In automotive use, HUD is used to project relevant information directly within the driver's forward view, thus allowing them to keep their eyes on the road. While the technology is complicated, the science is rather simple - light from a projector, usually recessed at the top of the dashboard, reflects off a special portion of the front windshield. Most of today's systems display vehicle speed, engine speed, navigation information and warnings.
The technology isn't without fault, however. Since it is reflection-based, drivers wearing polarized sunglasses have a difficult time seeing the image. And, like most newer electronic innovations, pricing is still an issue. Analysts currently estimate that the cost adds about $1,000 to the price of a high-end infotainment system, but those figures will fall as the HUD gains market share.