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David J. Phillip, Associated Press
A motorist uses a cellphone while holding the steering wheel and a cigarette in her other hand while passing through an intersection Wednesday, Dec. 14, 2011, in Houston. The National Transportation Safety Board declared Tuesday that texting, emailing or chatting on a cellphone while driving is just too dangerous to be allowed anywhere in the United States and is urging all states to impose total bans except for emergencies.

WEST PALM BEACH, Fla. — A driver in the next lane is moving his lips. Is he on a hands-free cell phone or just talking to himself? If lawmakers follow the advice of a federal board, police officers will have to start figuring that out.

The National Transportation Safety Board said this week that drivers should be barred from using all cellphones — hand-held or hands-free. Such a law would be more restrictive than anything now on the books, and many police wonder how they could enforce it.

Capt. Donald Melanson of the West Hartford, Conn., police says it would be tough to determine if someone was on a phone or exercising their vocal cords.

An expert says a total ban would be too draconian, but a law professor says it probably would be constitutional.