Driving Performance Evaluation
of the AliScout Navigation System:
A Preliminary Analysis.

Paul Green, Jill Fleming, and Stewart Katz

May 1998

This paper describes the first of two experiments examining the safety and usability of the Siemens Ali-Scout navigation system, an in-vehicle interface that provides turn-by-turn visual and voice guidance. A total of 54 drivers varying in age drove an instrumented car to four destinations, twice using the Ali-Scout and, subsequently, once using experimenter verbal guidance. Subjects were tested in the afternoon, at rush hour, and in the evening. There were no crashes or near misses using the Ali-Scout, but there were four critical incidents where drivers changed lanes in response to navigation voice instructions without checking traffic. Excluding the turns into destinations, the turn error rate was 8 percent, and uncertainties occurred at an additional 13 percent of the turns. Most of the errors and uncertainties occurred in autonomous mode in which only the distance and direction to the destination were shown, not turn-by-turn guidance. Driving performance measures summarized in this paper include the mean speed while moving, and the standard deviations of throttle, speed, and lateral position. The first three of these measures were more sensitive to interface differences than the standard deviation of lateral position, a measure of lane variability. Generally, there were significant differences due to age, subject, destination, and section within destination for these measures. Subject differences were quite pronounced, with variability measures for the best and worst subject in each age-sex group differing by 2:1 to 3:1. The results suggest that the collection of variables sensitive to navigation interfaces is large, posing challenges for the development of a simple standard safety assessment.

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