For nearly 100 years, drivers have been listening to AM radio, an American institution crackling with news, traffic, weather, sports and an eclectic variety of other programs.But such changes require money and effort, and it’s not clear whether carmakers are willing to spend more in the service of AM radio fans.“It’s a killer for us because most of our listening audience is in the morning drive and afternoon drive, when people are going to work and coming from work — and if we’re not there in their car, we’re nonexistent,” said Ron January, operations manager at WATV-AM, an adult contemporary station in Birmingham, Ala. About 47 million Americans listen to AM radio, representing about 20 percent of the radio-listening public, according to the Nielsen Company, the media tracking firm.Is FM next?” In a letter to 20 car manufacturers published on Dec. 1, Senator Edward J. Markey, Democrat of Massachusetts, requested that they keep AM radio in electric vehicles, describing it as an issue of public safety.“As a result, any phaseout of broadcast AM radio could pose a significant communication problem during emergencies.” Many AM broadcasters say their stations’ news reports are the quickest way for drivers to find out about tornadoes, flash floods and other severe weather."