names were obtained from the navigation system, whereas road sign information was obtained from the road and traffic infrastructure. For drivers who were familiar with Tokyo, most street names were also obtained from the road infrastructure. It is usually easier to identify intersection names on the road because the signs showing their names are attached to highly visible traffic lights, whereas not all intersection names were displayed by the navigation systems. The same was true for road signs; they were fixed above streets and easily seen by drivers, but the navigation systems used here did not show road signs on the display. On the other hand, although street names were displayed on the navigation system's display, the panels showing the street names were sometimes difficult to see from the car because the drivers did not know their location or because heavy traffic hid the panels. The difference in the frequency of use of street and intersection names between the navigation system and the road environment may be due to inconsistencies between the information displayed by the navigation system and that of the road environment. The use of navigation systems could be facilitated by ensuring that street names are easily seen, which is the responsibility of the administrators at the ministry or the metropolis. Whenever possible, navigation systems should display road sign information and intersection names in the same location as the actual signs in the road environment. Unlike the names of streets and intersections, structures are arbitrarily chosen by drivers as landmarks; therefore, the interface should show structures that are likely to be useful as landmarks (i.e., that have all the characteristics already described). The information on the navigation system should also be updated to reflect changes in the road and traffic environment.
Comparisons of the frequency of word use showed several differences between the familiar and unfamiliar driver groups. Both the navigation system's interface and the road traffic infrastructure should be designed to facilitate navigation by unfamiliar drivers. For example, the signs for place names should be clearly visible in order to help unfamiliar drivers to identify the place. A small number of subjects were used in this experiment, thus further analysis of a large number of subjects would be necessary to confirm the effects of familiarity on navigation.
Subjects often used the navigation system in order to identify where to turn. Commonly used landmarks included buildings, street names, intersection names, distances, place names, and road signs. In order to make using navigation systems more efficient, the signs showing street names should be clearly visible and intersection names and road signs should be