Safety advocates who worry about the dangers of distracted driving have a new concern beyond cellphones and gadget-laden dashboards: digital roadside billboards.

These high-tech billboards marry the glow of Times Square with the immediacy of the Internet. Images change every six to eight seconds, so advertisers can flash timely messages — like the latest headlines, coffee deals at dawn, a cheeseburger at lunchtime or even the song playing on a radio station at that moment.

The billboard industry asserts there is no research indicating they cause crashes, and notes that the signs do not use video or animation.

But to critics, these ever-changing, bright billboards are “television on a stick” and give drivers, many of them already calling and texting, yet another reason to take their eyes off the road.

Abby Dart, executive director of Scenic Michigan, a nonprofit group trying to block construction of new digital billboards in the state, calls the signs “weapons of mass distraction” and says they can be more dangerous than phones.

“You can turn off your phone,” she said. “The billboard gets your attention whether you want to give it or not.”

Last Thursday, Michigan lawmakers held hearings on legislation, the first of its kind, that would impose a two-year moratorium on the construction of new billboards. Minnesota’s legislature is scheduled to hold hearings this month on a similar moratorium. As digital billboards begin to pop up around the country, questions about whether to regulate the emerging technology are being asked in other states as well, and by federal officials.

The Federal Highway Administration has been conducting a study, which it says will be completed this summer, that uses eye-trackers inside cars to see whether drivers who have volunteered for the study look at the digital billboards, and for how long. The agency also has organized a tour this spring to take researchers to various cities around the world to study how other nations are regulating digital billboards.

In the United States, only about 2,000 of the nation’s 450,000 billboards are digitized, but the industry expects there to be tens of thousands of them, as many as 15 percent of its overall inventory.

The signs are typically used in busy traffic areas, where advertisers are willing to pay a premium for them. A digital billboard costs $250,000 to $300,000, roughly half what it did five years ago, but much more than the $5,000 to $50,000 for a traditional billboard.

Space on the digital signs fetches a premium in part because up to six advertisers can share a single location. Traditional billboards fetch a wide range of monthly rents (from $1,000 to $5,000 depending on location and audience) and the digital versions cost the same or a bit more, but the industry benefits by selling that space at that price to more than one advertiser.

Rather than settling the matter, existing research about digital billboards leaves room for debate on the danger.

One 2007 study, from the Virginia Tech Transportation Institute, which used in-car cameras to study motorists, found that digital billboards did not change driver behavior more than ordinary billboards.

But critics note that the study was financed by the billboard industry and that it was found to be biased by reviewers who rejected it for publication in 2008 by the Transportation Research Board, a Congressionally chartered agency.

Even the researcher who led the Virginia Tech institute project, Suzanne Lee, while defending her science as sound, said that the potential for drivers to be distracted by the new billboards — and digital signs that use video and animation — should be investigated further.

“If we don’t study this, and get on top of it right now while the capabilities are expanding, every roadway will be filled with flashing lights and video,” said Ms. Lee.

For decades, the Federal Highway Administration has provided regulations to states governing free-standing billboards that prohibit them from having “flashing, intermittent or moving light or lights.”

But in 2007, the agency ruled that the free-standing digital billboards did not violate the rule and recommended, among other guidelines, that ads on those billboards stay in place at least four seconds and that they not be “unreasonably bright.”

Last week, the Georgetown Institute for Public Representation, a public interest law group, filed a petition with the highway administration asking it to reverse the earlier decision, which would have the effect of banning new digital billboards that include flashing, intermittent or moving lights, and requiring the dismantling of existing ones.

The billboard industry argues that the new signs are part of a larger technological and economic shift to a paperless society (no more crews hoisting and removing ads from billboards) and that they give advertisers more flexibility.

Marketing materials published last year by Clear Channel, one of the nation’s biggest billboard companies, say the digital billboards are, among other things, ideal for posting game scores by advertisers like radio stations and sports bars. News organizations can also use them — “as the Web site headline changes, so does the digital billboard,” the materials say.

”It’s a very flexible, very responsible medium and very impactful,” said Ron Cooper, chief executive of Clear Channel Outdoor, which has 450 digital billboards and plans to add 150 more this year. Big corporations that have used them include ABC, AT&T, Coca-Cola, McDonald’s, General Mills, Ford and Verizon. “Consumers report seeing it, remembering the brand, remembering the advertisers.”

He and others in the industry say they have been careful to make the signs memorable but not distracting. They say the “television on a stick” label is an exaggeration.

“It’s a slide projector — it shows one image after the next,” said Bill Ripp, a vice president who oversees digital billboards for Lamar Advertising, another large billboard company. “We were as concerned as anybody. We wouldn’t want to cause danger.”

The industry has found an ally in some crime-fighting groups and agencies, including the Federal Bureau of Investigation and the National Center for Missing and Exploited Children, which use the new signs to broadcast images of fugitives or of abducted children.

“We’ve had moms grab their sons by the ear and drag them right down to the sheriff’s office because they were embarrassed to see the son on the billboard,” said Bart Dexter, coordinator of the Michigan Crime Stoppers organization, who opposes the Michigan moratorium.

Ms. Dart, from Scenic Michigan, said the potential driver distraction outweighs any help the signs may provide in catching fugitives.

Rebekah Warren, a Democratic state representative from Ann Arbor, who proposed the moratorium, said the bill reflected broader concerns that legislators around the country had about distracted driving. In December, the Michigan House of Representatives passed legislation banning motorists from texting, something its Senate now is considering.

“We are moving so quickly into this digital age,” said Ms. Warren. “We are being cautious in state legislatures around the country on how we keep drivers focused on the road.”