Increasing seat belt use in the United States by promoting and requiring more effective seat belt reminder systems

Abstract

Objective

Federal Motor Vehicle Safety Standard (FMVSS) 208 requires every passenger vehicle to provide an auditory signal lasting 4 to 8 seconds and a visual display lasting 60 seconds when the driver is unbelted at ignition. This requirement does not increase seat belt use. This paper summarizes the latest research on using vehicle technology to increase seat belt use and existing safety standards worldwide to support the strengthening of FMVSS 208.

Method

Studies of seat belt reminders and interlocks published in peer-reviewed journals, conference proceedings, or as technical reports were identified in online databases and reviewed along with current requirements worldwide. Results from past research were used to estimate the front- and rear-seat daytime belt use rate and the annual number of lives that could be saved by a persistent audible reminder at each seating position.

Results

Most motor vehicle occupants routinely buckle up. Those that do not typically forget, are going a short distance, or find belts uncomfortable. Seat belt reminders can remind or motivate occupants to buckle up. Enhanced reminders that exceed FMVSS 208 increase belt use by 6 percentage points. Reminders also can increase rear belt use, and although required throughout the world, are not required by FMVSS 208. More persistent reminders, like those required around the world, with a continuous, long-lasting audible signal increase belt use by 30% among drivers who do not routinely buckle up. If every vehicle in the U.S. had such a reminder at each seating position, then it was estimated that the daytime belt use rate in the U.S. would increase about 3 percentage points from 90.3% to 93.2% in the front row and by about 6 percentage points from 80% to 85.9% in the rear row. It was estimated that the increase in belt use from a continuous, long-lasting audible reminder could potentially save about 1,600 lives each year.

Seat belt interlocks can increase belt use, but acceptance is a stumbling block. Public outcry ensued after interlocks were required in 1973, and public sentiment remains negative. Opinions toward front and rear reminders are more favorable. Furthermore, past research suggests interlocks may be no more effective for increasing seat belt use than persistent audible reminders. The effect of interlocks on rear belt use have not been explored.

Conclusion

Persistent seat belt reminder systems that last at least 90 seconds can potentially save hundreds of U.S. motorists each year. Robust empirical evidence, successful exemplars from organizations throughout the world, and a clear public health benefit exists for strengthening FMVSS 208 to require more persistent audible reminders at every seating position.

Keywords:

• Seat belt reminder
• seat belt interlock
• seat belt use
• occupant protection
• restraint use

Introduction

Seat belts are the most important safety feature in motor vehicles. When worn properly, seat belts reduce the risk of injury in a crash by spreading crash forces across the strong, bony parts of the body. They keep occupants from hitting structures in the vehicle during a crash and keep them from being ejected out of it. Seat belts reduce the fatality risk of front-row occupants by 45% in passenger cars and by 60% in light trucks (Kahane 2000). Fatality risk for belted rear occupants is reduced by 58% in passenger cars and 75% in light trucks (Kahane 2017). The National Highway Traffic Safety Administration (NHTSA) estimates that seat belts save around 15,000 lives each year and have saved nearly 330,000 lives between 1960 and 2012 (National Center for Statistics and Analysis 2019).

Seat belt use in the United States (U.S.) is higher than ever, but lack of belt use continues to be a major factor in fatal motor vehicle crashes. In 2020, 90.3% of front-row occupants and 80% of rear row occupants observed at controlled intersections during the daytime were using a seat belt (Enriquez 2021). However, only 49% of passenger vehicle occupants in 2020 were restrained in fatal crashes where belt use was known (Stewart 2022). If every occupant over 4 years old was belted, then an estimated additional 2,549 lives could be saved each year (National Center for Statistics and Analysis 2019).

