Timing of Auditory Route-Guidance Instructions
(UMTRI-95-6)

Kellie George, Paul Green, and Jill Fleming

June, 1995

This experiment examined how far from an intersection an auditory route guidance system should present the final turn instructions ("Turn right"). In part 1, 48 drivers followed instructions from a simulated speech-based, in-vehicle navigation system ("In approximately 2 miles, turn right at the traffic signal."), responding "Is this it?" when they thought they had reached the desired intersection. In response, the computer gave the appropriate guidance ("no, continue..." or "turn..."). In part 2, they repeatedly approached two different intersections, with feedback from previous trials ("too far," "too close," "OK") being used to adjust when messages ("turn left") were given.

The method used in part 1 was much more efficient than the method used in part 2. Desired presentation distances in part 1 averaged 450 ft (when approached at 40 mi/h), approximately 50 ft greater than those obtained in part 2 (where intersections were more familiar). Desired presentation distances are best estimated from the part 1 data:

Distance (ft) = -389 + 119 (Age.code) - 113 (Sex.code) + 95 (Turn.code)
+15 (Speed in mi/h) + 21 (# Vehicles Ahead).

where: Age.code 1= (18-30 years), 2 = (40-55), 3= (65-80)
Sex.code 1= women, 2 = men
Turn code 1= right, 2 = left

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