Comparison of reporting of seat belt use by police and crash investigators: variation in agreement by injury severity

Purpose: To evaluate agreement between police and trained investigators regarding seat belt use by crash victims, according to injury severity. Methods: We used data from the National Accident Sampling System Crashworthiness Data System (CDS) for front seat occupants, 16 years and older, in crashes during 1993–2000. Crashworthiness Data System investigators determined belt use from vehicle inspection, interviews, and medical record information; their assessment was considered the gold standard for this analysis. Occupant severity of injury was categorized in five levels from no injuries to death. We estimated the sensitivity, specificity, and area under receiver operating characteristic curves for police reports of belt use. Results: Among 48,858 occupants, sensitivity of a police report that a belt was used was 95.8% overall and varied only modestly by injury severity. Specificity of a police report that a belt was not used was 69.1% overall; it was the lowest among the uninjured (53.2%) and greatest among the dead (90.4%). The area under the curve was 0.82 (95% confidence interval 0.82–0.83) overall; this was lowest among those not injured (0.75, 95% confidence interval 0.74–0.76) and increased with injury severity to 0.91 (95% confidence interval 0.90–0.93) among those who died. Conclusion: Police usually classify belted crash victims as belted, regardless of injury severity. But they often classify unbelted survivors as belted when they were not. This misclassification may result in exaggerated estimates of seat belt effectiveness in some studies.     

Seat belt use and accident involvement: A comparison of driving behavior before and after a seat belt law

In an earlier study, researchers at the University of North Carolina Highway Safety Research Center found drivers classified as seat belt nonusers on the basis of direct observation and self-reported belt use to be overrepresented in prior accidents and violations. This study represents a follow-up and extension of the earlier study where accident and violation rates over a 2.5-year interval following the classification by seat belt use status are compared. Seat belt nonusers were again found to be overrepresented in both accidents and violations. In other analyses of these data, changes in seat belt use status were found not to be associated with changes in accident or violation rates, and seat belt use rates reported by police in accidents following the mandatory seat belt law greatly exceeded both the observed and self-reported use rates. This was especially pronounced for drivers who responded that they rarely or never used seat belts.     

Impact of safety belt use on road accident injury and injury type in Kuwait

The enactment of Kuwait's seat belt law in January 1994 provided an opportunity to examine the impact of seat belt use on road accident fatalities and injury types in this affluent Persian Gulf nation. Via a structured data form, the results of injurious/fatal road accidents for more than 1200 accident victims were gathered from the files of the six major government hospitals which treat most traffic accident victims. Statistical analysis of the data showed that seat belt use has had a positive effect in reducing both road traffic fatalities and multiple injuries in Kuwait. The use of seat belts has also affected the nature of the injuries resulting from road traffic accidents. Non-users of belts experienced higher frequencies of head, face, abdominal and limb injuries. Users of belts, on the other hand, suffered higher frequencies of neck and chest injuries. The interrelationship between the victim, his age, and the type of injuries resulting from road traffic accidents is also investigated.     

Seat belt utilization in Saudi Arabia and its impact on road accident injuries

Most industrialized countries and many developing countries have passed laws that require the use of seat belts in motor vehicles. It is widely believed that seat belt use is an effective way to reduce road accident fatalities and injuries. Saudi Arabia joined these countries when it enacted a similar law on 5 December 2000 making seat belt use compulsory for all drivers and front-seat passengers. This study measures seat belt use rate and its impact on the number of road accident injuries during the first few months that followed the enactment of the law. It also investigates drivers' behaviour and personal characteristics and their relationship with using seat belts by using a questionnaire specially prepared for this purpose. Results show that seat belt use rate in two Riyadh suburbs were 33% and 87%, respectively, for drivers and 4% and 41%, respectively, for front-seat passengers (FSP's). Such belt use rates are considered low yet encouraging when compared with use rates before enacting the law. Results also show that there was a significant drop in certain types of injuries due to traffic accidents after the enactment of the seat belt law. Questionnaire results show that certain personal characteristics were correlated with seat belt use rate. Finally, implications of these findings in terms of future plans for improving traffic safety are discussed.     