Demographics (e.g., Boyle and Lampkin 2008), personal beliefs (e.g., Jermakian and Weast 2018), and state laws (e.g., Enriquez 2021) all influence seat belt use. Forgetting to buckle, situational factors (e.g., traveling a short distance, at low speeds, or in a hired ride), and comfort also are common reasons why both front and rear occupants report not using a seat belt (Dahlstedt 1999; Jermakian and Weast 2018; Kidd et al. 2014b; Richard et al. 2019; TRB 2003). Rear occupants also commonly state convenience as a reason for not using a seat belt (Eby et al. 2005). In a national survey, adults who regularly transported children in rear seats said that their rear child passenger was unbuckled when the trip began or unbuckled during the trip (Kidd and McCartt 2014a). In other situations that are not routine, like riding in the back of a hired ride, people report not knowing why they did not use a seat belt (Jermakian and Weast 2018).

Forgetting to use a belt, not knowing, and other reasons why people do not regularly use a seat belt could be addressed using vehicle technology like seat belt reminders and interlocks. Seat belt reminders use a combination of visual and audible signals to prompt forgetful occupants to buckle up, notify unaware parents of an unbuckled rear child occupant, or nag unbuckled occupants sufficiently to encourage belt use. Seat belt interlocks shape behavior or compel belt use by preventing the vehicle or certain features from being used when an occupant is unbelted.

Existing safety standards in the U.S. require notifications when the driver is unbelted, but these requirements are antiquated. Federal Motor Vehicle Safety Standard (FMVSS) 208 requires a continuous or intermittent auditory signal lasting 4 to 8 seconds and a continuous or flashing visual display lasting 60 seconds be activated when a driver is not using a seat belt at ignition. Reminders that meet but do not exceed FMVSS 208 are no more effective for increasing seat belt use than reminders that only meet the safety standard (Robertson and Haddon 1974). FMVSS 208 also does not address belt use at other seating positions.

NHTSA was prohibited from requiring longer-lasting auditory signals or providing incentives for using interlocks to increase seat belt use until recently. Starting with vehicles manufactured in August 1973, manufacturers had the option to equip vehicles without passive restraint systems with an ignition interlock that did not allow the car to start if a front passenger belt was unbuckled. Public outcry ensued, and Congress passed a law prohibiting NHTSA from requiring or allowing interlocks to be required for meeting a safety standard and limiting the duration of audible seat belt reminders (Motor Vehicle and School Bus Safety Amendments of 1974).

The Moving Ahead for Progress in the 21st Century Act (MAP-21 2012) relaxed these restrictions nearly 40 years later. MAP-21 struck language that limited the duration of an auditory reminder and revised existing regulation, so that NHTSA can allow the use of an interlock system to meet a safety standard. Despite these changes, NHTSA has not proposed rulemaking and FMVSS 208 has not changed. The purpose of this study was to review the latest research on using vehicle technology to increase seat belt use and the corresponding safety standards and requirements for the technology around the world to lay out an empirically based path for strengthening FMVSS 208.

Methods

Studies of seat belt reminders and interlocks published in peer-reviewed journals, in conference proceedings, or as technical reports were identified through online databases (e.g., Google Scholar, PubMed, ScienceDirect) using keyword variants of seat belt, safety belt, interlock, reminder, enhanced reminder, use, acceptance, buckling routine, or combinations of these keywords. Backward referencing was used to identify additional studies. Current regulations or requirements in the U.S. and other countries were obtained from government document repositories and organization websites. In total, 37 academic publications or technical reports and 13 regulatory or testing protocol documents were included in this review.

Results from the literature review were used to estimate the front- and rear-seat daytime belt use rate and the annual number of lives that could potentially be saved by a seat belt reminder system with a persistent audible reminder for each seating position. The potential effect of a persistent audible seat belt reminder on belt use in the U.S. was estimated using the following steps. First, national estimates of daytime front and rear seat belt use were subtracted from 100 to estimate the percentage of unrestrained front- and rear-row occupants. The percentage of unrestrained front- and rear-row occupants was then multiplied by the anticipated increase in belt use from a persistent audible seat belt reminder. The product was added to the original national estimate to estimate the U.S. belt use rate if every vehicle had a persistent audible seat belt reminder for front- and rear-row seating positions.

