Boston — If, in the near future, your car radio suddenly cuts off a cassette tape in mid-Mozart, switches to an FM station, and cranks up the volume, don't search the skies for alien spacecraft - just listen for a brief traffic update.
The West German radio manufacturer, Blaupunkt, has just begun marketing such a sophisticated radio in New York City. Four local FM radio stations already broadcasting traffic information now are equipped with the technology to trigger the automatic functions of the new radio. A Blaupunkt spokesman says the company expects to have the Automatic Radio Information (ARI) system in ''at least 20 major city areas in the United States within the next two years.'' Boston, Chicago, Philadelphia, Houston, San Francisco, and the Los Angeles-San Diego corridor are among the cities targeted.
The European Broadcast Union selected Blaupunkt to develop the radio 10 years ago to help untangle massive traffic snarls on European highways during the peak weeks of summer vacation. Helicopter traffic observers could see that most cars were traveling on the same roads while alternate routes were wide open. The problem was how to get the message to drivers paying little attention to background music or the yammering of radio announcers.
The solution was a hybrid computer chip, built into each radio unit, that receives a subaudible tone broadcast over existing local FM networks. Signs along major roads tell West German drivers what station to tune to in each area. As long as the radio unit is tuned to the correct station, even at low volume, the traffic or emergency messages will get through.
Christian Stettler, an official of the International Consultative Committee for Radio Communications in Geneva, says the traffic information service, used throughout West Germany, Austria, and Switzerland, has been very successful. In the last five years, almost 90 percent of the FM radios in West German cars, he says, have come to feature the ARI technology. Bosch, Blaupunkt's parent firm, as well as Volkswagen, BMW, and Mercedes Benz officials confirm this.
Mr. Stettler says the receivers on the European market vary in price from $ 200 to $450. Japanese radio manufacturers including Sony and Pioneer also make the special car radios for European cars, using the hybrid computer chip under license from the German firm. So far, only Blaupunkt models (ranging from $160 to $450 in the US) are available in the New York area. However, a Blaupunkt spokesman says both American and Japanese manufacturers will be licensed to use the ARI technology as the American market opens up.
The Federal Communications Commission (FCC) in Washington gave the ARI system the green light in the US, says Bob Greenberg of the FCC's Broadcast Bureau, because ''it seems to work overseas, and it looked to be in the public interest - that's why we granted it (authorization).''
Richard Neer of WNEW-FM, one of the four FM stations involved with Blaupunkt's ARI system in New York City, says ''the service started one month ago, but it is too early to tell what effect it is having - there can't be more than a dozen radios out there.''
Each day a WNEW-FM reporter compiles hourly reports using information provided by Shadow Traffic, a local information service in New York. The station then transmits the subaudible tone and broadcasts its accompanying traffic update three times each hour during rush hour and once each hour during normal hours, advising motorists of alternate routes or severe weather conditions.
A Blaupunkt spokesman says each radio station is allowed a 10-second tag advertisement at the end of each broadcast, but the FCC requires that the station not abuse the ARI system by broadcasting anything other than public-service information.
But is it the wave of the future or just another expensive gimmick?
''At this point it is almost gimmicky, but in the near future, it will be much, much more useful to consumers,'' says Paul Benedict of Radio a La Carte, a car stereo store, in Piscataway, N.J. ''Believe me, traffic is a nightmare at rush hour in New York City.''