A human-machine interface (HMI) is an interface that allows us to interact with a digital system. No matter what HMI we design, we need to enable users to take advantage of all that a system offers.
For almost two decades, the personal computer was the first thing that came to mind when we heard about digital HMI. But the situation changed, and today HMI is an integral part of many devices we use daily — mobile phones, smartwatches, IoT devices, and even cars. Car HMI design is a relatively new field with specific challenges.
My team has experience designing for major automotive companies like Mercedes-Benz and Mitsubishi, and we want to share some of our practical experience in HMI car design.
What is HMI?
A car HMI is a collection of functional elements (such as head unit, instrument cluster, and head-up display (HUD), as well as interaction mediums (touch, voice, haptic) that can turn the vehicle into a living space.
A brief history of digital HMIs
Car makers initially introduced digital HMIs in the early 80s. At that time, the number of features in regular vehicles was rising rapidly. Designers needed to provide controls to allow drivers to manage these new functionalities.
They followed two different approaches: some of them used analog controls (they add a physical button for each feature), while others added a screen with dynamic content. The first approach was popular among German car manufacturers, while the second was popular among American and Japanese car manufacturers. The 1986 Buick Riviera is an early example of the latter approach. Inspired by aircraft design, it allowed users to control radio stations and climate using a monochromatic touchscreen display.
Another noticeable example is Nissan’s CUE-X Concept introduced in 1985. The system offered colored touch screens with nice graphics. As you can see, the design and location of functional controls are very similar to modern vehicles.
The modern HMI is a mix of a car control center and an entertainment system. It allows users to change climate settings, find a route to a particular destination, or watch YouTube videos.
Why did so many car manufacturers suddenly decide to introduce HMI displays in their vehicles?
Digital HMI just recently became a mass-market technology. Just a few years ago, HMI was a prerogative of luxury vehicles.
The primary reason for the change is money. It’s far easier to integrate a display in a cockpit and then update the software upon user feedback (similar to mobile phones) rather than to design a set of physical controls then have to redesign them entirely if something goes wrong.
Another reason is market expectations — users expect to see HMI in the car they purchase today.
But those are market reasons, what about human needs?
HMI has tremendous power to improve the user experience of drivers and passengers. Here are just a few areas where HMI can be valuable:
- HMI helps drivers make informed decisions. HMI can provide real-time data to users in an easy-to-consume manner. Take electric vehicles, for example. A driver can see the energy usage in real-time based on how hard they accelerate the vehicle.
- It can contribute to a safer driving experience. HMI can inform drivers about dangerous conditions such as when a vehicle is close to the lane limit, and prevent driving collisions by slowing down the car to avoid accidents.
- Further, HMI facilitates a more natural interaction between the driver and the car. HMI can establish a more natural interaction between humans and machines. For example, a voice-based system can allow drivers to use common words to command the car.
What to focus on when designing a digital HMI?
Based on my experience, designing a beautiful and effective HMI requires looking at artistry and functionality as one. These factors should be equal, working together perfectly for an immersive user experience.
Here are a few essential design principles I want to share with you:
1. Give users a sense of control
One of the 10 usability heuristics for UI design coined by Jakob Nielsen says, “The design should always keep users informed about what is going on, through appropriate feedback within a reasonable amount of time.”
This applies to any digital system, including HMI design for vehicles. HMI should always inform users about the current status through appropriate feedback within a reasonable time. It is especially important when a user is driving. Even when a car avoids an accident, it should inform the user what is happening (for example, by showing a visual alert with sound).
2. Follow a ‘safety first’ approach
The primary benefit of HMI systems is that they help us save lives. Modern cars are equipped with a lot of sensors and collect information, then use that information to track driving conditions. In a connected smart city, this helps monitor real-time situations and prevent traffic collisions and accidents. The system response to conditions can be:
- Reactive: The system informs the driver about what just happened, such as low tire pressure or microsleep (eyelids get heavy).
- Proactive: The system can analyze conditions, predict what might happen, and warn drivers about potentially harmful circumstances. For example, the system analyzes weather conditions and suggests users avoid taking a car on a day when roads will be icy.
The capabilities of HMI are rapidly evolving. Cars are becoming more intelligent and more capable of important real-time decision-making. But we’re a fair way off complete autonomy, and we’ll only see it eventuate through successful HMI.