Extra enforcement and the use of seat belts by drivers in Illinois

The use of seat belts by drivers was measured in three target and three control cities in Illinois before, during, and after the application of heightened police enforcement of the seat belt law in the target cities. The extra enforcement produced increases in the use of seat belts by drivers during the four months of the heightened enforcement. Observations of seat belt use continued for four months after the end of the enforcement, and a substantial residual effect remained in two of the three target cities. In one target city the use of seat belts had dropped close to the level at the start of the project by the end of the second month after the end of enforcement. Taking account of the percentage of drivers who became aware of the increased enforcement suggested that a sustained program of enforcement may result in 60%–70% of drivers using seat belts.     

Estimating seat belt effectiveness using matched-pair cohort methods

Using US data for 1986-1998 fatal crashes, we employed matched-pair analysis methods to estimate that the relative risk of death among belted compared with unbelted occupants was 0.39 (95% confidence interval (CI) 0.37-0.41). This differs from relative risk estimates of about 0.55 in studies that used crash data collected prior to 1986. Using 1975-1998 data, we examined and rejected three theories that might explain the difference between our estimate and older estimates: (1) differences in the analysis methods; (2) changes related to car model year; (3) changes in crash characteristics over time. A fourth theory, that the introduction of seat belt laws would induce some survivors to claim belt use when they were not restrained, could explain part of the difference in our estimate and older estimates; but even in states without seat belt laws, from 1986 through 1998, the relative risk estimate was 0.45 (95% CI 0.39-0.52). All of the difference between our estimate and older estimates could be explained by some misclassification of seat belt use. Relative risk estimates would move away from 1, toward their true value, if misclassification of both the belted and unbelted decreased over time, or if the degree of misclassification remained constant, as the prevalence of belt use increased. We conclude that estimates of seat belt effects based upon data prior to 1986 may be biased toward 1 by misclassification.     

How would increasing seat belt use affect the number of killed or seriously injured light vehicle occupants?

The expected effects of increasing seat belt use on the number of killed or seriously injured (KSI) light vehicle occupants have been estimated for three scenarios of increased seat belt use in Norway, taking into account current seat belt use, the effects of seat belts and differences in crash risk between belted and unbelted drivers. The effects of seat belts on fatality and injury risk were investigated in a meta-analysis that is based on 24 studies from 2000 or later. The results indicate that seat belts reduce both fatal and non-fatal injuries by 60% among front seat occupants and by 44% among rear seat occupants. Both results are statistically significant. Seat belt use among rear seat occupants was additionally found to about halve fatality risk among belted front seat occupants in a meta-analysis that is based on six studies. Based on an analysis of seat belt wearing rates among crash involved and non-crash involved drivers in Norway it is estimated that unbelted drivers have 8.3 times the fatal crash risk and 5.2 times the serious injury crash risk of belted drivers. The large differences in crash risk are likely to be due to other risk factors that are common among unbelted drivers such as drunk driving and speeding. Without taking into account differences in crash risk between belted and unbelted drivers, the estimated effects of increasing seat belt use are likely to be biased. When differences in crash risk are taken into account, it is estimated that the annual numbers of KSI front seat occupants in light vehicles in Norway could be reduced by 11.3% if all vehicles had seat belt reminders (assumed seat belt wearing rate 98.9%), by 17.5% if all light vehicles had seat belt interlocks (assumed seat belt wearing rate 99.7%) and by 19.9% if all front seat occupants of light vehicles were belted. Currently 96.6% of all (non-crash involved) front seat occupants are belted. The effect on KSI per percentage increase of seat belt use increases with increasing initial levels of seat belt use. Had all rear seat occupants been belted, the number of KSI front seat occupants could additionally be reduced by about 0.6%. The reduction of the number of KSI rear seat occupants would be about the same in terms of numbers of prevented KSI.     

