They are hard to ignore — billboards made from thousands of glowing LEDs that change ads several times a minute. While the technology is a boon to advertisers, local governments are trying to figure out how best to regulate digital displays so they do not distract drivers or bother nearby residents.

Nationwide, about 1,500 digital billboards, also known as electronic variable message signs, are operating along highways, says Outdoor Advertising Association of America spokesperson Jeff Golimowski, up from an estimated 700 two years ago. Because new billboards are banned in many places, some static signs have been replaced with digital displays that Golimowski says can cost more than $200,000.

As the number of LED signs increases, so has the number of jurisdictions questioning their place within local sign laws. "Any type of roadway distraction is a concern of ours," says Richland County, S.C., Administrator Milton Pope.

Elected officials there have considered repealing a 2001 moratorium on all new billboards. Since the moratorium was enacted, though, digital signs emerged as a popular new advertising medium. When Columbia, the largest city in Richland County, began allowing the signs on a limited basis, a large manufacturer of the sign asked the county to consider following suit.

In addition to the debate over billboards' place in the community, commissioners now also must consider LED displays that are much more visually jarring, leading to concerns about their safety. In 2007, two studies, conducted by the Virginia Tech Transportation Institute and Tantala Associates, concluded the signs did not pose a danger. Both were funded by the industry, though, and have been disputed by critics and in a peer review commissioned by the Maryland State Highway Administration. Stakeholders in the debate are awaiting a more extensive Federal Highway Administration study on the displays, which is due out later this year. In the meantime, municipalities from Reno, Nev., to Bonita Springs, Fla., are reviewing their sign codes to determine how bright the signs should be, where they may be placed, and whether LED billboards should be allowed at all.