Although originally developed for aircraft use, headup displays (HUDs) have recently found application in automobiles. It is projected that there will be two major categories of HUD applications in the 21st century, based on a consideration of technological progress in associated hardware and the implementation of road-vehicle communications infrastructure. The first will be as an interactive display system that improves both operating ease and display legibility. The second will be as a navigation system capable of giving drivers at large quantity of complex information efficiently and safely.

This paper discusses the effectiveness of HUDs in these two major applications based on the results of preliminary visual-optical experiments. It is shown that drivers can receive some critical or emergency information from their effective forward field of view while looking at a HUD, when the angle of depression of the display is small. The use of HUDs as interactive display systems can capitalize on the small angle of depression that is one of the advantages of Lhe HUD design. A new HUD sysiem for navigation use is also proposed. Other advantages of HUDs include the long distance to the displayed image and the ability to superimpose the displayed information on the foward view in a compaiiblc manner. The use of HUDs in navigation systems can effectively exploit these advantages. It is thought that a navigation system built around a HUD could contribute to enhanced driving safety, because drivers need not divert their attention from the road in order to see the displayed information.