The number of lives that could potentially be saved by a persistent audible seat belt reminder was computed using the following steps. First, the number of unbelted front and rear passenger car, light truck, and van occupants who died in 2020 were queried from the Fatality Analysis Reporting System. These counts were then multiplied by the fatality risk reduction associated with restraint use in the corresponding seating position and vehicle type (Kahane 2000; 2017). The corresponding products were multiplied by the anticipated increase in belt use associated with a persistent audible reminder to estimate the number of lives the reminder could potentially save for each combination of occupant row and vehicle type. The sum of these values was the estimated total number of lives that a persistent audible seat belt reminder could potentially save each year.

Results

Seat belt reminder system effectiveness

Seat belt reminder systems with an auditory signal lasting 8 seconds or longer that exceed FMVSS 208 requirements are called enhanced seat belt reminders. Enhanced reminders are effective for increasing seat belt use compared with reminders that only meet FMVSS 208 (Freedman et al. 2007). Past research showed that enhanced reminders in Ford vehicles increased observed driver belt use 5-pecentage points (Williams et al. 2002) and increased it 6-percentage points in Honda vehicles (Ferguson et al. 2007). Though modest, even small increases in belt use reduce fatality risk (Farmer and Wells 2010).

Enhanced reminders vary across vehicles and are not equally effective at increasing seat belt use. Reminders with audible signals that continue longer and are more frequent are more effective for increasing belt use than briefer, less frequent signals (Kidd and Singer 2019a; Lerner et al. 2007). Systems with multiple warning periods increase seat belt use more than systems with a single warning period.

Several studies have found that systems with audible reminder signals that last at least 90 seconds and meet other European New Car Assessment Program (Euro NCAP) requirements increase belt use. An observational study in Sweden found that reminders meeting Euro NCAP requirements increased belt use 6-percentage points more than reminders that did not. Systems that met Euro NCAP requirements increased belt use 17-percentage points more than vehicles without a seat belt reminder system (Krafft et al. 2006). Lie (2012) analyzed fatal crashes in Sweden occurring between January 2004 and June 2010 where restraint use was known and suicide was not a factor. Lie found that 93% of occupants in vehicles with reminders lasting at least 90 seconds were restrained compared with 74% of occupants in vehicles without such reminders.

An observational study that recorded driver belt use in 7 European countries found that driver belt use was 97.5% in vehicles with a reminder meeting Euro NCAP requirements and 85.8% in vehicles without any reminder (Lie et al. 2008). Based on these findings, Lie et al. estimated that reminders meeting Euro NCAP requirements increased belt use among drivers not using a belt by 80%. Similarly, a recent U.S. study examined if observed driver and right-front passenger belt use in vehicles with different types of seat belt reminders was greater than, similar to, or less than predicted belt use after controlling for occupant characteristics, vehicle type, state belt use law, and other covariates (Polson et al. 2021). Observed driver and right-front passenger belt use was greater than predicted in 85% of vehicles with a reminder meeting Euro NCAP requirements that were observed but only 15% of vehicles with a reminder that did not meet these requirements.

A field operational test in Australia examined the belt use of 23 drivers who drove a vehicle with a multi-stage seat belt reminder with an auditory warning that became more repetitive as the vehicle’s speed increased (Young et al. 2008). Participants were unrestrained on 32% of trips taken when the reminder was inactive during the first 1,500 km of driving and unrestrained on only 17% of trips taken when it was active during the remaining 15,000 km of driving. Participants were rarely unrestrained when traveling 40 km/h or faster on trips where the reminder was active.

Kidd and Singer (2019b) had people who were previously cited for not using a belt and reported not regularly using one drive a vehicle with an intermittent seat belt reminder for one week followed by a vehicle with a persistent reminder lasting 100 seconds, an incessant reminder that never ended, or a speed-limiting interlock system that restricted speed to 24 km/h (15 mph) for another week. Relative to weekly changes in belt use when driving a vehicle with an intermittent reminder each week, the persistent reminder increased belt use 30% and the incessant reminder increased it 34%.

