In the design of Lane Departure Warning Systems (LDWS), it is necessary to determine thewarning timing that does not only ensure the effectiveness of the warning but also reduce theannoyance of the warning. Concerning the relation between the warning timing and theeffectiveness of the warning, we have reported the performance of the steering avoidance byan experimental study using a driving simulator (1). The results showed that it is necessary tokeep the time margin longer than 0.9 s for the successful avoidance of lane departure. Thispaper mainly describes the latter point regarding the relation between the warning timing andthe annoyance. We have investigated Time to Departure (2) that means the predicted timemargin before the lane departure, when 10 drivers drove a passenger vehicle on 5 kinds ofJapanese highways in a metropolitan area. The results show that the accumulated frequencyof Time to Departure at 1.0 s is approximately 0.5 percentile, in terms of the frequencydistribution of Time to Departure. This means that the frequency of time margin less than 1.0s is equal to 0.5 percent in the total driving time. Further analysis concerning the relationbetween the frequency of warning output and the annoyance might be necessary. But, it canbe seen from the investigations that the annoyance will be reduced when the warning timing isset at 1.0 s of Time to Departure, since the frequency of the warning output will besubstantially small under normal driving conditions. We regard that these experimentalresults can be useful for designing the warning timing of LDWS.
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