Key Takeaways

  1. Car interfaces designed for pilots and astronauts: SAE guidelines assume expert users, but 95% of drivers are average people.
  2. Airport signs avoid design flaws cars embrace: Critical information placement and font size standards that automotive ignores.
  3. Voice alerts reduce psychological stress by 30%: HRV measurements prove auditory warnings outperform visual-only prompts.
  4. Touch targets too small for driving conditions: 19mm minimum vs. car industry's 12.5mm standard creates dangerous usability gaps.
  5. Color coding fails in real-world lighting: Automotive standards ignore how sunlight and shadows affect color perception.
  6. Mental models mismatch user expectations: Car interfaces follow aviation logic that confuses everyday drivers.

The Pilot in Your Passenger Seat

Modern cars contain more computing power than the Apollo 13 mission that brought astronauts home from disaster. Yet the human-machine interfaces (HMI) that control this technology were designed with fundamentally different users in mind.

95% of drivers are average people—not pilots or astronauts—yet car interfaces are designed for experts.

SAE International guidelines for automotive HMI design explicitly state they are based on “pilots and astronauts” as the user model1. This creates a dangerous mismatch: interfaces designed for highly trained specialists operating in controlled environments are used by everyday people in chaotic traffic.

The Critical Problem: Aviation interfaces prioritize precision and efficiency for trained operators. Automotive interfaces should prioritize safety and simplicity for untrained users. The current approach puts expert expectations on novice users.

Airport Signs Know Better

If automotive designers looked at other transportation interfaces, they’d find better design precedents. Airport signage standards provide a stark contrast to automotive HMI failures.

Airport Signs
CRITICAL INFO AT EYE LEVEL
Important information placed for standing viewers
Car Displays
CRITICAL INFO LOW
Speed and warnings placed for seated drivers

Airport signage standards require critical information to be placed at eye level for standing viewers. Car manufacturers place critical information (speed, warnings) at the bottom of displays where seated drivers naturally look2.

Font Size Standards: Airport signs have minimum font size requirements for readability at distance. Automotive displays often use fonts that become unreadable in bright sunlight or at speed.

"Airports design for people walking and reading signs. Cars design for people driving and glancing at displays. Yet somehow airports get the ergonomics right."

This contrast reveals how automotive HMI design has prioritized tradition over user-centered design principles.

Voice Alerts Reduce Stress Significantly

When cars provide warnings or information, the delivery method critically affects driver stress and effectiveness. Research using physiological measurements reveals clear design guidance.

-30%
STRESS REDUCTION
Voice alerts vs. visual-only warnings (HRV measurements)
Better
HRV vs. EYE TRACKING
More reliable metric for psychological stress assessment

Heart Rate Variability (HRV) measurements showed that voice-enabled prompts significantly reduced psychological load compared to visual-only alerts3. This provides clear evidence-based guidance for designing less stressful vehicle interfaces.

The Design Principle: Auditory information allows drivers to keep their eyes on the road while receiving critical information, reducing both cognitive load and stress.

Touch Targets Are Dangerously Small

Modern cars increasingly rely on touchscreens for controls, but the touch target sizes often violate basic usability principles for moving vehicles.

19mm
ERGONOMICS STANDARD
Minimum touch target size for reliable interaction
12.5mm
AUTOMOTIVE REALITY
Typical touch target size in current vehicles

Human factors research establishes 19mm as the minimum reliable touch target size for consistent interaction. Yet many automotive touchscreens use targets as small as 12.5mm4.

The Moving Context: Touch accuracy decreases significantly in moving vehicles due to vibration, acceleration, and the need to glance rather than stare at controls.

Color Coding Fails in Real Light

Color is a powerful design tool, but automotive HMI standards often ignore how real-world lighting conditions affect color perception.

Sunlight
COLOR WASH-OUT
Bright light reduces color contrast and discriminability
Shadows
COLOR DISTORTION
Dashboard shadows alter perceived colors
Night
BLUE LIGHT ISSUES
Blue displays cause eye strain and reduced acuity

SAE color standards for automotive displays don’t adequately account for how sunlight, shadows, and night driving conditions affect color perception5. This creates situations where safety-critical information becomes unreadable due to poor color choices.

The Evidence Gap: Aviation standards include extensive color visibility testing under various lighting conditions. Automotive standards largely ignore this critical factor.

Mental Models Don’t Match User Expectations

Perhaps the most fundamental HMI problem is that car interfaces follow aviation logic rather than everyday user mental models.

Aviation Logic
EXPERT MENTAL MODEL
Interfaces designed for trained specialists
User Logic
EVERYDAY EXPECTATIONS
How average people expect interfaces to work

Car interfaces often use aviation conventions that confuse average drivers. For example, multi-function controllers and nested menus follow cockpit design patterns that require extensive training to use effectively6.

The User-Centered Solution: Interfaces should match how people naturally think about and interact with vehicle systems, not how pilots control aircraft.

Designing for the Invisible Passenger

The “invisible passenger” represents the human user that automotive HMI design consistently ignores—the average driver who isn’t a pilot or astronaut.

The Design Imperative:

  • Match user capabilities — Design for average drivers, not aviation experts
  • Learn from other domains — Airport signage shows better ergonomics than automotive displays
  • Use voice effectively — Auditory information reduces stress and keeps eyes on road
  • Size touch targets properly — 19mm minimum for reliable interaction in motion
  • Test in real conditions — Color and visibility standards must account for actual driving environments
  • Follow user mental models — Interface logic should match how people naturally think

The challenge for automotive designers is creating interfaces that serve the invisible passenger—the human driver—rather than assuming aviation expertise.

References

  1. SAE International, 2018, “Surface Vehicle Recommended Practice J2364: Navigation and Route Guidance Function Accessibility While Driving,” SAE International. ↩︎

  2. International Air Transport Association (IATA), 2019, “Airport Signage Guide,” 7th Edition. ↩︎

  3. Yang, H., Hu, N., Jia, R., Zhang, X., Xie, X., Liu, X., and Chen, N., 2024, “How Does Driver Fatigue Monitor System Design Affect Carsharing Drivers? An Approach to the Quantification of Driver Mental Stress and Visual Attention,” Travel Behaviour and Society, 35, p. 100755. https://doi.org/10.1016/j.tbs.2024.100755. ↩︎

  4. Human Factors and Ergonomics Society, 2018, “Human Factors Engineering of Computer Workstations,” HFES-100-2007. ↩︎

  5. SAE International, 2016, “Surface Vehicle Recommended Practice J1757-2: Standard Metrology for Vehicular Displays,” SAE International. ↩︎

  6. Green, P., 2018, “Human Factors for Automotive User Interface Design,” in Handbook of Human Factors for Automated, Connected, and Intelligent Vehicles, D. Fisher, W. T. Nelson, and C. C. Liu, Eds. Boca Raton, FL: CRC Press. ↩︎