The effectiveness of electronic stability control in reducing real-world crashes: a literature review

OBJECTIVE: Electronic stability control (ESC) is designed to help drivers maintain heading control of their vehicles in high-speed or sudden maneuvers and on slippery roads. The wider proliferation of ESC across the vehicle fleet has allowed evaluation of its effects in real-world crashes in many countries, including Japan, Germany, Sweden, France, Great Britain, and the United States. This article provides a summary of the findings. METHODS: Studies that examined the real-world effectiveness of ESC were reviewed. Crash effects have been examined for different roadways, using differing analytic methods, different crash severities, and different make/model vehicles including both cars and SUVs. The review discusses the methodological differences and examines the findings according to vehicle type, crash type and severity, and road conditions. RESULTS: The overwhelming majority of studies find that ESC is highly effective in reducing single-vehicle crashes in cars and SUVs. Fatal single-vehicle crashes involving cars are reduced by about 30-50% and SUVs by 50-70%. Fatal rollover crashes are estimated to be about 70-90% lower with ESC regardless of vehicle type. A number of studies find improved effectiveness in reducing crashes when road conditions are slippery. There is little or no effect of ESC in all multi-vehicle crashes; however, there is a 17-38% reduction in more serious, fatal multi-vehicle crashes. CONCLUSIONS: Given the extraordinary benefits of ESC in preventing crashes, especially those with more serious outcomes, the implementation of ESC should be accelerated to cover the full range of passenger vehicles in both developed and developing markets.     

Crash risk of ESC-fitted passenger cars

Objective: We examined both fatal and injury at-fault crashes of a population of passenger cars fitted with electronic stability control (ESC). Crash rates were calculated in relation to both registration years and mileage. Crash rates were also calculated for a non-ESC car population and crash rate ratios were calculated to compare the crash risk between ESC-fitted and non-ESC-fitted passenger cars.

Methods: Passenger car models with and without ESC were identified (ESC-equipped cars: 3,352,813 registration years; non-ESC-equipped: 5,839,946 registration years) and their vehicle information for the period 2009–2013, including mileage (ESC-equipped vehicles: 89.3 billion kilometers; non-ESC-equipped: 72.4 billion kilometers), was drawn from the national Vehicular and Driver Data Register.

The registry of Finnish road accident investigation teams was accessed and all fatal at-fault crashes among the cars in the study populations (ESC 97; non-ESC 377) for the period 2009–2013 were analyzed. The motor insurance database includes at-fault crashes leading to injuries and was utilized for analyses (ESC: N?=?8,827, non-ESC: N?=?21,437).

Crash rates and crash rate ratios were calculated to evaluate crash risk of both ESC-equipped and non-ESC-equipped passenger cars. Poisson regression was used to model crash involvement rate ratios both per registration year and per mileage for vehicles with ESC and without ESC, controlling for age and gender of the vehicle owner and vehicle mass.

Results: Passenger cars fitted with ESC showed lower crash rates than non-ESC-equipped cars in all crash types studied. In general, the difference in crash rates between ESC-equipped and non-ESC-equipped vehicles was greater when the crashes were compared to the mileage rather than registration years. The mileage-proportional crash rate of ESC-equipped cars was 64% (95% confidence interval, 61%; 67%) lower in run-off-road crashes resulting in injury and as much as 82% (65%; 91%) lower in fatal run-off-road crashes when suicides and disease attacks were not taken into account.

Conclusions: Our results show that modern passenger cars provide a significant crash risk reduction, which depends on both ESC and passive safety features introduced. Results also show that exposure evaluation in terms of registration years (or vehicle population) instead of true mileage can provide an overly pessimistic view of the crash risk.     

