Simplicity trumps sophistication with automotive HMI

Automakers must select the right design principles for automotive displays, or risk new levels of distracted driving. By Chris Rockwell and Mark Palmer

It appears larger car displays are inevitable. Mercedes-Benz attracted significant attention at the 2021 CES with its new MBUX Hyperscreen, a full width dashboard display, and almost all future concept vehicles have their own versions of super-wide high-definition displays, combined with extensive head up displays (HUDs).

Special report: Automotive HMI

Although many consumers are excited by how these bigger displays look in the car, there are real concerns that they will increase driver distraction. Larger and more distributed displays have the potential to create a better and safer driving experience, but it will require the right design principles to accomplish this.

A technology-centred approach to design typically starts by proving a technology—such as a full width display—is possible before necessarily thinking about how it’s really going to impact the user. In contrast, a user-centred design process starts with experiences and then leverages technology to provide for user needs. A foundational understanding of how people think, act, and feel is crucial for creating the right solutions.

Mercedes MBUX Hyperscreen
In-vehicle displays are getting bigger, showing more information than ever before (Pictured: MBUX Hyperscreen)

Just as brilliant engineers and designers can create cutting-edge technologies, brilliant social scientists have made groundbreaking discoveries about how humans experience the world. Studies in sensation and perception have led to important theories like selective attention, situational awareness, signal detection theory and inattentional blindness, providing insights about how people see and interact with the world around them.

Most people are surprised to find out that we don’t view the world like a video or photograph, but instead “sample” parts of the scene and let our minds fill in the blanks based on what we are focused on—or distracted by. The famous “Invisible Gorilla” test illustrates just how incomplete our perceptions can be. The test shows how, when focused deeply on one activity, it can be easy to disregard other things going on in the surrounding environment.

Applying this thinking to in-vehicle displays, the potential opportunities and pitfalls for their design become clear. What is shown on displays becomes part of the world the driver sees (or fails to see). When information is projected on the windscreen, does that get “sampled” while a nearby pedestrian goes unnoticed? When a text alert pops up in the cluster, does the driver notice the dog in the road? Do redundant visual cues on displays take attention away from other important things?

The collaboration of forward-thinking engineers, designers and social scientists holds the key to designing displays that will lead to safer, more satisfying driving experiences

Lextant recently conducted a review of an augmented reality display in which five different arrows in the visual field all point where to turn. It revealed that as visual fields become more complex, it is harder to notice important information. The collaboration of forward-thinking engineers, designers and social scientists holds the key to designing displays that will lead to safer, more satisfying driving experiences.

Lextant has focused and simplified user-centred design insights into the following “Right Design” principles that should be applied to display design. 

The right information

All information in front of a driver is competing for attention. Some information is more important than others and care should be taken to prioritise the most critical. Primary information is used to drive the car safely and effectively. Secondary information describes practically everything else like climate settings or media. Primary information should take priority during driving, and the information needs to be easily understood. Secondary information should not interfere with primary.

The right time

Not all information is necessary at all times, but some information is critical at certain times. To avoid information overload, displays should only present information that is important to the driver exactly when it is needed. Smart systems using artificial intelligence can predict when the driver needs specific information and present it to them at the right moment.

The right location

To date, cars have included a display behind the steering wheel, a display in the centre of the dash, and some limited heads-up display (HUD) on the windscreen. More and bigger displays allow information to be distributed around the car interior. The placement of information can either increase or decrease mental workload.

To decrease workload, displays can create consistent zones where presented information makes intuitive sense. Adding redundant auditory and haptic information can further reduce workload. Careful placement of relevant information can greatly increase usefulness and usability. If the driver needs to search for information, mental workload—and distraction—will increase.

"As part of this innovative project, we have been engaging with the insurance sector to help them understand the evidence they require to adapt their business and insurance pricing models when underwriting connected and automated vehicle (CAV) trials, in readiness for commercial deployment of CAVs at
Designers might prefer functions to be embedded in sleek touchscreens; engineers would opt for physical buttons in many cases

The right format

The most useful information allows the driver to take immediate action. The less a driver has to interpret, translate, manipulate, and transform information, the faster that information becomes useful, and the quicker they can react. An HUD can distract the driver with text or inform them if it visually connects to the environment, for example by “painting” a lane during navigation. Displays can reduce the amount of mental workload required of the driver by providing information in a format that requires little to no thinking.

The right amount

The design principle of ‘less is more’ is critical for a safe driving experience, and the larger the display area, the harder it is to follow. When automakers show large, full width HD displays in cars, they tend to fill them up with as much content as they can. While this shows well, it does pose driver risks. The more information presented at any one time will increase the amount of time the driver has to search for it. Visual searching equals distraction.

The right circumstance

Driver monitoring systems (DMS) are designed to track driver behaviours during certain circumstances. This “protective” innovation is important because drivers can fail to understand their collaborative role when engaging with various autonomous drive modes.

For instance, the Mercedes-Benz Hyperscreen includes a passenger display, which understandably has numerous entertainment choices. To prevent the driver from being distracted, the system monitors the driver to see if they are looking at the passenger display. If they are, it shuts off. Larger, distributed displays will need to be smart enough to present information based on context and circumstance.

Automotive manufacturers can unleash the potential of displays to create safe driving experiences by showing restraint in how they add detail and information

Interacting with displays

There are many ways to interact with in-vehicle displays. Touchscreens, physical controls, steering wheel controls, voice recognition, and hand gesture input all have advantages and disadvantages. Compelling concept cars typically rely on touchscreens, voice, and mid-air gestural input to keep a clean looking, hi-tech and minimal design. However, human factors engineers will focus on large shape-coded physical controls to ease mental workload. It is important that experts collaborate to create designs that have the appeal of hi-tech with an understanding of users’ strengths and weaknesses.

Revered architect Ludwig Mies van der Rohe crafted the dictum “less is more,” as an appeal to modernist design and architecture, and this holds up well today. Years later, designer Deiter Rams elaborated on that principle by declaring that good design is like a good English butler: they’re there for you when you need them, but in the background at all other times. Automakers can unleash the potential of displays to create safe driving experiences by showing restraint in how they add detail and information to what is already a rich and complex environment.


About the authors: Chris Rockwell is Founder and Chief Executive of human experience consultancy Lextant; Mark Palmer is Chief Operating Officer at Lextant

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