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It depends on whom you ask. Are high-tech digital billboards that can change their message every few seconds a lively, promising source of ad revenue? Or are they an ugly road distraction?

That debate is raging in city halls across the country as the digital-billboard industry starts to take off. In recent months, such municipalities as Atlanta; Concord, N.H.; Eden Prairie, Minn., and Des Moines, Iowa, have banned or limited the use of the signs. The Federal Highway Administration is now studying whether they threaten driver safety on interstate highways.

The industry has putup about 500 signs so far, at a cost of $250,000 to $500,000 apiece. By 2017, the number of signs could grow tenfold. The signs are not the interactive, moving pictures (called "spectaculars" in the biz) seen in places like Las Vegas or Times Square. Instead, federal rules require that only static, fixed pictures can be shown on major highways, though the pictures can change every six to eight seconds. The industry says the digital signs have been widely used to promote public safety by displaying items like seat-belt reminders and Amber Alerts. Calvin Klein just started experimenting with interactive digital billboards in Toronto that ask questions of passersby; in turn, the signs respond to answers sent in by cell phone. Is one of the questions "Are you distracted?"