An empirical study to determine guidelines for optimum timing of route guidance instructions

For a route guidance system to be acceptable to drivers it must meet their expectations, based on their previous navigation experience. Also, the system output to the driver should be designed in such a way as to maintain or improve current levels of safety. Most certainly, it must not be detrimental to safe driving as a result of driver distraction, lack of confidence or erratic vehicle control. The topic of this investigation-the appropriate timing of a route guidance instruction-is critical to system acceptability and safety. If an instruction is given too early, the driver is likely to forget the information whilst attending to other driving tasks. If the instruction is given to late, it will either cause the driver to brake suddenly or to maintain safe driving but miss the manoeuvre completely. The authors describe a study carried out to identify the factors which may affect timing and, to select those which were the most important, those which current/future systems could detect/measure and those which the current study could control, select for or measure