Car interfaces and usability

When car designers incorporated more gadgets into car cabins, they came up with things like BMW's iDrive, Audi's MMI, and Mercedes-Benz's COMAND. Their interfaces received heavy criticism from an automotive press that was resistant to change. But the problems went beyond Luddite journalists, with the designs of these systems partially to blame.

Car controls remained basically the same for 100 years--you have a steering wheel, accelerator pedal, brake pedal, and some type of transmission control. Car designers haven't had to deviate from that same basic setup, so maybe it's understandable that interface designs for car systems often lack basic usability.

As the Web grew in the 1990s, a lot of thought was put into usability issues. Jakob Nielson influenced Web builders with his basic principles of usability for Web design. They are:

• Learnability: How easy is it for users to accomplish basic tasks the first time they encounter the design?
• Efficiency: Once users have learned the design, how quickly can they perform tasks?
• Memorability: When users return to the design after a period of not using it, how easily can they reestablish proficiency?
• Errors: How many errors do users make, how severe are these errors, and how easily can they recover from the errors?
• Satisfaction: How pleasant is it to use the design?

These principles can also be applied to car interfaces, and they become much more important in an automotive venue, as bad interfaces can lead to accidents. I'm going to go over the major systems in use today, and critique them with these usability principles. The car interfaces comprise the hardware and software elements.

iDrive
BMW was a pioneer in developing its unified interface, making it subject to more criticism. In early iterations of iDrive, BMW removed all duplicate controls, forcing the driver to use a single push-button/joystick/knob to control the onscreen software interface, a classic example of engineering arrogance. As a result of criticism, BMW restored some controls that people are used to using and added a back button to iDrive.

I don't think iDrive deserved all the criticism it got, but it deserved some. Although the hardware part of it works well, I've never liked the feel of its soft clicks and stop points. The functional problem mostly comes from the software interface. It lacks Nielsen's Learnability principle, as it's often difficult to figure out if you should be turning the knob, moving it like a joystick, or pushing it like a button to select onscreen menu items. Because of its Learnability problems, many people got frustrated with iDrive and just didn't want to use it.

However, iDrive is pretty efficient, Nielsen's second principle. Once I gained some expertise after using it in multiple cars, I could set destinations in the navigation or make calls through the Bluetooth interface quickly. Concerning Nielsen's Errors principle, I found that was tied in with the learning curve--as I got more used to iDrive, I would make fewer errors.

Multimedia Interface (MMI)
One of the first interfaces we saw at CNET Car Tech and liked was Audi's MMI. This system uses a knob surrounded by four buttons to control onscreen menus. MMI is easy to learn, partly due to a software interface that works well with the hardware. Once you realize that the buttons surrounding the knob activate the quadrants on the screen, you can easily access the car's navigation, stereo, cell phone integration, and other systems. It also does well on Nielsen's Memorability principle, as I've found no problem adapting to it in different Audis that we test, even when the MMI knob moves from the console to the dashboard.

But MMI falls apart on the Efficiency principle. Mirroring the button arrangement on the screen works, but Audi also mirrored the knob too closely on many of the screens. For example, you use an onscreen rotary dial, which matches the movement of the hardware knob, to select letters in city and street names when setting destinations. Rotary dials are extremely tedious to use--it would have worked better if the letters were lined up in a row. It might require the same amount of knob twisting to enter an address, but it just seems easier. Likewise, there is an audio controller screen that shows a rotary control knob, again matched by the movements of the hardware knob, which lets you skip CD tracks forward or backwards. It looks neat, but in practice, there's no reason to use it, as another screen shows you the track list, letting you go right to the track you want.

One thing I liked about the latest iteration of MMI, as seen on the 2007 Audi A6, is that it uses different colors for different car systems. Blue is for navigation, green is for cell phone integration, and orange is for the stereo.

COckpit Management And Navigation Device (COMAND)
Mercedes-Benz really stretched to get its COMAND acronym, but the system is probably the best of these three. At least, that is, when it uses a metal knob on the console, as in the higher-end cars. The cheaper Mercedes-Benz models get dashboard modules with an ugly plastic four-way button. The higher-end metal knob is very similar in its hardware to iDrive, with the knob also acting as a push-button and joystick. But COMAND is more easily learned than iDrive due to its software. Instead of trying to get particularly clever, the menus in COMAND use a linear menu-style layout. The screen shows the major car systems (navigation, cell phone, and stereo) as labels in a band at the stop of the screen. Turning the knob highlights each menu in turn, and pushing the knob selects that function. I took to it right away in the Mercedes-Benz CL550.

It's not perfect, though--the deeper you go in the menus, the more you are likely to make a mistake by, for example, turning the knob when you should push it like a joystick. But it is just as efficient as iDrive, letting you select letters for street and city names off of a horizontal band. COMAND also has the best-looking screens and the nicest-feeling controller among these integrated systems.

The real winner
Although not very elegant, the most usable interfaces I've seen are touch screen LCDs. Most touch screen LCDs appear in American and Japanese brands. Unlike trying to match the movements of a hardware knob with onscreen menus, touch screens have onscreen buttons that you can push. There is virtually no learning curve. If you want to enter a destination into the navigation system, just push the button labeled "Destination entry." These systems usually have hard buttons along the sides of the screen, but these are usually just to select the car system you want to control and are labeled as such.

With a touch screen LCD, it all comes down to software design. I've seen some more usable than others, but ultimately they have all been more usable than iDrive, COMAND, or MMI. For example, when entering an address, you merely have to touch the appropriate letter on the screen, which is much more efficient than selecting letters with a knob, which reminds me of using the minimal buttons on a video game to enter my initials next to my score.

The only drawback with a touch screen is that you have to be able to reach it. If the dashboard slopes away out of arm's reach of the driver, then you have to rely on a remote system like iDrive.