Edited by Rick DeMeis
Part 1 of this article discussed the nature of driver distraction and rules for intuitive HMIs.
Simulation of 'physical' objectstactile feedback
The more intuitive the HMI interface, the less time it takes for the user to use it, directly reducing driver distraction. A nonintuitive HMI, on the other hand, can cause distraction even after the driver has been trained to use it.
If the interface mimics items in the physical world, it can allow the driver to use the system quickly, without looking. Consider, for example, haptic (or active tactile) feedback. A knob can pulse under the user's fingertips, presenting virtual detents as the user scrolls through items in a list. A knob could also increase rotational resistance when reaching boundary edges, giving a non-visual clue as to the location of a setting within the total range. Haptic touch screens, meanwhile, can mimic the feel of actual buttons, allowing the user to get sensory feedback on a selection without requiring an extra glance.
Devices such as the iPhone allow users to scroll through selections by means of a "point and flick" interface. Such interfaces emulate the feeling of manipulating a physical object by introducing "friction" to slow down the scrolling action and a "bounce" to indicate that the user has hit the top or bottom of the list.
A touchscreen display with an iPhone-type "point and flick" interface. Dragging your finger grabs and imparts momentum to the list content (indicated by small hand cursor).
Displays that gradually scroll from one selection to the next, as opposed to instantly popping each selection into view, also give a better sense of physicality, making it easier for the user to control and understand the motion.
Meanwhile, shadows and reflections on graphical images convey texture and substance, giving an impression of reality that can make interaction with the controls easier or more obvious.
Audible clues, such as clicks on button selections, or swishes when fading from one screen to another, can also inform users of their actions, without forcing them to steal an additional glance at the display.
Flexible display advantages
An LCD panel can be programmed to show any graphic, yet designers often retain fixed locations and interfaces. The ability to convey the relative importance of information through size, color, transparency, shape, or motion is rarely utilized. For instance, in a digital instrument cluster, the speedometer could gradually change the color or increase the size of the current speed digits as the driver approaches or exceeds the speed limit.
By displaying the current speed limit (acquired from the navigation database), a digital instrument cluster can help the driver notice excessive speeding and slow down to safer speeds.
Similarly, gauges like battery voltage or oil pressure could fade or become smaller when in a normal functioning range, so as to provide less distraction from more important information.
By fading out gauges that display normal operating ranges, a digital instrument cluster can help the driver focus on the task of driving.