Effects of electronic stability control: an update

OBJECTIVE: An earlier study reported that electronic stability control (ESC) in passenger vehicles reduced single-vehicle crash involvement risk by 41% and single-vehicle fatal crash involvement risk by 56%. The purpose of the present study was to update these effectiveness estimates using an additional year of crash data and a larger set of vehicle models. METHODS: The amount of data increased by half, allowing for separate effectiveness estimates for cars and sport utility vehicles (SUVs) and a more detailed examination of multiple-vehicle crash types. Crash involvement rates per registered vehicle were compared for otherwise identical vehicle models with and without ESC. RESULTS: Based on all police-reported crashes in 10 states during three years, ESC reduced single-vehicle crash involvement risk by approximately 41%. Effects were significantly higher for SUVs than for cars. ESC reduced single-vehicle crash involvement risk by 49% for SUVs and 33% for cars. Based on all fatal crashes in the United States during four years, ESC was found to have reduced single-vehicle fatal crash involvement risk by 56%. Again, effectiveness estimates were higher for SUVs than for cars--59% for SUVs and 53% for cars, but these differences were not statistically significant. Multiple-vehicle fatal crash involvement risk was reduced by 32%-37% for SUVs and 25% for cars. CONCLUSIONS: The present study confirms the results of the earlier study. There are significant reductions in single-vehicle crash rates when passenger vehicles are equipped with ESC. In addition, ESC leads to reductions in severe multiple-vehicle crashes.     

Forward collision warning system impact

Abstract

Objective: The objective of this research is to use historical crash data to evaluate the potential benefits of both high- and low-speed automatic emergency braking (AEB) with forward collision warning (FCW) systems.

Methods: Crash data from the NHTSA’s NASS–General Estimates System (GES) and Fatality Analysis Reporting System (FARS) databases were categorized to classify crashes by the speed environment, as well as to identify cases where FCW systems would be applicable.

Results: Though only about 19% of reported crashes occur in environments with speeds greater than 45?mph, approximately 32% of all serious or fatal crashes occur in environments with speeds greater than 45?mph. The percentage of crashes where FCW systems would be relevant has remained remarkably constant, varying between about 21 and 26% from 2002 to 2015. In 2-vehicle fatal crashes where one rear-ends the other, the fatality rates are actually higher in the struck vehicle (33%) than the striking vehicle (26%). The disparity is even greater when considering size–class differences, such as when a light truck rear-ends a passenger car (15 vs. 42% fatality rates, respectively).

Conclusions: NHTSA and the Insurance Institute for Highway Safety (IIHS) proposed the Automatic Emergency Braking Initiative in 2015, which is intended to make AEB (also called crash-imminent braking) with FCW systems standard on nearly all new cars by September 2022. Twenty automakers representing 99% of the U.S. auto market voluntarily committed to the initiative. Though the commitment to safety is laudable, the AEB component of the agreement only covers low-speed AEB systems, with the test requirements set to 24?mph or optionally as low as 12?mph. The test requirements for the FCW component of the agreement include 2 tests that begin at 45?mph. Only 21% of relevant serious injury or fatal accidents occur in environments at speeds under 24?mph, whereas about 22% of serious or fatal crashes occur in environments with speeds greater than 45?mph. This means that the AEB with FCW systems as agreed upon will cover only 21% of serious or fatal crashes and will not cover 22% of serious or fatal crashes. Because these systems are protective not only for the occupants of the vehicle where they are installed but also other vehicles on the roads, the data indicate that these systems should be a standard feature on all cars for high-speed as well as low-speed environments for the greatest social benefit.     

Impact of primary safety belt laws on alcohol-related front-seat occupant fatalities: five case studies

OBJECTIVE: Impaired drivers and other high-risk road users are less likely to use their safety belts, thus increasing the risk of fatal injury in the event of a crash. Although safety belt laws have been shown to increase wearing rates for daytime non-crash-involved drivers and their front-seat passengers, little evidence is available on the effect these laws have on belt usage by crash-involved drinking drivers and their passengers. METHODS: This study evaluated the influence of primary safety belt law upgrades from secondary laws on front-seat occupants of passenger cars driven by drinking drivers in fatal crashes in five states: California, Illinois, Maryland, Michigan, and Washington. The outcome measures used to evaluate these law upgrades were (1) the change in safety belt usage rates of front-seat occupants in passenger cars driven by drinking drivers in fatal crashes and (2) the change in alcohol-related front-seat occupant fatalities in passenger cars driven by drinking drivers. RESULTS: Four of the five states demonstrated increases in safety belt use by front-seat occupants of passenger cars of drinking drivers in fatal crashes following the upgrade to primary safety belt laws. Three states (California, Michigan, and Washington) experienced significant reductions in the number of front-seat occupant fatalities in vehicles driven by drinking drivers. CONCLUSIONS: The adoption of primary law upgrades was associated with significant increases in safety belt use (four of five states) and significant reductions in fatalities among high-risk occupants (i.e., front-seat occupants involved in fatal crashes in vehicles driven by drinking drivers) in three of the five states studied.     

