Seat belts

Overview

Seat belts saved an estimated 14,955 lives in 2017. For drivers and front-seat passengers, using a lap and shoulder belt reduces the risk of fatal injury by 60 percent in an SUV, van or pickup and by 45 percent in a car.

If everyone buckled up, an additional 2,456 deaths could have been prevented. While the vast majority of drivers and front-seat passengers use seat belts, nearly half of people who die in crashes are not belted.

Belt laws increase belt use, especially with publicized enforcement. Belt use rates are higher in states with primary enforcement laws, which allow police to stop a driver solely for not using a seat belt. In states with secondary enforcement, police can only enforce the belt law if they have pulled over the driver for another violation first.

Latest news

Better belt reminders would save lives

Persistent audible belt reminders are no less effective than interlocks and may raise fewer concerns for drivers, new research suggests.

April 25, 2019

Better restraints needed in back seat

A new study of crashes in which belted rear-seat passengers were killed or seriously injured suggests better restraint systems are needed.

April 25, 2019

Why belts matter

Lap and shoulder belts prevent ejection from the vehicle and keep people from colliding with the vehicle interior during a crash. They are also designed to manage forces on the body.

Even though a vehicle may have slowed or stopped after colliding with another vehicle or object, unbelted occupants keep moving at the same travel speed until they catch up with and crash into what's in front of them. Seat belts help to prevent or reduce injuries from this second collision by securing people to their seats so they slow down with the vehicle as its crush zone absorbs most of the kinetic energy associated with the vehicle and the occupant's precrash motion. The longer people "ride down" a crash, the less likely they are to be injured.

Worn properly, seat belts are designed to spread crash forces across the stronger bony parts of the body, including the shoulder, rib cage and pelvis. Seat belts also prevent occupants from being ejected from the vehicle, an event associated with high risk of injury and death. Relative to occupants who are not ejected from vehicles, occupants who are ejected in nonrollover crashes are nearly twice as likely to die, and those who are ejected in rollover crashes are 4 times more likely to die (NHTSA, 2010).

Unbelted occupants can put other people in the vehicle at risk. In a frontal crash, drivers and front-seat passengers are at increased risk of injury from unbelted back-seat passengers, and in a side-impact crash, passengers sitting adjacent to unbelted passengers are at increased risk of injury.

Exposure to unbelted occupants increases the risk of injury or death to other occupants in the vehicle by 40 percent (MacLennan et al., 2004). In a frontal crash, an unbelted rear seat passenger sitting behind a belted driver increases the risk of fatality for the driver by 137 percent compared with a belted rear seat passenger (Bose et al., 2013).

In both the front seat and the back seat, seat belts reduce the risk of serious injury or death in a crash. Research has shown a 45 percent reduction in the risk of a fatal injury to front-seat car occupants when lap and shoulder belts are used (NHTSA, 2017). The risk of a moderate to critical injury is reduced by half. For people in front seats of SUVs, vans and pickups, the use of lap and shoulder belts reduces the risk of a fatal injury by 60 percent and a moderate to critical injury by 65 percent. 

In the center rear seat, lap and shoulder belts reduce the risk of fatal injury by 58 percent in cars and 75 percent in SUVs, vans, and pickups (Kahane, 2017).

The National Highway Traffic Safety Administration (NHTSA) estimates that seat belts saved the lives of 14,955 people in 2017 and more than 69,000 lives during the five-year period from 2013 through 2017 (National  Center  for  Statistics  and  Analysis, 2019). An additional 2,549 lives could have been saved in 2017 if all passenger vehicle occupants older than age 4 had used seat belts.

What if a seat belt doesn't fit or has only a lap belt?


For seat belts to do their job, it's important that they fit right. That's why it is so critical for children who have outgrown their forward-facing child restraints to use belt-positioning boosters.

A properly fitted shoulder belt should lie snugly across the center of the chest and shoulder, not on the neck or face or falling off the shoulder. The lap belt should lie snugly across the upper thighs or low on the hips, not the belly.

When shopping for a new vehicle, try on the seat belts to see whether they are a good fit for you and the other passengers who will be riding in the vehicle. In many vehicles, belts can be customized for a better fit. For example, adjustable D-rings allow shoulder belts to be raised or lowered as needed. Ask your dealer or consult the vehicle manual for more information. If your seat belt is not long enough, it may be possible to lengthen it with a belt extender from your vehicle manufacturer.

A properly fitting belt offers the best protection, but any restraint is better than none at all.

Similarly, a lap belt alone is better protection than no belt in a crash. Today's vehicles have three-point belts in all seating positions, but vehicle built before September 2007 may only have lap belts in the rear center seats (NHTSA, 2004).