Reminders also can increase rear-occupant belt use. Reminders from other occupants or presented using placards in the vehicle have been shown to increase rear-passenger seat belt use (Jermakian and Weast 2018; Nemire 2019). In a national survey about rear belt use, over 60% of people who reported not always using a seat belt in the back seat said they would be more likely to buckle if there was an audible reminder (Jermakian and Weast 2018). Axelsson and Kullgren (2019) examined crash data in the Swedish Traffic Accident Data Acquisition system and compared belt use in crash-involved vehicles that had reminders for front occupants or every occupant to those without a reminder. Belt use among rear occupants 8-13 years old, 14-18 years old, and over 30 years old was 7%, 22%, and 8% higher, respectively, in vehicles with any type of reminder compared with vehicles without a reminder. Separate estimates for belt use in vehicles with reminders for every occupant or only front occupants was not reported.

Seat belt reminder system acceptance

Most people find reminders acceptable (Eby et al. 2005; TRB 2003; Kidd et al. 2014b) and want the vehicle to encourage an unbuckled passenger to buckle up, particularly if the occupant is a child (Eby et al. 2005; Kidd and McCartt 2014a). Unfortunately, more effective, longer-lasting audible reminders tend to annoy people and be perceived as less acceptable (Freedman et al. 2007; Kidd 2012; Kidd and Singer 2019a). Occupants may misuse the seat belt, buckle behind their back, or find another way to circumvent reminders that annoy them (Geller et al. 1980).

Nevertheless, people view more insistent seat belt reminders positively. Interviews with owners of Ford and Honda vehicles suggest that most liked the enhanced reminder system in their vehicle and viewed it favorably (Ferguson et al. 2007; Williams and Wells 2003). Drivers in Young et al. (2008) field operational test overwhelmingly said the seat belt reminder they experienced that became more repetitive with increased speed was both useful and socially acceptable because it did not take control away from them.

Seat belt interlock system effectiveness

Seat belt interlocks are effective for increasing seat belt use. Driver belt use in vehicles with an ignition interlock was twice as high (59%) as it was in vehicles that only had a brief reminder (28%) (O’Neill 2001; Robertson and Haddon 1974). More recent research found that interlock systems that delayed shifting into gear (gear shift interlock) or that made the accelerator harder to press increased seat belt use among fleet and service vehicle drivers (Van Houten et al. 2010, 2011). Bao et al. (2020) examined the effects of a speed-limiting interlock and gear shift interlock on the seat belt use of 48 people who did not routinely use a seat belt. The interlock systems were equally effective at increasing driver belt use, and together, reduced the amount of time the occupant was unbuckled while driving by 14.4%. Bao et al.’s findings are consistent with another study that found that people perceived speed-limiting interlocks or gearshift interlocks to be more effective for increasing seat belt use than various types of seat belt reminder systems following a brief experience with each system (Kidd and Singer 2019a).

A series of studies that examined the same interlock systems investigated by Bao et al. (2020) arrived at a slightly different conclusion. Kidd et al. (2018) had people who were previously cited for not using a belt and reported not regularly using a belt drive a vehicle with an intermittent seat belt reminder for 1 week and then drive a vehicle with the same reminder or a gearshift interlock the following week. The gearshift interlock significantly increased the rate of driver belt use by 16% across the study weeks compared with participants who only drove vehicles with the intermittent reminder. A follow-on study using a similar method found that a speed-limiting interlock increased the rate of driver belt use 33% relative to the same intermittent reminder (Kidd and Singer 2019b). However, the increase in driver belt use observed for the speed-limiting interlock was similar to the 30% and 34% increase observed for a seat belt reminder that lasted 100 seconds and one that did not end until the driver buckled, respectively.

Seat belt interlock system acceptance

Seat belt interlocks are generally perceived as intrusive and unacceptable (Eby et al. 2005; TRB 2003). In a recent national survey, respondents were asked whether they would support or oppose using various types of seat belt interlocks for increasing seat belt use (Kidd et al. 2014b). About one-third of respondents who reported not always using a belt and one-fifth who reported never using a belt said they would support different types of interlock systems. Only around half of respondents who reported always using their seat belt said the same. Kidd et al. also found that only one-third of respondents who did not always use their seat belt thought interlocks were acceptable for encouraging belt use while nearly twice as many thought chimes, warning lights, or physical reminders were acceptable for increasing belt use. Dahlstedt (1999) interviewed 435 Swedish drivers who were observed not using a seat belt about their attitudes toward seat belt use and technologies to increase belt use. When asked if they would borrow or rent a car with a powerful buzzer as a seat belt reminder or a gearshift interlock, about one-fifth said they would refuse a car with the interlock compared with only 2% that would refuse a car with a powerful buzzer.

