Federal employees will not be allowed to text while driving, according to an executive order signed Wednesday night by President Barack Obama. The order covers federal employees when they are using government-provided cars or cell phones and when they are using their own phones and cars to conduct government business. Separately, the federal government plans to ban text messaging by bus drivers and truckers who travel across state lines, and may also preclude them from using cell phones while driving, except in emergencies. Ray H. LaHood, the Transportation secretary, announced those and several other measures on Thursday, aimed at curbing what he called a deadly epidemic of distracted driving. He made his announcement at a conference in Washington that included 300 academics, law enforcement officials, legislators, telecommunications and automobile industry representatives, as well as families of people killed by motorists who were talking on cell phones or text messaging. 'This meeting is probably the most important meeting in the history of the Department of Transportation,' LaHood said at the end of the two-day conference. He added that the order to restrict text messaging by federal employees behind the wheel 'sends a very clear signal to the American public that distracted driving is dangerous and unacceptable.' A spokeswoman for the Transportation Department said the order took effect immediately and involved 4.5 million federal employees, including military personnel. According to the National Safety Council, a nonprofit safety advocacy group, several hundred companies have banned employees from using their cell phones while driving. That group says such bans improve safety, help limit the liability of employers when accidents do occur, and free employees from feeling pressure to respond immediately while they are behind the wheel. The rules affecting interstate truckers and bus drivers will take longer to put in place and may be more nuanced. LaHood said the rule would 'ban text messaging altogether' by such drivers. But Rose A. McMurray, acting administrator for the Federal Motor Carrier Safety Administration, which regulates the trucking industry, said there would first need to be a definition of 'text messaging.' The question facing the trucking industry in particular is what will become of the computers that thousands of long-haul truckers use in their cabs to communicate with dispatchers and do other work. Research from the Virginia Tech Transportation Institute shows that these devices can markedly increase the risk of causing a crash or near crash if used when driving. Its research also shows that truckers often bypass warnings to not use the devices while driving. McMurray said she expected that it would take several months to complete a rule governing buses and trucks, during which time the agency would study the 'array of devices' used by these drivers. She said that she expected to ban truckers from texting with their phones and also to ban behavior 'that would require fingers to manipulate a keyboard, or to take the eyes off the road' to use a keyboard and, possibly, other technologies used for typing. The trucking industry has said it is concerned that texting bans in general could have unintended consequences of interfering with devices that truckers have come to rely on. McMurray said it was also not yet clear how the rule would restrict the use of cell phones by these drivers. She said it could include a ban altogether on the use of such phones by interstate truckers and bus drivers, except in cases of emergency, but she said that rule would also take time to complete. She said the need to take such steps was in part 'because of the size of the vehicles.' The distracted driving conference provided a forum for a range of different interests hoping to raise awareness of distracted driving and influence how the issue is addressed. The speakers included Sens. Charles E. Schumer, D-N.Y., and Robert Menendez, D-N.J., who have introduced legislation to force states to ban texting while driving or lose federal highway funds. Some people left the gathering concerned that the conference emphasized texting bans over risks posed by drivers talking on cell phones. That issue was discussed, but less so than texting. Critics said the texting issue seemed like an easier issue to address politically. Banning texting 'makes people feel good and makes it look like you're doing something, but you're not tackling the more difficult problem,' said David Strayer, a professor at the University of Utah who studies distracted driving. 'It misses the larger point.' 