The effectiveness of ESP (Electronic Stability Program) in reducing real life accidents

ESP (Electronic Stability Program) has recently been introduced onto the market in an effort to reduce the number and severity of loss-of-control automobile accidents. This reduction is expected to be particularly evident for accidents on roads with low friction (e.g., wet or icy conditions). This study aimed to evaluate the statistical effectiveness of ESP using data from accidents that occurred in Sweden during 2000 to 2002. To control for exposure, induced exposure methods were used, where ESP-sensitive to ESP-insensitive accidents and road conditions were matched in relation to cars equipped with and without ESP. Cars of similar, or in some cases identical, make and model were used to isolate the role of ESP. As predicted, the study showed a positive effect of ESP in circumstances where road surfaces have low friction. The overall effectiveness was 22.1 (+/-21) percent, while for accidents on wet roads, the effectiveness increased to 31.5 (+/-23.4) percent. On roads covered with ice and snow, the corresponding effectiveness was 38.2 (+/-26.1) percent. In addition, ESP was found to be effective for three different types of cars: small front-wheel drive; large front-wheel drive; and large rear-wheel drive.     

Adjusting for car occupant injury liability in relation to age, speed limit, and gender-specific driver crash involvement risk

It is well established that older drivers' fragility is an important factor associated with higher levels of fatal crash involvement for older drivers. There has been less research on age-related fragility with respect to the sort of minor injuries that are more common in injury crashes. This study estimates a quantity that is related to injury fragility: the probability that a driver or a passenger of that driver will be injured in crashes involving two cars. The effects of other factors apart from drivers' fragility are included in this measure, including the fragility of the passengers, the crashworthiness of cars driven, seatbelt use by the occupants, and characteristics of crashes (including configuration and impact speed). The car occupant injury liability estimates appropriately includes these factors to adjust risk curves by age, gender, and speed limit accounting for overrepresentation in crashes associated with fragility and these other factors.     

The effectiveness of lane departure warning systems—A reduction in real-world passenger car injury crashes

Objective: The objective of this study was to estimate the safety benefits of in vehicle lane departure warning (LDW) and lane keeping aid (LKA) systems in reducing relevant real-world passenger car injury crashes.

Methods: The study used an induced exposure method, where LDW/LKA-sensitive and nonsensitive crashes were compared for Volvo passenger cars equipped with and without LDW/LKA systems. These crashes were matched by car make, model, model year, and technical equipment; that is, low-speed autonomous emergency braking (AEB) called City Safety (CS). The data were extracted from the Swedish Traffic Accident Data Acquisition database (STRADA) and consisted of 1,853 driver injury crashes that involved 146 LDW-equipped cars, 11 LKA-equipped cars, and 1,696 cars without LDW/LKA systems.

Results: The analysis showed a positive effect of the LDW/LKA systems in reducing lane departure crashes. The LDW/LKA systems were estimated to reduce head-on and single-vehicle injury crashes on Swedish roads with speed limits between 70 and 120 km/h and with dry or wet road surfaces (i.e., not covered by ice or snow) by 53% with a lower limit of 11% (95% confidence interval [CI]). This reduction corresponded to a reduction of 30% with a lower limit of 6% (95% CI) for all head-on and single-vehicle driver injury crashes (including all speed limits and all road surface conditions).

Conclusions: LDW/LKA systems were estimated to lower the driver injury risk in crash types that the systems are designed to prevent; that is, head-on and single-vehicle crashes. Though these are important findings, they were based on a small data set. Therefore, further research is desirable to evaluate the effectiveness of LDW/LKA systems under real-world conditions and to differentiate the effectiveness between technical solutions (i.e., LDW and LKA) proposed by different manufacturers.     

