Two automotive designs
I recently drove two different Toyota cars. One was Prius and the other a Highlander, both hybrid vehicles, but it is their usability rather than their fuel consumption that we will examine here.

The dashboard controls on each model were quite different. The Prius has a graphical touchscreen which included a sat-nav system, while the Highlander has a more conventional set of controls with physical dials and buttons dedicated to each task.

I will not try to make a judgement on which was better, since they achieved very different aims. Advanced features such as sat-nav, which are very graphical in nature, could never have been implemented on the Highlander's dash, so the comparison would be fairly meaningless. Instead I am going to focus on one feature that was very different on each; examining those differences will teach us a couple of things to watch out for in our own design.

I was driving these cars in sunny southern California, so the air conditioning was on and needed frequent adjustment. There were two settings: a temperature and fan speed. The Prius allowed control through the touchscreen, while the Highlander has two dials, one for temperature and one for fan speed (Figure 3).

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After a week in each car, there was no doubt in my mind that the dials made control far easier. The old-fashioned low-tech method out-performed the sophisticated GUI by a mile. Let's look at the reasons why.

First of all the mechanical dials were always in the same spot. You just put out your hand, and you could find them without looking. On the Prius there was an off-screen "Climate" button that you pressed first, and then you had to select the fan speed using an onscreen button, if that is the item you wanted to adjust. So in terms of navigating the GUI, the Prius forced you to do some work before you even got to the setting you wanted to change.

This difference is a fairly inevitable consequence of designing the controls in a GUI--you can fit far more functionality in a smaller space, but the compromise is that you have to navigate to some of those features. It does make me wonder if the Prius should perhaps have taken a few of the most frequently used features out of the GUI and given them dedicated controls.

Of course, there will always be a cost trade-off here. Part of the motivation for designing with a GUI is to get rid of all of the other dials and buttons to save cost--just remember that the cost is not just in money, but sometimes the cost is in usability, too.