Attitudes toward interlocks expressed by respondents in past surveys are naïve. Seat belt interlock systems may become more acceptable once people have had a chance to experience them. Bao et al. (2020) found that people who did not always use a seat belt recognized the safety value of a speed-limiting interlock or gearshift interlock and found the technologies easy to use. People who briefly experienced different seat belt interlock systems and reminder systems while driving on a closed course reported similar levels of acceptance for each technology (Kidd and Singer 2019b). Drivers who drove a vehicle with a gearshift interlock or speed-limiting interlock for 1 week were more supportive of using the technology for increasing seat belt use than drivers who drove a similar vehicle without the technology for 1 week (Kidd et al. 2018; Kidd and Singer 2019b).

Ideally, interlock systems would only inconvenience people who do not routinely use a belt, but buckling routines vary (Kidd et al. 2014b). Most drivers buckle up before the vehicle is moving (Malenfant and Van Houten 2008), and many buckle before shifting into gear (McGehee et al. 2022). McGehee et al. (2022) found that drivers buckled after shifting into gear on nearly one-quarter of day-to-day drives that were recorded for about a month. Routine belt users who buckle up after shifting into gear may find the inconvenience of a gearshift interlock unacceptable.

Disrupting vehicle use or limiting its function may create unique safety concerns that also undermine the acceptance of seat belt interlock systems. Kidd and Singer (2019b) found that almost every participant who briefly drove a vehicle with a speed-limiting interlock or gearshift interlock described a safety concern with the technology. People were concerned that restricting speed would be problematic in an emergency, would disrupt traveling on the highway, or increase crash risk. Participants who drove a vehicle with a seat belt interlock for multiple weeks in a field study raised similar safety concerns (Bao et al. 2020).

Inconveniences, safety concerns, and general nonacceptance may lead people to circumvent seat belt interlock systems and undermine the positive effects on seat belt use. In Kidd and Singer (2019b) study, 44% of people who did not routinely use a belt circumvented the speed-limiting interlock system in their vehicle; only 21% of participants circumvented a persistent or incessant seat belt reminder. Thirty-eight percent of nonroutine belt users in Kidd et al. (2018) study circumvented the gearshift interlock system. A smaller proportion of participants (17%) in Bao et al.’s study (2020) circumvented one of the seat belt interlock systems on at least some trips.

Requirements worldwide

Requirements for seat belt reminder systems throughout the world are summarized in Table A1 of the Appendix. Many consumer information organizations follow Euro NCAP’s current or former requirements for seat belt reminder systems. Euro NCAP (2022) currently requires front-row seat belt reminders to have multiple warning periods including a final audible signal lasting at least 90 seconds with no more than 10 seconds of separation between signals. A 60-second visual signal showing second- and third-row seating positions with an unbuckled seat belt is required at ignition along with a shorter 30-second audible signal when an unbelted rear occupant is detected or a rear occupant unbuckles their belt.

Table 1. Estimated seat belt use rate for front and rear occupants if every U.S. vehicle was equipped with 100-second audible seat belt reminder in 2020.

Seating position	Observed belt use rate	Seat belt reminder system effectiveness	Estimated belt use rate
Front row	90.3%^a	29.6%^b	93.2%
Rear row	80.0%^a	29.6%^b	85.9%

^aObserved daytime belt use rates from Enriquez (2021).

^bEstimate from Kidd and Singer (2019b).