Availability, functionality, and use of seat belts in Beijing taxis prior to the 2008 Beijing Olympic Games

Use of driver seat belts and availability and functionality of passenger seat belts in a convenience sample of 231 Beijing taxis were examined in the months prior to the 2008 Beijing Olympic Games. Driver and front passenger seat belt use was mandated in China from 2004 to help address the growing public health crisis of road trauma. Results from observations made by in-vehicle passengers revealed that 21.2% of drivers were correctly wearing a belt, approximately half were not, and one third were using the belt in a non-functional way. Over 3/4 of this sample of taxi drivers were unrestrained while working. The percentage of functionally available belts was higher for front than rear passengers (88.3% and 22.9%, respectively). This low rate of belt availability in rear seats calls into question the preparedness of the fleet to cater for the safety needs of foreign visitors to China, particularly those from countries with high levels of restraint use. Factors influencing the use/misuse of seat belts in China remain largely unexplored. Results of this pilot study support further investigations of barriers to using injury prevention mechanisms such as seat belts in less motorised countries.     

An evaluation of the effectiveness of forward facing child restraint systems

The objective of this study was to determine the effectiveness of forward facing child restraint systems (FFCRS) in preventing serious injury and hospitalization to children 12-47 months of age as compared with similar age children in seat belts. Data were obtained from a cross-sectional study of children aged 12-47 months in crashes of insured vehicles in 15 states, with data collected via insurance claims records and a telephone survey. Effectiveness estimates were limited to those children between 12 and 47 months of age seated in the back row(s) of vehicles, restrained in FFCRS, regardless of misuse, or seat belts of all types and usage. Completed survey information was obtained on 1207 children, representing 12632 children in 11619 crashes between 1 December 1998 and 31 May 2002. Serious injuries occurred to 0.47% of all 12-47-month olds studied, including 1.72% of those in seat belts and 0.39% of those in child restraint systems. The risk of serious injury was 78% lower for children in FFCRS than in seat belts (odds ratio (OR) = 0.22, 95% confidence interval (CI) = 0.11-0.45, P = 0.001). The risk of hospitalization was 79% lower for children in FFCRS than in seat belts (OR = 0.21, 95% CI = 0.09-050, P = 0.001). There was no difference between the restraint types in preventing minor injuries. As compared with seat belts, CRS are very highly effective in preventing serious injuries and hospitalization, respectively. This effectiveness estimate is substantially higher than older estimates, demonstrating the benefits of current CRS designs. These results provide those educating parents and caregivers population-based data on the importance of child restraint use.     

Method to evaluate the effect of safety belt use by rear seat passengers on the injury severity of front seat occupants

Although the effectiveness of seat belts for reducing injury to rear seat passengers in traffic accidents has been well documented, the ratio of rear-seat passengers restrained by seatbelts remains lower than that of drivers or passengers in front seats. If passengers in rear seats do not wear seat belts, they may sustain unexpected injury to themselves when involved in accidents, and also endanger front occupants (drivers or front seat passengers). This paper focuses on the tendency of front seat occupants to sustain severer injuries due to forward movement of passengers in rear seats at the moment of frontal collisions, and evaluates the effectiveness of rear passengers' wearing seat belts in reducing injuries of front seat occupants. Since the occurrence of occupant injuries depends considerably on the crash severity, we proposed to use pseudo-delta V in regression analysis to represent velocity change during a collision when analyzing statistical accident data. As the crash severity can be estimated from pseudo-delta V, it becomes possible to make appropriate estimations even when the crash severity differs in data. The binary model derived from the ordered response model was used to evaluate the influence on the injury level based on pseudo-delta V, belted or unbelted status, gender and age. Occupants in cars with a hood in the case of car-to-car frontal collisions were extracted from the statistical data on accidents in Japan. Among 81,817 cars, where at least one passenger was present, a total of 6847 cars in which all passengers sustained injuries and which had at least one rear seat passenger aboard were analyzed. The number of killed or seriously injured drivers is estimated to decrease by around 25% if rear seat occupants come to wear seat belts. Also, the number of killed or seriously injured passengers in front seats is estimated to decrease by 28% if unbelted rear seat occupants come to wear seat belts. Thus, wearing of seat belts by previously unbelted rear seat passengers is considered effective in reducing not only injuries to the rear seat passengers themselves but also injuries to front seat occupants.     

