The aim of this study was to propose an effective method for displaying driving environment and properly transmitting this to drivers. The display was designed by changing two types of proximity, that is, the proximity of the display and the proximity of the task itself. The proximity of the display was controlled as the type of the display or the distance between two displays. The proximity of the task was controlled as the difference of two tasks performed on the two displays. The participants (a total of eight graduate or undergraduate students) were required to carry out simultaneously a main simulated driving task and secondary tasks controlled by the two proximity factors above. The secondary tasks were one of the followings: reaction task to the approach of a following vehicle, lane changing task, reaction task when the distance to a destination is within the predetermined distance, and speed maintaining task. As a result, it has been demonstrated that the performance under the dual task condition does not always obey the predicted result by proximity compatibility principle.