Characteristics of vehicle-animal crashes in which vehicle occupants are killed

During the past 10 years almost 1,500 people have been killed in motor vehicle collisions with animals. Police reports on 147 fatal vehicle-animal crashes during 2000-2002 were obtained from nine states. The goal was to determine common crash types, types of animals involved, and steps that could be taken to reduce the crashes and injuries. Seventy-seven percent of the struck animals were deer, but six other types of animals were involved including small ones such as dogs. Eighty percent of the crashes were single-vehicle events. In most of these cases a motorcycle struck an animal and the rider came off the vehicle, or a passenger vehicle struck an animal and then ran off the road; in a few cases the animal went through the windshield. Multiple-vehicle crashes included vehicles striking deer that went through the windshields of oncoming vehicles, vehicles striking animals and then colliding with other vehicles, and vehicles striking animals that subsequently were struck by other vehicles. Crashes occurred primarily in rural areas, on roads with 55 mph or higher speed limits, during evening or nighttime hours, and in darkness. Greater application of deer-vehicle collision countermeasures known to be effective is needed, but it is noteworthy that a majority of fatalities occurred from subsequent collisions with other vehicles or objects, not from animal contacts. Sixty-five percent of motorcyclists killed were not wearing helmets, and 60% of vehicle occupants killed were unbelted; many of these fatalities would not have occurred with proper protection.     

The estimated reduction in the odds of loss-of-control type crashes for sport utility vehicles equipped with electronic stability control

INTRODUCTION: Using data from the NASS General Estimates System (GES), the method of induced exposure was used to assess the effects of electronic stability control (ESC) on loss-of-control type crashes for sport utility vehicles. METHOD: Sport utility vehicles were classified into crash types generally associated with loss of control and crash types most likely not associated with loss of control. Vehicles were then compared as to whether ESC technology was present or absent in the vehicles. A generalized additive model was fit to assess the effects of ESC, driver age, and driver gender on the odds of loss of control. In addition, the effects of ESC on roads that were not dry were compared to effects on roads that were dry. RESULTS: Overall, the estimated percentage reduction in the odds of a loss-of-control crash for sport utility vehicles equipped with ESC was 70.3%. Both genders and all age groups showed reduced odds of loss-of-control crashes, but there was no significant difference between males and females. With respect to driver age, the maximum percentage reduction of 73.6% occurred at age 27. The positive effects of ESC on roads that were not dry were significantly greater than on roads that were dry.     

Using medico-legal data to investigate fatal older road user crash circumstances and risk factors

Objective: This study used medico-legal data to investigate fatal older road user (ORU, aged 65 years and older) crash circumstances and risk factors relating to 4 key components of the Safe System approach (e.g., roads and roadsides, vehicles, road users, and speeds) to identify areas of priority for targeted prevention activity.

Method: The Coroners' Court of Victoria's (CCOV) Surveillance Database was searched to identify and describe the frequency and rate per 100,000 population of fatal ORU crashes in the Australian state of Victoria for 2013–2014. Information relating to the deceased ORU, crash characteristics and circumstances, and risk factors was extracted and analyzed.

Results: One hundred and thirty-eight unintentional fatal ORU crashes were identified in the CCOV Surveillance Database. Of these fatal ORU crashes, most involved older drivers (44%), followed by older pedestrians (32%), older passengers (17%), older pedal cyclists (4%), older motorcyclists (1%), and older mobility scooter users (1%). The average annual rate of fatal ORU crashes per 100,000 population was 8.1 (95% confidence interval [CI], 6.0–10.2). In terms of the crash characteristics and circumstances, most fatal ORU crashes involved a counterpart (98%), of which the majority were passenger cars (50%) or fixed/stationary objects (25%), including trees (46%) or embankments (23%). In addition, most fatal ORU crashes occurred close to home (73%), on-road (87%), on roads that were paved (94%), on roads with light traffic volume (37%), and during low-risk conditions: between 12 p.m. and 6 p.m. (44%), on weekdays (80%), during daylight (75%), and under dry/clear conditions (81%). Road user (RU) error was identified by the police and/or the coroner for the majority of fatal crashes (55%), with a significant proportion of deceased ORUs deemed to have failed to yield (54%) or misjudged (41%).