Euro NCAP’s current requirements were adopted by the Australasian NCAP (2022). Latin American and Caribbean NCAP (Latin NCAP 2020) adopted a slightly older version with similar requirements (Euro NCAP 2018). The New Car Assessment Program for Southeast Asia’s (ASEAN NCAP 2019) requirements are similar to Euro NCAP’s current requirements but permit longer gaps between audible signals (25 sec vs. 10 sec). Global NCAP (2021), which focuses on pushing vehicle safety forward in emerging markets like India and Africa, adopted the oldest Euro NCAP (2013) requirements and allows longer 25-second gaps between audible signals and a single, immediate audible signal and 30-second visual reminder when a rear occupant is unbuckled. China NCAP’s requirements closely align with Euro NCAP’s current requirements, but, unlike other organizations, China NCAP penalizes vehicles that do not meet their requirements instead of awarding credit to those that do (China Automotive Technology and Research Center Co. and Ltd 2021).

The United Nations Economic Commission for Europe (UNECE) World Forum for Harmonization of Vehicle Regulations developed U.N. Regulation No. 16, which set type approval requirements for seat belt reminder systems (UNECE 2022). The requirements are consistent with many of Euro NCAP’s requirements, but the required minimum duration of the audible signal is shorter (30 seconds) than Euro NCAP’s current requirements (90 seconds). Japan NCAP’s (2020) requirements are similar to U.N. Regulation No. 16. Korean NCAP offers an optional seat belt reminder assessment that provides additional credit toward an overall vehicle rating (CARHS GMBH 2022).

The U.S. only requires a reminder for the driver’s seat at ignition, requires a short audible signal, and does not require a notification when a seat belt is unbuckled. Canada adopts many U.S. FMVSS, and its Technical Standards Document 208 is identical to FMVSS 208 (Transport Canada 2018). The Insurance Institute for Highway Safety (IIHS 2021) evaluates seat belt reminder systems for first- and second-row seating positions in new U.S. vehicles. The highest ratings are given to vehicles with a persistent audible and visual reminder lasting at least 90 seconds when a front-row occupant is unbelted, that provide information about second-row seat belt use at ignition, and that have an audible and visual reminder lasting at least 30 seconds when a second-row seat belt is unbuckled. Consistent with other organizations worldwide, IIHS specifies requirements to ensure that audible and visual reminders begin in a timely manner, audible reminders stand out from background vehicle cabin noise, and visual warnings are easily seen by the driver.

Estimated increase in belt use and lives saved

Kidd and Singer (2019b) found that a seat belt reminder system with an audible reminder lasting 100 seconds increased the belt use of drivers who did not always use their seat belt by nearly 30%. If every vehicle in the U.S. had an audible reminder that increased belt use by almost 30% at each seating position, then daytime belt use in the U.S. would be expected to increase by about 3 percentage points from 90.3% to 93.2% in the front row and by about 6 percentage points from 80% to 85.9% in the rear row (Table 1).

In 2020, 9,629 front row occupants older than 15 years and 746 second- and third-row occupants older than 7 years who died in a motor vehicle crash were unrestrained. Seat belts could have potentially saved about 5,500 of these occupants (Table 1). Hence, if every vehicle in the U.S. had a persistent audible reminder lasting 100 seconds that increased the belt use of front- and rear-row occupants by nearly 30% then about 1,600 lives could be saved each year (Table 2).

Discussion

FMVSS 208 does not require new vehicles to be equipped with vehicle technology proven to increase belt use. Legislative changes from MAP-21 granted NHTSA the opportunity to strengthen FMVSS 208 by requiring more stringent reminders or allowing vehicle manufacturers to install interlocks as a means for meeting a safety standard. This study reviewed the latest research on seat belt reminders and interlocks to support revisions to FMVSS 208.

Existing studies have consistently found that audible reminders exceeding FMVSS 208 requirements and lasting longer than 8 seconds were effective for increasing seat belt use. More recent research suggests that persistent audible reminders lasting at least 90 seconds are the most effective and increase driver seat belt use by 30% or more. Several studies have shown that various types of interlocks ranging from ignition interlocks to speed-limiting interlocks also are effective for increasing driver seat belt use. However, the evidence is mixed on whether interlocks are more effective for increasing belt use than reminders lasting at least 100 seconds.

