As in-cabin interfaces evolve, the shift toward touchscreen-first design is being challenged by growing concerns around safety and usability. In this technical deep dive, Michael Nees explores the return of physical controls, examining what human factors research reveals about distraction, cognitive load, and how engineers can better balance safety, usability, and design in modern HMIs.
Written by
Michael Nees
Professor of Psychology
Why are physical buttons reappearing after years of touchscreen-first design?
Screens provide less meaningful feedback to our sense of touch, which means drivers spend more time with their eyes off of the road. We have to look at the screen to confirm that our fingers have located the desired function on the screen, then we must continue looking at the screen to receive visual feedback that the touch input was received. So physical buttons are reappearing as the evidence accumulates that touchscreens are a safety concern.
It’s also the case that research has begun to show that drivers want their physical controls back. Screens lack those satisfying physical textures that can guide your fingers without looking, and they lack the clicks that you can feel to let you know the control was activated. Â
What does human factors research say about distraction and cognitive load in modern HMIs?
The research has been fairly consistent in showing that touchscreens in vehicles are a problematic source of distraction. Requiring drivers to use touchscreens (versus physical buttons) for critical functions typically takes more time to activate the function, takes drivers’ eyes off of the road for longer, and leads to more erratic control of the vehicle while the touchscreen is being used. So touchscreens increase distraction and cognitive load, and distraction is a major contributor to accidents.
Where do touchscreens still make sense and where do they clearly fail?
Touchscreens may make sense for rarely used functions that typically are not engaged while the vehicle is moving. I can also envision touchscreen design choices that can help to mitigate potential safety concerns–things like locating the touchscreen near the driver’s line of sight, enlarging touch target areas, minimizing the depth of menus, and building clear haptic and visual feedback into the touchscreen design.
Still, I think the emerging consensus is that touchscreens clearly fail when they’re used for any function that is critical to the driving task and/or is used frequently. Controls that we need to use to drive safely and other controls that we use often while the vehicle is moving should be physical controls.Â
How do regulations and safety ratings influence interface design choices today?
I think most automakers pay a lot of attention to safety ratings. For consumers, research has shown that safety is one of the most important considerations in their vehicle purchase decisions. Research also has shown that safety ratings influence consumer behavior. So when Euro NCAP and ANCAP require physical controls for the highest safety ratings, I expect that most manufacturers will strive to design interfaces that can achieve those high ratings. Â
How should engineers balance usability, aesthetics, system integration, and other factors?
I think of these factors as a pyramid. At the base of the pyramid supporting everything else is safety. If you’ve designed a product that harms or kills someone today, then you’ve designed a failed product. The next layer of the pyramid is usability: can drivers access the interface efficiently and intuitively? Aesthetics is the top layer of the pyramid and occupies less space overall for me. I know it’s important that the product looks great and brings pleasure and satisfaction to the driver, but to me none of that matters if the product is not safe and usable first.
I know this is a bit reductive–usability can influence safety and so on. But I think the best balance is when teams of engineers, designers, and human factors experts work together collaboratively throughout the full design process, start to finish. There’s a long history of engineering failures that resulted from ignoring human factors until something goes wrong.Â
