The data were used to compare features of navigation system interfaces in terms of their support of drivers' needs for guidance and contribution to safe driving. Certain design principles (which apply while driving, not necessarily for trip planning) emerge from these analyses.
Contextual guidance information on a screen display (including landmarks and other orientation cues) is potentially helpful, provided it is automatic, or system driven. However, the potentially greater allocation of visual attention to the display increases the risk of insufficient attention being directed to the road.
Voice guidance, with context-rich information, and without additional or concurrent visual information, is more effective than displaying guidance information on a visual screen.
Automatic Voice guidance appears to be the most effective and safest. Possible explanations for the superiority of the automatic voice system are that the system can better anticipate upcoming decision points because it "knows" the road network, it frees drivers from having to decide and initiate interactions, and it causes drivers to drive at a pace established by the system. There is growing evidence that voice instructions with a redundant screen display is the optimal configuration for a navigation interface ( Parkes & Burnett, 1993; Verwey, 1993). Indeed, the Ideal Navigator condition (i.e., automatic voice messages and a redundant visual display) produced the best QOD scores.
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