Table 2. Estimated potential number of front- and rear-occupant lives saved if every U.S. vehicle was equipped with a persistent 100-second audible seat belt reminder system in 2020.

Seating position	Vehicle type	Unbelted deaths	Fatality risk reduction from restraint use	Potential lives saved by restraint use	Seat belt reminder system effectiveness	Potential lives saved by persistent seat belt reminders
Front row^a	Passenger car	5,018	45%^c	2,258	29.6%^e	668
	Light trucks and vans	4,611	60%^c	2,767	29.6%^e	819
	Total	9,629		5,025	29.6%^e	1,487
Rear row^b	Passenger car	435	58%^d	252	29.6%^e	75
	Light trucks and vans	311	75%^d	233	29.6%^e	69
	Total	746		486	29.6%^e	144
Overall		10,375		5,511		1,631

Notes. Counts are rounded to the nearest whole number. Unbelted deaths are based on analysis of 2020 Fatality Analysis Reporting System data.

^aFront-row occupants older than 15 years.

^bSecond- and third-row occupants older than 7 years.

^cEstimate from Kahane (2000).

^dEstimate from Kahane (2017).

^eEstimate from Kidd and Singer (2019b).

Technologies that motivate occupants to use a belt must be effective for increasing belt use but also acceptable to consumers. Negative consumer reaction to seat belt interlock systems drove legislation that curtailed NHTSA’s ability to require more stringent vehicle technology for increasing belt use. Several recent national surveys suggest acceptance of interlocks remains lower than acceptance of seat belt reminders. Every passenger vehicle sold in the U.S. since the 1970s is required to have a seat belt reminder system, which may bolster acceptance of reminders. Experience with seat belt interlock technology has been shown to foster more positive opinions of the technology, but existing studies have highlighted the potential for seat belt interlocks to inconvenience routine belt users, create safety concerns, and increase willingness by some to avoid or circumvent the technology. Furthermore, no organization in the world requires or encourages seat belt interlock systems to be equipped in new vehicles. Together, the extant literature and current regulatory environment indicates that acceptance continues to be a barrier for seat belt interlocks.

Existing U.S. federal requirements for seat belt reminder systems are weak compared with requirements in other parts of the world. In addition to requiring longer-lasting audible reminders, almost every regulatory or consumer information organization throughout the world requires seat belt reminder systems for front-row and second-row seating positions. Many also require seat belt reminders for third-row seating positions. Research on using technology to increase rear-occupant belt use is sparse, but existing research suggests that reminders from the vehicle or other sources increases rear-occupant belt use. The effectiveness of using seat belt interlocks for increasing rear-occupant belt use has not been investigated.

The current study estimated changes in daytime belt use rate and the annual number of lives that could be saved by providing a persistent audible reminder at each seating position in every U.S. vehicle. The estimated change in belt use rate and number of lives saved assume that the effect of a persistent audible reminder observed for drivers who do not always use a belt (Kidd and Singer 2019b) would be observed for unbuckled occupants at every seating position in every vehicle. The accuracy of these assumptions cannot be determined, but the change in belt use rate and lives saved estimates reported in this study provide a reasonable measure of the potential safety benefits of requiring persistent seat belt reminders at each seating position in every vehicle.

Persistent seat belt reminder systems that last at least 90 seconds like those required by IIHS and in other countries have the potential to save hundreds of lives each year in the U.S. More persistent seat belt reminders may save even more lives in modern vehicles that are equipped with belt technologies such as crash tensioners that snug the belt and force limiters that reduce the force exerted on the chest of restrained occupants. Based on this literature review, there is sufficient empirical evidence, successful exemplars from other regulatory and consumer information organizations throughout the world, and a clear and sizeable potential public health benefit for strengthening FMVSS 208 to require more persistent seat belt reminders at every seating position in new U.S. vehicles.

Acknowledgments

The authors would like to thank Thierry Mousel for his assistance with summarizing seat belt reminder system requirements around the world, Eric Teoh for his assistance with revising the manuscript, and Jessica Jermakian for reviewing prior versions of the manuscript.

Additional information

Funding

This work was supported by the Insurance Institute for Highway Safety.