Head-up displays, once confined to sports cars and luxury vehicles, are starting to penetrate the mass market.
This year, 38 vehicle models available in the United States have standard or optional head-up displays, according to Edmunds.com, up from 13 models five years ago.
Automakers regard the displays as useful for showing navigation routes, audio channels and other infotainment data while allowing motorists to keep their eyes on the road.
The displays project light onto the windshield, creating an image that appears just above the hood about five to eight feet beyond the windshield.
Early-generation displays "were one color, with very basic information," said Ron Montoya, an analyst with Edmunds.com. "They reminded you of a digital alarm clock. Now you can get more color and more graphics."
For instance, new displays can overlay a turn arrow on a street ahead, showing drivers exactly where to turn to find a destination.
"The technology is getting better and the prices have come down," Montoya said.
Audi, BMW, Lexus and Cadillac account for most of the models sold with head-up units in the United States. Mercedes-Benz, previously a holdout, is expected to make head-up displays available on its C-class and S-class models this fall.
Now that automakers are racing to upgrade their infotainment displays, top suppliers view head-up technology as a must-have.
Nippon Seiki, Harman, Denso, Continental, Visteon, Bosch, Panasonic, Delphi and other suppliers are marketing head-up displays. But all are struggling to solve some nagging technology problems.
Head-up displays require specially treated windshields. Bulky optical equipment is needed to produce the image, and the optics box generates considerable heat.
Suppliers are solving those problems gradually with each new generation of equipment.
During the Detroit auto show, Panasonic unveiled a head-up unit that produces an image 16 inches wide by 6 inches high. That's roughly twice the size of most current head-up images.
Panasonic and other suppliers are racing to develop larger head-up images for "augmented reality" displays. Some possible uses might include highlighted lane markings in bad weather, visual warning symbols for road obstructions and turn-by-turn arrows.
One big problem with augmented reality displays is the sheer size of the optics box needed to create the images. Panasonic claims its optics package is half the size of rival units.
To keep costs down, automakers could pair a head-up display with a digital instrument cluster, then eliminate the center console screen, says James Grace, Panasonic's director of advanced engineering.
This approach could win favor at a time when some automakers are questioning the need for the console screen. The Audi Allroad Shooting Brake concept debuted at the Detroit auto show without a console screen. Instead, all navigation and infotainment data are displayed on the car's digital instrument panel.
While the Shooting Brake also lacked a head-up display, Grace and other supplier executives say a head-up unit would mesh nicely with a digital instrument cluster.
"If you take the center stack away, you can have a cost-neutral" head-up unit, Grace said. "I doubt that Audi will be the only company" that dispenses with a center screen. "People are thinking in similar ways."
To further cut costs, some automakers are adopting "combiner" head-up displays that show images on a small transparent plastic pane mounted on the dashboard.
Combiner head-up displays are cheaper and much more compact than "projector" displays and thus are better suited for smaller vehicles. Moreover, they don't require specially treated windshields.
On the downside, they don't match the image quality of more costly projector displays.
The Mazda3 and Mini Cooper use combiner displays to project vehicle speed, turn-by-turn directions and collision warnings.
By 2020, combiner displays will account for 60 percent of head-up displays sold worldwide, predicts Mark Boyadjis, an IHS Automotive analyst.
Overall, IHS forecasts global sales of 9.1 million head-up displays by 2020, up from 500,000 units this year.
Combiner displays "are going to be the drivers of growth in the overall HUD market," Boyadjis said. "Because they cost less, you can package them with other options."
So where is head-up display technology going? Over the next two or three years, we're likely to see augmented reality displays in luxury models. But the real growth is likely to occur at the mass-market level with simpler, less costly combiner displays, predicts Johann Hiebl, chief of Continental AG's infotainment unit.
"Cost is still a major issue -- even in the luxury market," Hiebl said. "If the [cost] is too high, the option rates remain low."
Hiebl doesn't expect a sudden breakthrough that would allow automakers to cover their windshields with virtual displays. But the technology will improve with each new generation.
"It's a step-by-step improvement," Hiebl said. "This is the way we see things going."