For a long time I have wondered how the teams that design car stereos can fail so miserably at making car stereos easy to use. The function of a car stereo is not complicated, and there are few tasks that need to be considered in the design of a car stereo interface. Approximately in order of importance these tasks are;

  1. lower the volume
  2. kill the sound
  3. raise the volume
  4. select the source (e.g. FM, AM, CD, Auxiliary)
  5. skip tracks
  6. change the frequency

It doesn’t take much guerilla usability testing to find that almost no one uses any of the advanced features manufacturers try to pack into car stereos – let alone understand them or take the time to configure them!

  • Equalizer
  • Radio presets
  • Time
  • Selecting display data; Track time, time remaining, time of day, frequency
  • Plus a myriad of other functions that are so unimportant even I – a rather exploratory user – didn’t even try them or found them so useless I’ve forgotten them already.

I recently found a manufacturer that seems to have made a significant improvement in the interface design of their car stereo; Honda. This photo is from a fairly recent model of a Honda Jazz;

Honda Jazz car stereo is designed for Usability

Since the most important tasks are all related to the volume, the volume dial is big. IMHO it should be even bigger. And turning the volume button all the way down should turn off the stereo. An explicit ‘press’ on the volume dial or any other button is redundant. How often have you discovered the car stereo has been left on but the volume was all the way down?

Multi-function volume dials are also error-prone. Our car stereo has a small fiddly dial that requires a lot of attention to find and turn. I usually accidentally bump it when I try to change the volume and it goes into equalizer mode. Then I have to either press it a few more times to get it back to volume mode, watching for it to get there (which is dangerous, considering I’m usually driving a vehicle!), or wait for it to time out – possibly at the cost of a phone call, a conversation or an important signaling sound!

The Jazz’s car stereo is not nearly as bad as our car stereo, but removing the press-to-power-off functionality would simplify the system and make it less error-prone.

Honda has correctly positioned the volume dial on the driver’s side of the stereo (cars in NZ are right-hand drive for left-hand-side roads). Most stereos here are laid-out for american consumers and require the driver reach further to adjust the volume – endangering the lives and safety of the operator and passengers.

The buttons around the dial are positioned for proximity to the dial. However they are so close that it is also easy to bump them in a moving car. They are also not optimised for read-ability. If they were oriented horizontally it would be easier to read the labels to find the sought button. The circular orientation does however facilitate recall and memorization.

The Jazz’s stereo also correctly separates the tuner (frequency-changing buttons) from the track-skip buttons. User’s mental models do not always associate the similarity of these two functions and dual-labeling always makes an interface more work than it needs to be. The up-down lever type button also confirms the function of these buttons and the fact that up/next is the opposite of down/previous.

The Jazz’s stereo does have a few additional buttons and features – but it’s feature-set is severely restricted compared to most car stereos I have encountered – and this is a superb thing! Car stereo designers need to take some lessons from the rigor and discipline of airplane interface designers. Cars are dangerous and interfaces that are difficult or distracting augment that danger.