Life with a digital speedometer

In my cognitive psychology class and on this blog, I have criticized the digital speedometer as not being as instantly useful as an analog speedometer, where you can quickly judge the angle of the needle and get a sense of how fast you are driving. However, buying a car is surprisingly emotional, and cognitive design principles can get thrown out of the window. In short: I bought a 2008 Honda Civic, and I’ve been driving it for about a week. How’s the digital speedometer?

It’s… usable. I don’t think it’s better than an analog speedometer. I can glance down and read the number, and interpreting my speed does not really take that much longer than an analog display. So I can get along just fine with it.

I do, however, take issue with why Honda made the change (source: Honda Press Release for the 2006 Civics, PDF version):

And they state the reason clearly again in the same press release:

The two-tier instrument panel positions priority gauges like the speedometer up high in the driver’s field of vision.

So Honda wanted to put the speedometer - critical information, to be sure - closer to the driver’s field of view. It’s a valid design choice, but why not move the analog speedometer upwards? My guess is that a traditional circular analog display would have been too large and would have interfered with driving. Therefore, as a compromise, Honda made the speedometer digital to save space. It doesn’t take up as much space as an analog version, and it has the benefit of looking pretty cool.

The problem with this is twofold. The first problem is that our peripheral vision is really poor. Our sharpest vision is only 1 degree of visual angle (the width of your thumb an arm’s length away is 1-2 degrees). Everything outside of that area is not very sharp. We can get some information out of it - maybe the angle of a line (analog speedometer) - but reading (digital speedometer) gets fuzzy. So Honda put the display closer to the driver’s field of vision, but made it more difficult to read by going digital. To make matters worse, there’s a concept called the Useful Field of View (Ball et al., 1988). Essentially, the more focused we have to be at a central task, the less we can pay attention to peripheral objects and events. Driving is an attention-heavy task, so we have even less attention to take in information in the periphery.

The end result? I still have to move my eyes away from the road and down in order to read my speed. Moving critical information closer to the driver’s visual field is good idea, but the implementation failed because of lack of knowledge about vision and cognition. By not understanding peripheral vision or the effects of attention to a central task, the repositioned digital speedometer fails at its goal of being better. It’s not a bad design, per se, but it does not improve the driving experience.