Verbal aids to automobile navigation: The impact of directional instructions on drivers' behaviour at the approach of intersections

Recent innovations in microcomputer and display technology have resulted in sophisticated route guidance systems that help drivers in selecting and ma intaining routes. However, the efficacy of these systems still depends on t he drivers' cognitive characteristics. These characteristics imply constrai nts on what kind of information drivers need and how such information can b e best displayed. In general, it is recognised that voice guidance makes th e driving task easier and safer. In particular, drivers need guiding inform ation before every required rum. The most obvious criterion of effectivenes s of guiding information is the rime left available before the maneuver. Us ing the driving simulator SHERPA, we tested the influence of time to maneuv er on automobile drivers' behaviour at the approach of two reorientation in tersections. We designed four conditions of verbal announcements involving various degrees of anticipation with respect to the locations where the dir ectional changes should occur. We intended to identify the announcements al lowing for the mast appropriate anticipatory behaviour with the lowest risk of accident. Behavioural measures included velocity, pressure on the brake and the clutch, acceleration of the steering wheel, and position of hands on the steering wheel. The results showed that two of the four-conditions d id not allow drivers to anticipate their actions in the intersection and re sulted in dangerous behaviour. The other two, which approximated informatio n deliverance by road signs, allowed drivers to anticipate more effectively . However, none of the latter announcements taken separately were really op timal. In one case, the drivers tended to forget information, while in the other, the announcements failed to provide confirmation of previously memor ised instructions. A combination of types of announcements should thus be r ecommended. Based on the results of this investigation, we propose specific ations that designers might use to develop an effective and safe guidance s ystem.