Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
SAE J2831-2020: Engineering Guidelines for In-Vehicle Alphanumeric Messages
🛠️ Note: this article focuses on engineering interpretation, not clause-by-clause translation.
In-vehicle information systems (IVIS) are integral to modern driving, providing critical data ranging from navigation instructions to vehicle status alerts. However, poorly designed alphanumeric messages can significantly increase driver distraction and compromise safety. The SAE J2831-2020 standard offers a framework for developing messages that are both informative and non-disruptive. This article distills the key design and engineering recommendations from the standard, focusing on content, format, and presentation parameters that directly impact driver performance.
Understanding Driver Performance and Message Design
The foundation of effective message design lies in acknowledging driver performance limits. The standard references models of visual sampling, such as Wierwille’s (1993) model, which highlights that drivers sample in-vehicle displays in brief glances, typically lasting less than two seconds. This naturally limits the amount of information that can be safely processed. Therefore, messages must be concise and prioritize critical information.
Moreover, the “life of a message” concept underscores that messages have a lifecycle—from initiation to comprehension and action. The design must facilitate quick understanding without requiring extended visual attention. The standard emphasizes that message urgency and driving context must dictate presentation style. For instance, a high-urgency warning requires immediate attention and should be displayed prominently, while an informational message can be deferred when the driving task is demanding.
Key Recommendations for Message Content and Format
The standard provides specific guidance on crafting message content and format to balance informativeness with safety. Key areas include message priority, length, style, and the use of fonts and colors.
Priority, Urgency, and Criticality
Messages should be classified by their urgency and criticality. Table 4-1 from the standard offers a summary:
| Urgency | Criticality | Context | Message Length | Structure |
|---|---|---|---|---|
| High | High | Immediate threat (e.g., collision warning) | Very short (1-2 units) | Direct command |
| Medium | Medium | Upcoming action (e.g., navigation turn) | Short (3-5 units) | Simple statement |
| Low | Low | Informational (e.g., fuel economy) | Moderate (up to 8 units) | Descriptive |
Note: Information units refer to simple words or short phrases.
Message Length and Style
Messages should be as short as possible while still conveying necessary information. The standard recommends using familiar abbreviations only when widely accepted (see Appendix A of the standard). Stylistically, warnings should use imperative or alerting language, while informational messages can be more conversational.
Engineering Design Insight: Conciseness is paramount. A message like “Tire Pressure Low” is preferable to “Warning: The tire pressure in your left front tire is below the recommended level.” Every extra word increases reading time and distraction potential.
Font, Color, and Display Considerations
For ergonomic display characteristics, the standard refers to ISO 15008. High-contrast colors and clear, sans-serif fonts improve legibility. Avoid using color alone to convey urgency, as some drivers may have color vision deficiencies. Supplement with symbols or text.
Effective Presentation and Scrolling Strategies
How a message enters and leaves the display significantly affects driver workload. The standard covers state change indication, message entry, and scrolling strategies.
State Change and Message Initiation
Clear visual or auditory cues should indicate when a new message appears. Avoid abrupt changes that might startle the driver. For example, a subtle chime combined with a visual indicator can signal a new message without causing distraction.
Common Mistake: Implementing auto-scrolling text that moves continuously without driver control. This forces the driver to track moving text, increasing cognitive load and glance duration. Always allow the driver to control the pace.
Scrolling Strategies
When messages are too long to fit in the display, scrolling becomes necessary. The standard warns against automatic scrolling that cannot be controlled by the driver, as it can lead to increased reading time and errors. Preferred methods include page-based presentation where the driver can manually advance, or smooth scrolling with user control. Avoid marquee-style continuous scrolling.
Frequently Asked Questions
1. What is the optimal message length for a warning?
For high-urgency warnings, ideally 1-2 information units (e.g., “Collision Risk” or “Lane Departure”). This allows quick comprehension in a single glance.
2. Should I use abbreviations in in-vehicle messages?
Only use abbreviations that are widely accepted and unambiguous. Standard abbreviations (e.g., “mph” for miles per hour) are acceptable, but avoid niche acronyms. Refer to Appendix A of SAE J2831 for a list of accepted abbreviations.
3. How can I indicate message urgency without using color alone?
Combine color with text modifiers like “Caution” or “Warning,” and consider using icons or symbols. This ensures the message is accessible to all drivers, including those with color vision deficiencies.
4. What is the best way to present a long message?
Break the message into pages or short segments that the driver can advance manually. If scrolling is necessary, provide user controls (e.g., scroll wheel or button) and avoid continuous auto-scroll.
