When drivers don't respond to a 4- to 8-second chime telling them to buckle up, it helps to keep reminding them. But, as a new Institute study shows, those reminders don't have to take the form of a continuous, unrelenting chime to be effective.
Researchers looked at the reactions of 80 part-time belt users to various safety belt reminder systems and found that systems that chime for a total of 90 seconds, either continuously or intermittently, work better than a system that has only the required 4- to 8-second signal. Intermittent chimes were less annoying to people but were deemed just as effective as continuous ones.
Despite great strides in belt use in recent decades, 15 percent of drivers still don't buckle up, and unbelted vehicle occupants are overrepresented in fatal crashes. If all passenger vehicle occupants 5 years and older involved in fatal crashes had been restrained, nearly 3,700 deaths could have been avoided during 2009, the National Highway Traffic Safety Administration has estimated (see "Low-hanging fruit," Aug. 18, 2011).
Effectiveness ratings for basic vs. enhanced belt reminders
Responses for enhanced reminders recorded after 90 seconds of active chiming
Most people who don't buckle up are part-time belt users, meaning they sometimes use belts, but not on every trip. In surveys, a common reason cited for not buckling up is forgetfulness.
"A short chime and flashing icon can get lost amid all the other signals at start-up," says Anne McCartt, the Institute's senior vice president for research. "If people are simply forgetting to buckle up, a longer, more noticeable reminder should help them remember."
In the United States, vehicles are required to have an auditory belt reminder lasting just 4 to 8 seconds and a visual warning. The National Highway Traffic Safety Administration is prohibited by law from requiring a longer buzzer or chime. That ban dates back to 1974, when Congress also prohibited the agency from requiring safety belt ignition interlocks, which prevent an unbelted driver from starting a car. Congress acted after manufacturers began installing interlocks to comply with occupant protection standards, prompting protests from consumers.
The agency encourages manufacturers to install belt reminders that exceed the requirements, and the vast majority do so for drivers. Studies have found that such enhanced belt reminders lead to higher rates of belt use, and an Institute analysis found that driver fatality risk was 2 percent lower for vehicles with the enhanced reminders than for vehicles without them (see "Belt reminders reduce deaths among drivers," July 11, 2009). However, anything with an audible warning longer than 8 seconds could be considered enhanced, and the systems vary widely.
Based on information provided by manufacturers, Institute researchers estimate that at most about a quarter of 2011 models sold in the United States have 90 seconds of active chiming in their belt reminders. Such systems are more common in Europe because the European New Car Assessment Programme (Euro NCAP) awards points in its vehicle rating system for belt reminders with at least 90 seconds of visual and auditory warnings. To qualify, the warnings can be constant or have gaps of up to 25 seconds. In other words, a reminder that goes off every 30 seconds for 5 seconds for a total of 9 minutes would meet the requirements just as well as a system that beeps and flashes continuously for a minute and a half.
To study how U.S. drivers respond to different types of systems, researchers had people experience them in a driving simulator. The Institute worked with Dynamic Research Inc., which recruited people who reported being part-time belt users. Participants had to be between the ages of 18 and 65 and have at least a year of driving experience.
As participants drove in the simulator for 7½ minutes, they experienced either a basic belt reminder, consisting of a 6-second chime and a continuously illuminated signal, or 1 of 3 enhanced systems with chimes and flashing signals lasting the entire trip. The enhanced systems included a continuous chime and flashing signal; a 50 percent system, in which a chime and signal were active for 15 seconds and then paused for 15 seconds; and a 20 percent system, in which a chime and signal started every 30 seconds and lasted 6 seconds.
The participants were asked every 45 seconds how likely it was that they would have buckled up. Those driving with the enhanced reminders were more likely to say they would have than those with the basic reminder.
On a scale of 1 to 10, with 1 meaning they definitely would not have buckled up and 10 meaning they definitively would have, participants gave the basic system an average rating of close to 5 after 90 seconds. In contrast, the 3 enhanced systems were all rated about 9. This comparison used the ratings taken after the warning had sounded for a total of 90 seconds — at the 90-second point for the continuous enhanced reminder, 3 minutes for the 50 percent system, and 7½ minutes for the 20 percent one. Each system would have met the Euro NCAP standard at those points.
Not surprisingly, the enhanced systems were judged more annoying than the basic system. Over the course of the entire drive, the basic one had an average rating of about 2 for annoyance, with 1 being not annoying and 10 being extremely annoying. The enhanced system that chimed constantly rated about 8. However, the intermittent systems were slightly less annoying, each rating about 7.
"This study shows that manufacturers have a variety of options when it comes to encouraging safety belt use," McCartt says. "Intermittent systems may do just as good a job of getting people to buckle up without being as big an irritation to consumers."