Most states have laws against watching televisions in the front seat, though many of the laws have not been updated to include DVD players and other new technologies. New York law prohibits cars from being "equipped with a television receiving set within view of the operator." But an updated California law that took effect in January bans most video functions in the front seat, including DVD players, with the exception of such technologies as navigation systems.

Automakers often install video screens for passengers in the front seat, but only features like navigation systems or stereos can typically be operated while the car is in motion, though the proliferation of electronic controls in luxury cars is also the focus of scrutiny by safety researchers.

"We know that all kinds of distractions can be a problem, but it would be hard to think of something more distracting than watching a video while you're driving," said Anne McCartt, a vice president for research at the Insurance Institute for Highway Safety, a group financed by car insurers. "It's a really worrisome trend."

She said swapping an air bag for a video screen was even more disturbing.

"It's taking out a safety device that has proven lifesaving benefits," Ms. McCartt said, "and replacing it with something that could clearly be distracting and potentially dangerous."

In recent years, car customization has becoming a booming business, and TV shows chronicling cool cars and car makeovers have proliferated, including "Overhaulin"' on TLC and "Ride with Funkmaster Flex" on Spike TV. Over the last decade, annual spending on after-market car parts and accessories has doubled to $28.9 billion a year, according to the Specialty Equipment Market Association.

"Pimp My Ride" on MTV -- with its host, Alvin Joiner, a Detroit native better known as the rapper Xzibit -- is a feel-good show in which 18- to 22-year-olds are invited to submit their dilapidated cars or trucks for a major retrofit by West Coast Customs.

In one episode, for instance, a sad-looking 1989 Ford Mustang was remade to include a photo booth built into the passenger side with a camera in the visor and a printer in the center armrest.