 4: GENERAL GUIDELINES FOR ADVANCED TRAVELER
INFORMATION SYSTEM (ATIS) CONTROLS

CONTROL CODING

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.

Design Guidelines***

Use one or more of the following design characteristics to identify controls:
  • Location Coding: In order to ensure discriminable and unique control locations, controls must be separated by distances that are sufficient to avoid confusion among positions (see table below entitled "Recommended Minimum Control Separation Distances").
  • Shape Coding: This is most effective when used in combination with location coding. Errors in the driver's hand position are indicated by the feel of the control.
  • Size Coding: This is most effective when used in combination with location coding. As many as two or three sizes can be used to discriminate controls. In general, size coding is most effective if the diameter of the outermost control is 1/2" (1.27 cm) larger than the next-closest control on the stalk.


Recommended Minimum Control Separation1 Distances

Control

Push-Buttons (No Array)

Push-Button Arrays

Rocker Switches

Toggle Switches

Thumb-Wheels

Discrete Rotary Controls

Continuous Rotary Controls

Push-Buttons

(No Array)

0.5 in

(1.27 cm)

2.0 in

(5.08 cm)

0.5 in

(1.27 cm)

0.5 in

(1.27 cm)

0.5 in

(1.27 cm)

0.5 in

(1.27 cm)

0.5 in

(1.27 cm)

Push-Button Arrays

2.0 in
(5.08 cm)

2.0 in
(5.08 cm)

1.5 in
(3.81 cm)

1.5 in
(3.81 cm)

1.5 in
(3.81 cm)

2.0 in
(5.08 cm)

2.0 in
(5.08 cm)

Rocker Switches

0.5 in
(1.27 cm)

1.5 in
(3.81 cm)

0.5 in
(1.27 cm)

0.75 in
(1.91 cm)

0.5 in
(1.27 cm)

0.5 in
(1.27 cm)

0.5 in
(1.27 cm)

Toggle Switches

0.5 in
(1.27 cm)

1.5 in
(3.81 cm)

0.75 in
(1.91 cm)

0.75 in
(1.91 cm)

0.5 in
(1.27 cm)

0.75 in
(1.91 cm)

0.75 in
(1.91 cm)

Thumb-Wheels

0.5 in
(1.27 cm)

1.5 in
(3.81 cm)

0.5 in
(1.27 cm)

0.5 in
(1.27 cm)

0.5 in
(1.27 cm)

0.75 in
(1.91 cm)

0.75 in
(1.91 cm)

Discrete Rotary Controls

0.5 in
(1.27 cm)

2.0 in
(5.08 cm)

0.5 in
(1.27 cm)

0.75 in
(1.91 cm)

0.75 in
(1.91 cm)

1.0 in
(2.54 cm)

1.0 in
(2.54 cm)

Continuous Rotary Controls

0.5 in
(1.27 cm)

2.0 in
(5.08 cm)

0.5 in
(1.27 cm)

0.75 in
(1.91 cm)

0.75 in
(1.91 cm)

1.0 in
(2.54 cm)

1.0 in
(2.54 cm)

1Separation is measured between the outermost adjacent edges.

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.

Cross References:

Selection of Control Type

Control Movement Compatibility

Key References:

1. Nuclear Regulatory Commission. (1981). Guidelines for control room design reviews (NUREG-0700). Washington, DC: U.S. Government Printing Office.

2. Boff, K. R., & Lincoln, J. E. (Eds.). (1988). Engineering data compendium: Human perception and performance. Wright-Patterson Air Force Base, OH: Armstrong Aerospace Medical Research Laboratory.

3. Hunt, D. P. (1953). The coding of aircraft controls (Technical Report 53-221). Wright-Patterson Air Force Base, OH: Wright Air Development Center.

4. MIL-STD-1472D. (1989). Human engineering design criteria for military systems, equipment, and facilities. Washington, DC: U.S. Government Printing Office.

*Primarily expert judgement
** Expert judgement with supporting empirical data
***Empirical data with supporting expert judgement
****Primarily empirical data

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