At one time, the National Association of Broadcasters (NAB) code recommended a limit of 18 minutes of commercials per hour on radio. But the NAB discarded the code when in 1984 the U.S. Justice Department alleged that the standards, although voluntary, violated antitrust laws by promoting limits that discouraged competition.

     Historically, astute station management has carefully limited commercial load. When the legendary Bill Drake reinvented top 40 radio at KHJ in Los Angeles in the 1960s, he maintained an "iron-clad" hourly limit on commercials. Drake ordered that commercials should not exceed 13 minutes, 40 seconds per hour, nearly one-third less than the U.S. average at the time. When FM finally became successful in the late 1960s and early 1970s, listeners perceived it as the "less-commercials band," and operators wanting to maintain their stations' success instituted firm policies limiting the number of spot announcements per hour.

     Since the top 40 hit-music format emerged in the 1950s, radio stations have grouped commercials in clusters called "sp t sets" (or "stop sets"). A common approach has been to promote longer "sweeps" of uninterrupted music, a strategy that requires fewer but longer commercial breaks. However, an Arbitron/Edison Media Research study found strong support for more frequent, and shorter, spot sets. Fifty-two percent of those surveyed preferred more frequent stops with shorter blocks of commercials, while 39 percent preferred longer programming blocks and longer blocks of commercials. The findings led the report's authors to recommend that radio stations consider changes in their spot-clustering paradigms, but only after conducting research of their own audience's listening habits.

     The number of commercial minutes each hour is entirely up to the management of each individual station. Increasingly, writers on the topic are concerned that a trend toward increasing the number of commercials per hour is having a negative effect on radio listenership. The Radio Advertising Bureau reported that radio-advertising revenue exceeded $17 billion in 1999, up 15 percent from the previous year. However, radio listenership had declined 12 percent over the past decade, according to the consulting firm Duncan's American Radio, with only 15.4 percent of the national population age 12 and over listening in any quarter hour, 6 A.M. to midnight, down from 17.5 percent in 1989. One of the reasons for the decline, according to Duncan's, is the trend toward higher spot loads. Some sources report stations airing up to 22 commercial minutes per hour.

     A 2000 study by Empower MediaMarketing of Cincinnati found that the number of paid advertisements on radio stations grew by about 6 percent in the previous year. The greatest increase was in the San Francisco-Oakland-San Jose, California, market, where the number of 10-, 30-, and 60-second spots increased by 20 percent (see Kranhold, 2000). A 2001 Arbitron study found that advertisers perceived radio as the most "cluttered" mass communications medium. Although clutter (or the absence of clutter) was not considered a key criterion by most advertisers, the report recommended reducing spot loads.

     Another Arbitron report suggests that higher commercial loads are turning off audiences. In the report titled "Will Your Audience Be Right Back After These Messages?" Arbitron and Edison found that 42 percent of radio listeners had noticed that stations are airing more commercials, although, interestingly, listeners are not as likely to believe that their own favorite station is playing more spots. Young listeners seem to be the most annoyed by the trend. The report found 31 percent of listeners ages 12-24 said they were listening to radio less, while 17 percent of listeners in the 25-54 demographic, and 11 percent of those 55 and older, said they were listening to less radio. The report suggests that the greater number of commercials is a major reason for the decline in time-spent-listening. Advertising agencies, on the other hand, suggest the results show the need for more entertaining commercials.

     A Washington, D.C., station, WWVZ, seemingly took to heart Arbitron's advice to reduce commercial spot loads. The station implemented a format with only two three-minute commercial breaks per hour. An advertising executive with Hill Holliday in Boston, Karen Agresti, hailed the station's decision. "Clutter is one of the biggest problems in radio. For a station to take a lower load is great, and I hope more will do it," she said. WBLI-FM (Long Island, New York), a contemporary hits station, cut its commercial load from 16-17 minutes per hour to 10-11 minutes. The station gained 3.5 ratings points among its core audience, women I 8-34.

     In an attempt to make room for more commercials, some radio (and television) stations have begun using a device called "Cash," which uses audio delay and "intelligent micro­ editing" to create up to six minutes of additional commercial time per hour. The use of Cash drew criticism from the president of the American Association for Agencies, O. Burtch Drake. Drake said radio will not benefit in the long run from creating more clutter. "You can shoehorn more commercials in, but it hurts both the station and the advertiser," Drake said. "That's why we are taking a very strong stand against this kind of technology."

     As a way to cut through the clutter, and as an alternative to hiring high-profile celebrity endorsers, some advertising agencies are advising clients to find popular local radio personalities to endorse their products.