TOKYO—When selling car navigation systems, Japanese retailer Autobacs touts a special add-on: kits that convert the mapping gadgets into televisions, so drivers can watch their favorite shows.

"Even While Driving—Enables Digital Viewing and Navigation Operation," boasts the package of one kit resting atop new navigation systems in a Tokyo store. Boxes of other converters show "before" and "after" images of a navigation screen transformed into a TV depicting a soccer game broadcast.


"We can't help but respond to our customers' needs," says Yasunari Shiino, a spokesman for Autobacs Seven Co. Ltd., which operates some 550 auto-parts stores across Japan. "This does not mean we're recommending it," he said, of a practice that could be called DWW or Driving While Watching. "Drivers need to make their own decisions."

In the U.S., televisions are popular in the back seat of minivans, but front-seat TV viewing is rare. Many states ban installation of a TV anywhere near a driver's field of vision.

Japanese companies sell car-navigation devices all over the world. But today only models sold in Japan come embedded with a tuner to enable TV watching, either automatically while parked—or while driving once unlocked with kits sold for $15 to $35 at most auto-parts stores. Japanese blogs abound with advice for do-it-yourselfers showing how it is done with minimum fuss.

"All of our 'navi' systems sold in Japan have a TV tuner function, but none sold outside Japan have it," said Pioneer Corp. 6773.TO -3.65% Pioneer Corp. Japan: Tokyo ¥211 -8 -3.65% March 14, 2014 3:00 pm Volume : 6.22M P/E Ratio N/A Market Cap ¥78.54 Billion Dividend Yield N/A Rev. per Employee ¥20,286,700 More quote details and news » spokesman Hiromitsu Kimura. "Outside Japan there's no custom of watching TV in cars."

Kaori Hirata, a 35-year-old mother of two who rises before dawn to make it to work as a prep cook, says she tunes in while driving her minivan to catch up on current events. "It's the only time of day I have a TV to myself," she says.

Ms. Hirata says when she and her husband recently decided to buy a new car, she overcame his objection to spending $800 on a navigation system with a TV and DVD player in the center console. "It was nonnegotiable," she says.

Playing DVDs of her favorite musical group while on the road "is a form of therapy for me," says Ms. Hirata, a fan of a popular Japanese boy band called Arashi.

Tatsuo Yamagoshi, a 36-year-old office worker, recently turned on the TV in his minivan's navigation system to entertain his children while parked outside a store near Tokyo.

As his wife shopped, two boys in the back seat strained to see a popular Japanese cartoon show about a bean-paste-filled superhero on the 6-inch-wide screen. "I tell myself it's for the kids, but if the news is on I can't resist watching while driving," he said. "I know that's a bad idea," he said sheepishly, adding he usually tries to limit glances to stoplights.

Hirofumi Yoshitome, 62, installed a navigation system in his car more than nine years ago, then had a friend tweak the device so he could tune in to baseball games and other programs. However, Mr. Yoshitome, a fan of the Yomiuri Giants, says these days, "I have realized that it would be better to watch at home."

What makes Japan's widespread DWW particularly surprising is that Japan has some of the most stringent traffic laws in the world—such as a zero percent blood-alcohol standard for drivers.

In 2004, Japan's laws were tightened to ban drivers from talking on cellphones, unless they are using hands-free devices. But the rules specifically exempted "stationary" equipment such as navigation systems.

Japanese law prohibits "staring" at a screen while driving, without saying anything about glancing at one.

According to the Japanese National Police Agency, the number of vehicle accidents caused by staring at a screen totaled 925 in 2011, the latest figure available, up more than 10% from 2009. That was just a fraction of the total of 691,937 reported traffic accidents in 2011.

Some experts suspect that data understates the impact of DWW.

Police in rural Tokushima prefecture have raised an alarm about an increase in accidents caused by distracted drivers with front-seat screens, including at least one death in 2011. They have cited 14 fender benders in which those behind the wheel admitted to being too absorbed by the screen to watch the road. However, police in the prefecture haven't reported catching anyone in the act.

"It's relatively easy to spot a driver using a cellphone, but it's very tough to figure out whether someone is making improper eye contact with the dashboard," said Koshiro Sawaguchi, of the Tokushima Police Department.

"It's just plain dangerous," said Yoichi Sekiyama, a 40-year-old driver without a navigation system, taking a break at an expressway rest stop. "It bothers me when I see drivers watching TV—it really shouldn't be legal."

But outside some scattered chat-room complaints, there is no sign of any widespread opposition to the practice, or move to ban it.

There are no statistics showing how many of Japan's drivers are watching more than the road. Government data does show about half of all Japanese vehicles have navigation systems. TV functionality dates back to 1997, when the first system debuted.

"The original navigation screens used the same cathode tubes as TVs, so it was pretty easy to pop in a tuner device. We engineers thought it a bit silly, but our car dealers just loved it," said Hiroyuki Watanabe, Toyota Motor Corp.'s 7203.TO -2.95% Toyota Motor Corp. Japan: Tokyo ¥5551 -169 -2.95% March 14, 2014 3:00 pm Volume : 17.15M P/E Ratio 9.56 Market Cap ¥19139.83 Billion Dividend Yield 2.70% Rev. per Employee ¥74,833,100 03/07/14 Car Makers Try to Make It Big ... 03/05/14 Australian Exporters Reap Curr... 03/04/14 Nissan sees slower growth in C... More quote details and news » senior technical executive. "It still bothers me when I hear about drivers misusing the technology. It's irresponsible."

—Miho Inada contributed to this article.

Write to Chester Dawson at