Driver distraction, which is one form of inattention, is a leading factor of vehicle crashes and near-crashes. Distraction occurs when a driver's recognition of information needed to safely accomplish his driving task is delayed because some event, activity, object, or person within or outside the vehicle induces or shifts his attention away from the driving task. To measure the distraction, driving performance indexes are commonly used. However, we employed biological signals to directly and quantitatively measure the distraction. Our experiment results identified such useful biological indexes as EEG's total power spectrum, beta wave ratio, ECG's heart rate, and its LF/HF. In this article, we introduce our trial in which we applied the index candidates to assess the information display positions.