The present study sheds some light on two questions: How can safety be measured, and how should the human-machine interface of in-vehicle information systems be designed? As to the first issue, it turns out that subjective measures were far more sensitive to what happened when the driver was using the in-vehicle information system than were the objective measures of driving. Subjective ratings that showed the clearest effects, at least in the most demanding task condition (i.e., the filter condition), were the ones on course keeping and (anticipating) braking and decelerating. Ratings on the other scales also showed effects of the in-vehicle tasks, but not as consistently across the various situations. Of the objective measures, only steering frequency at straight inner-city roads increased with filter programming, and participants tended to look less to the right at general rule intersections. The other measures listed in Table 2.11.3 appeared not to be sensitive measures for reductions in driving safety. The fact that increased steering frequency coincided with reduced safety ratings on the straight road segments suggests that steering frequency is an indicator for safety reductions in such situations.
Abstract