Shoulder belts in motor vehicle crashes: a statewide analysis of restraint efficacy

The purpose of our study was to evaluate the impact of shoulder belt use on motor vehicle crash ejection, morbidity and mortality. We analyzed motor vehicle crash records linked to hospital inpatient data for front seat occupants of passenger cars in Utah between 1994 and 1996 (n = 103,035). Stochastic simulations were used to adjust for possible seatbelt misclassification. There were 276 (0.3%) occupants coded as using only a shoulder belt. The adjusted odds of ejection for shoulder only belted occupants was higher compared to lap-shoulder belted (odds ratio (OR) = 18.9; 95% confidence interval (CI) = 15.1, 25.1) and lap only belted occupants (OR = 4.3; 95% Cl = 2.9, 7.7). There was no difference in the odds of ejection for an occupant using a shoulder belt only and an occupant using no seatbelt (OR = 1.1; 95% CI = 1.0, 1.3). Occupants using a shoulder belt only were more likely to sustain a fatal or hospitalizing injury than lap-shoulder belted (OR = 2.3; 95% Cl = 1.9, 3.0), and lap only belted occupants (OR = 1.8; 95% CI = 1.3, 2.7), while controlling for other covariates. Occupants using only a shoulder belt had the same odds of a fatal or hospitalizing injury as unbelted occupants (OR = 1.1; 95% Cl = 0.9, 1.4). Average hospital inpatient length of stay, charges and injury severity scores were similar for all restraint types. These results stress the need for the use of a lap belt in conjunction with the shoulder belt.     

Attitudes of commercial motor vehicle drivers towards safety belts

Despite the fact that Hawaii has one of the highest seat belt use rates for passenger vehicles in the United States, and has had a mandatory seat belt use law since the 1980s, studies have shown that commercial motor vehicles (CMV) seat belt use rates are low. To better understand this phenomenon, a comprehensive survey of commercial vehicle drivers was conducted in Hawaii to ascertain attitudes and self-reported behaviors regarding seat belt use. A total of 791 drivers responded to a written questionnaire implemented at weigh stations and distributed to various trucking firms and transport centers. Approximately 67% reported that they use seat belts “always” when driving a CMV (commercial motor vehicle), yet when asked how often do other CMV drivers use seat belts, only 31% responded “always.” Interestingly, 86% of these same drivers reported that they use seat belts “always” when driving a personal vehicle. The major reason cited for non-use of belts was “frequent stops/inconvenience” (29%), and “not safety conscious” (23%). Notably, the self-reported use of safety belts is highest among operators of vans (88% said “always”), followed by buses (87% said “always”) and lowest among truck drivers (only 60% said “always”). In this paper, some of the differences between self-reported users and non-users are explored and a multivariate logit model was developed to predict the odds of belt use as a function of various factors.     

The use of generalized estimating equations in the analysis of motor vehicle crash data

The purpose of this study was to determine if it is necessary to use generalized estimating equations (GEEs) in the analysis of seat belt effectiveness in preventing injuries in motor vehicle crashes. The 1992 Utah crash dataset was used, excluding crash participants where seat belt use was not appropriate (n=93,633). The model used in the 1996 Report to Congress [Report to congress on benefits of safety belts and motorcycle helmets, based on data from the Crash Outcome Data Evaluation System (CODES). National Center for Statistics and Analysis, NHTSA, Washington, DC, February 1996] was analyzed for all occupants with logistic regression, one level of nesting (occupants within crashes), and two levels of nesting (occupants within vehicles within crashes) to compare the use of GEEs with logistic regression. When using one level of nesting compared to logistic regression, 13 of 16 variance estimates changed more than 10%, and eight of 16 parameter estimates changed more than 10%. In addition, three of the independent variables changed from significant to insignificant (alpha=0.05). With the use of two levels of nesting, two of 16 variance estimates and three of 16 parameter estimates changed more than 10% from the variance and parameter estimates in one level of nesting. One of the independent variables changed from insignificant to significant (alpha=0.05) in the two levels of nesting model; therefore, only two of the independent variables changed from significant to insignificant when the logistic regression model was compared to the two levels of nesting model. The odds ratio of seat belt effectiveness in preventing injuries was 12% lower when a one-level nested model was used. Based on these results, we stress the need to use a nested model and GEEs when analyzing motor vehicle crash data.     

Determinants of motor vehicle deaths in the United States: a cross-sectional analysis.

