NEW YORK - Sending an SMS, emailing or chatting on a cellphone while driving are simply too dangerous to be allowed, US federal safety investigators have declared and urged all states to impose total bans except for an emergency.Inspired by recent deadly crashes - including one in which a teenager sent or received 11 text messages in 11 minutes before an accident - the recommendation would apply even to hands-free devices.The unanimous recommendation by the five-member National Transportation Safety Board made an exception for devices deemed to aid road safety, such as GPS navigation systems.'GAME CHANGER'A group representing state highway safety offices called the recommendation "a game-changer". Jonathan Adkins, a spokesman for the Governors' Highway Safety Association, said: "States aren't ready to support a total ban yet, but this may start the discussion."Driving rules and limitations in the US are, generally, the job of the state legislatures, even on federally built roads such as the interstate highway system.NTSB chairwoman Deborah Hersman acknowledged the recommendation would be unpopular with many people and said complying would involve changing what has become ingrained behaviour for many Americans.AGGRESSIVE ENFORCEMENTWhile the NTSB lacks the power to impose restrictions, its recommendations carry significant weight with federal regulators and congressional and state lawmakers. Another recommendation urges states to enforce aggressively current bans on text messaging and the use of cellphones and other portable electronic devices while driving."We're not here to win a popularity contest," Hersman said. "No email, no text, no update, no call is worth a human life."Only some states have banned SMS-ing while driving; nine states and the District of Columbia have banned handheld cellphone use. Thirty states ban all cellphone use for learner-drivers. But, as in South Africa, enforcement in the US is generally not a high priority, and no states ban the use of hands-free devices.