A driver in the next lane is moving his lips. Is he on a hands-free cellphone? Talking to someone in the car? To himself? Singing along to the radio?
If lawmakers follow the advice of a federal board, police officers will have to start figuring that out - somehow.
The National Transportation Safety Board said this week that drivers should not only be barred from using hand-held cellphones, as they are in several states, but also from using hands-free devices. No more "Sorry, I'm stuck in traffic" calls, or virtually any other cellphone chatter behind the wheel.
Though no state has yet implemented such restrictive rules, the NTSB's recommendations carry weight that could place such language into future laws, or motivate the federal government to cut funding to states that don't follow suit.