This paper uses 1987 state-level data and least-squares regression to estimate a model of motor vehicle deaths in the United States. The model includes several factors accounted for in previous cross-sectional studies of these fatalities. The estimates suggest that income, the ratio of urban to rural driving, expenditures on highway police and safety, motor vehicle inspection laws, and adult seat belt use laws with secondary enforcement provisions are inversely related to motor vehicle death rates. They also indicate that volume of driving, speed, speed variance, driving density, alcohol consumption, temperature, and a dummy variable for western states are directly related to the rates.     

A joint econometric analysis of seat belt use and crash-related injury severity

This paper formulates a comprehensive econometric structure that recognizes two important issues in crash-related injury severity analysis. First, the impact of a factor on injury severity may be moderated by various observed and unobserved variables specific to an individual or to a crash. Second, seat belt use is likely to be endogenous to injury severity. That is, it is possible that intrinsically unsafe drivers do not wear seat belts and are the ones likely to be involved in high injury severity crashes because of their unsafe driving habits. The preceding issues are considered in the current research effort through the development of a comprehensive model of seat belt use and injury severity that takes the form of a joint correlated random coefficients binary-ordered response system. To our knowledge, this is the first instance of such a model formulation and application not only in the safety analysis literature, but in the econometrics literature in general. The empirical analysis is based on the 2003 General Estimates System (GES) data base. Several types of variables are considered to explain seat belt use and injury severity levels, including driver characteristics, vehicle characteristics, roadway design attributes, environmental factors, and crash characteristics. The results, in addition to confirming the effects of various explanatory variables, also highlight the importance of (a) considering the moderating effects of unobserved individual/crash-related factors on the determinants of injury severity and (b) seat belt use endogeneity. From a policy standpoint, the results suggest that seat belt non-users, when apprehended in the act, should perhaps be subjected to both a fine (to increase the chances that they wear seat belts) as well as mandatory enrollment in a defensive driving course (to attempt to change their aggressive driving behaviors).     

Geographic and sociodemographic variation in self-reported seat belt use in the United States

Background

With new data available, we sought to update existing literature on the prevalence of self-reported seat belt use by state, region, and rural/urban status and to estimate the strength of the association between seat belt use and rural/urban status adjusted for type of seat belt law and several other factors.

Methods

We examined data on self-reported use of seat belts from 50 states, the District of Columbia, and three territories using the 2008 Behavioral Risk Factor Surveillance System, a state-based random-digit-dialed telephone survey (n = 406,552). Reported seat belt use was assessed by state, U.S. Census regions, and U.S. Department of Agriculture (USDA) rural/urban continuum codes.

Results

Overall, 85% of adults in the United States reported they always used seat belts. Regionally, the West had the highest prevalence of persons who reported that they always wear seat belts (89.6%) and the Midwest had the lowest (80.4%). States with primary seat belt laws had the highest prevalence of reported seat belt use, compared with states with secondary or no laws. After adjusting for various sociodemographic characteristics, body mass index, and type of seat belt law, persons in the most densely populated metropolitan areas were significantly more likely to report always wearing seat belts than those in most sparsely populated rural areas (adjusted odds ratio = 2.9).

Conclusion

Our findings reinforce the evidence that primary enforcement seat belt laws are effective for increasing seat belt use, and suggest that upgrading to primary enforcement laws will be an important strategy for reducing crash-related fatalities in rural areas.     

The influence of damage distribution on serious brain injury in occupants in frontal motor vehicle crashes