In a study of potentially fatal crashes involving back-seat occupants age 5 and older, lap belts reduced the risk of fatal injury for outboard occupants by 32 percent in cars and 63 percent in vans and SUVs (Morgan, 1999). Although lap-only belts weren't as effective as lap and shoulder belts, particularly in frontal crashes, using lap-only belts provided more protection than being unrestrained.

Belt use

Nationwide observed seat belt use in 2018 was 90 percent for drivers and 89 percent for right-front seat passengers (Enriquez & Pickrell, 2019). Belt use is lower in the back seat: 75 percent of rear-seat occupants were observed using belts in 2017 compared with 90 percent of front-seat occupants (Li & Pickrell, 2019).

Fewer than half of passenger vehicle drivers (49 percent) and passengers (43 percent) ages 13 and older killed in 2017 were using belts. Only 28 percent of fatally injured back seat occupants ages 13 and older were using belts.

Belt use rates are lower among fatally injured occupants than among the general population because risk of death is much higher when not using a seat belt. Plus, people who don't use belts tend to be riskier drivers.

The 2018 observed belt use rate among front-seat occupants was about 6 times the rate observed in 1983 (90 percent vs. 14 percent) (Enriquez & Pickrell, 2019; Transportation Research Board, 2003). The following chart shows the changes in belt use during this time period.

Seat belt use is lower among younger people and males. In 2017, 87 percent of 16-24 year-olds in the front seat were observed using their belts, compared with 90 percent of ages 25-69 and 91 percent of those 70 and older (Li & Pickrell, 2019). Ninety-two percent of female front-seat occupants were observed using their belts, compared with 88 percent of males.

Observed belt use in 2018 was lowest among occupants of pickups (84 percent), compared with occupants of cars (90 percent), vans and SUVs (92 percent) (Enriquez & Pickrell, 2019).

Research also shows that belt use is lower among occupants of older vehicles and among drivers who have been drinking alcohol (Mackay, 1997; Partyka, 1989).

In an analysis of 10 years of data on belt use among fatally injured occupants, use was consistently about 18 percentage points lower at night than during the day (Tison et al., 2010). Nighttime unbelted drivers have more previous traffic violations and criminal arrests than nighttime belted drivers and daytime drivers (belted or unbelted) (Thomas et al., 2010).

A national telephone survey conducted by the Institute in 2012 found the top reasons for not using seat belts among people who used belts some but not all of the time included driving a short distance, forgetfulness, and discomfort (Kidd et al., 2014). Among people who never used seat belts, the top reasons for not using them were discomfort, the belief that it's not necessary, and a dislike of being told what to do.

Another national survey in 2016 found the top reason for adults not using belts in the rear was that they perceived the back seat to be safer than the front (Jermakian & Weast, 2018).

Laws

With the exception of New Hampshire, all states and the District of Columbia require adult front-seat occupants to use seat belts. Adult rear-seat passengers also are covered by the laws in 29 states and the District of Columbia.

Thirty-four states and the District of Columbia have primary enforcement. Primary enforcement laws allow a police officer to stop and cite a motorist solely for not using a seat belt. In states with secondary enforcement, police can only enforce the law if the motorist has been pulled over for another violation first.

Seat belt and child restraint laws by state, in detail

Primary enforcement laws are more effective at getting people to buckle up. In 2018, observed front-seat occupant belt use rates were 5 percentage points higher in states with primary enforcement than in other states (91 vs. 86 percent) (Enriquez & Pickrell, 2019).

Based on drivers' self-reports, the frequency of never using a seat belt was twice as high in states with secondary enforcement compared with states with primary enforcement laws (Beck & Shults, 2009). States that went from secondary to primary enforcement laws saw a 14-percentage-point median increase in observed belt use (Shults et al., 2004).

Systematic literature reviews show that both primary and secondary laws reduce deaths and nonfatal injuries, but primary laws have the greater effect (Dinh-Zarr et al., 2001; Rivara et al., 1999). The incremental effect of primary versus secondary laws on fatalities is estimated at 3-14 percent (Dinh-Zarr et al., 2001).

Institute research has shown that switching from a secondary law to a primary law reduces passenger vehicle driver deaths by 7 percent (Farmer & Williams, 2005). Based on this research, if all states that still had secondary laws in 2017 had switched to primary laws, 254 lives could have been saved that year. 

Secondary enforcement originally came about because legislators in some states were reluctant to enact primary laws because of concerns that police would use the law to harass minorities (Farmer & Williams, 2005). However, several studies found that changing from secondary to primary enforcement resulted in proportionally equal or fewer tickets for minorities (Preusser et al., 2005; Solomon et al., 2000; Solomon et al., 2001). 