In spite of improvements in motor vehicle safety systems and crashworthiness, motor vehicle crashes remain one of the leading causes of brain injury. The purpose of this study was to determine if the damage distribution across the frontal plane affected brain injury severity of occupants in frontal impacts. Occupants in "head on" frontal impacts with a Principal Direction of Force (PDOF) equal to 11, 12, or 1o'clock who sustained serious brain injury were identified using the Crash Injury Research Engineering Network (CIREN) database. Impacts were further classified based on the damage distribution across the frontal plane as distributed, offset, and extreme offset (corner). Overall, there was no significant difference for brain injury severity (based on Glasgow Coma Scale<9, or brain injury AIS>2) comparing occupants in the different impact categories. For occupants in distributed frontal impacts, safety belt use was protective (odds ratio (OR)=0.61) and intrusion at the occupant's seat position was four times more likely to result in severe (Glasgow Coma Scale (GCS)<9) brain injury (OR=4.35). For occupants in offset frontal impacts, again safety belt use was protective against severe brain injury (OR=0.25). Possibly due to the small number of brain-injured occupants in corner impacts, safety belts did not significantly protect against increased brain injury severity during corner impacts. This study supports the importance of safety belt use to decrease brain injury severity for occupants in distributed and offset frontal crashes. It also illustrates how studying "real world" crashes may provide useful information on occupant injuries under impact circumstances not currently covered by crash testing.     

The seat belt syndrome in children

Lap belts, fitted to the centre seats of Australian cars for the past 22 years, have come under criticism as being injurious to children. The weight of evidence is that lap belts provide substantial protection, though less than three-point belts. A specific injury, the seat belt syndrome (SBS), to abdominal viscera and/or lumbar spine has been particularly associated with lap belts, an association confirmed by a hospital-based study in Melbourne. Roadside observations of belt use and Transport Accident Commission claims permitted the calculation of the incidence of SBS and the relative risks of SBS by seated position. The centre rear seat (lap belt) carried about twice the risk of SBS as outboard rear seats (three-point belts), which in turn have 2.7 times the risk of the outboard front seat. The number of SBS cases in Victoria has increased with penetration of the car fleet by 1971 and later cars. Suggestions are made for improvements in the restraint system.     

Predictors of safety belt use among crash-involved drivers and front seat passengers: adjusting for over-reporting

Police-reported crash data are rarely used to investigate safety belt use and its predictors, even though these data have a number of advantages over data collected in roadside surveys. It has been widely recognized that motorists tend to over-report their safety belt use to police when mandatory belt use becomes law. In this paper, we use a logistic regression model that allows for misclassification errors in outcome variable to examine predictors of safety belt use among crash-involved drivers and front seat passengers. Our analysis shows significant associations between occupant characteristics, driving circumstances, and safety belt use. Alcohol involvement has the strongest negative association with safety belt use, but this association would be considerably underestimated without adjusting for the over-reporting of safety belt use in police-reported crash data. The adjusted belt use rate among front seat occupants with at least nonincapacitating injuries is about 81%, compared to 90% in police-reported crash data.     

Injuries to belted older children in motor vehicle crashes

Context

The American Academy of Pediatrics and the National Highway Traffic Safety Administration currently recommend that, unless they are under 57 in. in height, 8–12-year-old children use seat belts and all should ride in the rear seats of vehicles. These recommendations assume that the vehicle seat belt should provide adequate protection for these older children in the event of a crash.

Objectives

To describe characteristics of older children in the rear seat using seat belts in crashes, to estimate their risk and body region distribution of injury, and to identify risk factors for injury.

Methods

A representative sample of 6680 seat belt-restrained occupants, 8–12 years of age, seated in the rear seat during crashes involving insured vehicles in 16 US states between December 1998 and December 2007. A telephone interview was conducted with the driver of each vehicle. The main outcome was the parent-reported injury defined as Abbreviated Injury Scale (AIS) 2 or greater injuries.

Results

The risk of injury for belted 8–12 year olds in the rear seat was 1.3%. Head injury was the most common injury (60%), followed by injuries to the face (9%), upper extremity (9%) and abdomen (9%). One out of five (21%) 8–12 year olds either did not use the shoulder portion of the vehicle seat belt or placed it incorrectly behind their back or under their arm. Bivariate analyses indicated a higher risk of injury for these children (1.8%) as compared to children using both the lap and shoulder portions of the seat belt (1.1%). However, this difference was not statistically significant when other risk factors such as crash severity and characteristics of the driver were considered.

Conclusions

Injuries to the head, face, abdomen and upper extremity are the most common injuries to target for improved protection among 8–12 year olds in seat belts. Driver and crash characteristics are important risk factors for injury. A recent federal motor vehicle safety standard requiring lap and shoulder belts in all rear seat positions has the potential to further decrease the risk of injury to older children using seat belts.