Laws also vary by whether they require belt use in the back seat.

In states that require belt use in all seating positions, 84 percent of back-seat passengers were observed using seat belts in 2017, compared with 63 percent of back-seat passengers in states that require only front-seat belt use (Li & Pickrell, 2019).

Higher fines for seat belt violations also are associated with higher rates of observed belt use and higher rates of belt use among fatally injured front-seat occupants. An increase in fines from $25 to $60 was associated with 3-4 percentage point increases in belt use, while increasing fines from $25 to $100 was associated with 6-7 percentage point increases (Nichols et al., 2010).

Numerous studies show that publicized enforcement campaigns such as "Click It or Ticket" are needed to sustain high levels of compliance over time (Williams et al., 2000). In 1993, North Carolina implemented the first statewide "Click It or Ticket" campaign. Institute research found that driver belt use increased from 64 percent before the campaign to 80 percent after the first three-week enforcement period (Williams et al., 1996).

Most states allow adults to ride unrestrained in pickup beds, which are designed to carry cargo and offer no protection in a crash. People can be easily ejected from cargo areas at relatively low speeds as a result of a sharp turn to avoid an obstacle or crash.

Thirty states and D.C. have laws regarding the practice. Most of those laws restrict children in cargo areas, but many contain exceptions.

Belt reminders and interlocks

Federal safety standards require a belt reminder system for drivers that provides a warning light and an audible warning lasting 4-8 seconds. However, reminders that short aren't effective (Geller et al., 1980; Robertson & Haddon, 1974).

Most vehicle manufacturers equip their vehicles with enhanced belt reminder systems that provide longer visual or audible reminders. The most persistent of these have been shown to be highly effective.

A study involving part-time belt users who had recently received a citation for failing to wear a seat belt found that an indefinite audible reminder or one that lasted 100 seconds increased belt use by about a third (Kidd & Singer, 2019).

Federal safety standards do not currently require belt reminders in the back seat. However, in 2012 Congress instructed NHTSA to begin rulemaking to require them. 

In the U.S. market, Volvo was the first manufacturer to alert the driver when back-seat passengers didn't buckle up. Some additional manufacturers have equipped some of their vehicle models with reminder systems that detect seat belt use for back-seat passengers, but most vehicles sold in the U.S. are not equipped with this feature.

In a 2012 Institute survey, more than three-quarters of drivers supported belt reminders that would alert them when children in back seats aren't buckled (Kidd & McCartt, 2014).

Interlocks, which limit vehicle function if the driver and front-seat passenger aren't buckled, are another technology that can boost belt use. However, they have a controversial past.

Congress passed a law banning seat belt interlocks in the 1970s. That was after the National Highway Traffic Safety Administration required them on all vehicles without airbags.

A 2012 highway reauthorization law relaxed these restrictions. Now NHTSA can permit automakers to equip vehicles with belt interlocks as an alternative means to comply with a federal safety standard.

In the IIHS study involving part-time belt users, a speed-limiting interlock that held the vehicle speed to 15 mph during unbelted driving was just as effective as the persistent reminders, increasing belt use by 33 percent (Kidd & Singer, 2019). A gearshift interlock increased belt use by 16 percent, though the change wasn't statistically significant.

The study found that drivers were easily able to circumvent the interlocks — for example, by sitting on the belt or buckling it behind their back. In addition, some participants raised safety concerns about limiting vehicle function or being unable to drive the vehicle in an emergency.

A national telephone survey found that 70 percent of part-time belt users and 44 percent of non-users said they would be more likely to buckle up with ignition interlocks. However, only 30 percent of part-time belt users and 16 percent of non-users thought ignition interlocks to increase seat belt use would be acceptable in their vehicles (Kidd et al., 2014).

Seat belt technology

Seat belts have become more sophisticated in recent decades. Belts in the front seat are engineered to work in coordination with airbags to keep a person in the proper position and help manage forces on the body. Embedded devices called crash tensioners cause the belt to tighten around occupants immediately when a crash occurs. To reduce the risk of chest injuries, belts also have force limiters, which allow some webbing to spool out before forces from the belt get too high.

Most belts in the rear seat lack crash tensioners and force limiters.

Some manufacturers have equipped rear seating positions with inflatable belts. These belts aim to reduce head, neck and chest injuries by deploying over the occupant's torso and shoulder during a crash so that crash forces are distributed to an area of the body 5 times larger than with conventional seat belts. When vehicle sensors determine that a severe collision is occurring, the belt's airbag fills with cold compressed gas and expands sideways across the occupant's body. The inflatable belt operates like a conventional seat belt for everyday use.