Conclusions: RU error was the most significant factor identified in fatal ORU crashes, which suggests that there is a limited capacity of the road system to fully accommodate RU errors. Initiatives related to safer roads and roadsides, vehicles, speed zones, as well as behavioral approaches are key areas of priority for targeted activity to prevent fatal ORU crashes in the future.     

Factors contributing to serious and fatal injuries in belted rear seat occupants in frontal crashes

Abstract

Objectives: Earlier research has shown that the rear row is safer for occupants in crashes than the front row, but there is evidence that improvements in front seat occupant protection in more recent vehicle model years have reduced the safety advantage of the rear seat versus the front seat. The study objective was to identify factors that contribute to serious and fatal injuries in belted rear seat occupants in frontal crashes in newer model year vehicles.

Methods: A case series review of belted rear seat occupants who were seriously injured or killed in frontal crashes was conducted. Occupants in frontal crashes were eligible for inclusion if they were 6 years old or older and belted in the rear of a 2000 or newer model year passenger vehicle within 10 model years of the crash year. Crashes were identified using the 2004–2015 National Automotive Sampling System Crashworthiness Data System (NASS-CDS) and included all eligible occupants with at least one Abbreviated Injury Scale (AIS) 3 or greater injury. Using these same inclusion criteria but split into younger (6 to 12 years) and older (55+ years) cohorts, fatal crashes were identified in the 2014–2015 Fatality Analysis Reporting System (FARS) and then local police jurisdictions were contacted for complete crash records.

Results: Detailed case series review was completed for 117 rear seat occupants: 36 with Maximum Abbreviated Injury Scale (MAIS) 3+ injuries in NASS-CDS and 81 fatalities identified in FARS. More than half of the injured and killed rear occupants were more severely injured than front seat occupants in the same crash. Serious chest injury, primarily caused by seat belt loading, was present in 22 of the injured occupants and 17 of the 37 fatalities with documented injuries. Nine injured occupants and 18 fatalities sustained serious head injury, primarily from contact with the vehicle interior or severe intrusion. For fatal cases, 12 crashes were considered unsurvivable due to a complete loss of occupant space. For cases considered survivable, intrusion was not a large contributor to fatality.

Discussion: Rear seat occupants sustained serious and fatal injuries due to belt loading in crashes in which front seat occupants survived, suggesting a discrepancy in restraint performance between the front and rear rows. Restraint strategies that reduce loading to the chest should be considered, but there may be potential tradeoffs with increased head excursion, particularly in the absence of rear seat airbags. Any new restraint designs should consider the unique needs of the rear seat environment.     

Car safety and social differences in traffic injuries among young adult drivers: a study of two-car injury-generating crashes in Sweden

Objective—The study examines whether socioeconomic and sex differences in road-traffic crashes leading to injury vary according to car-safety level.Method—Individuals records of subjects born 1970–1972 registered in the Swedish Census of 1985 (n = 334,070) are linked to road-traffic-crash data for the period 1988–2000 for first police-registered two-car crashes leading to severe or fatal injury (n = 4875). Injuries are split into categories according to level of car safety on a five-point scale, based on criteria related to crash safety. Account is taken of both how the car is constructed and the effectiveness of its safety equipment (such as airbags and seat belts). For each car-safety level, relative risks are computed considering socioeconomic groups of origin, educational level, and sex.Results—No substantial differences between drivers in different socioeconomic positions of origin is observed except for crashes involving cars 30% better than average with regard to safety. There are consistent risk differences across all car-safety categories according to educational level. Male drivers show an elevated risk of injury in all car categories, except for cars with the poorest safety where they are at significant under-risk.Conclusions—Car-safety level impacts on social differences in road-traffic injury risks in specific and restricted manners. Car-safety development is an important factor in improved road safety, but it may not benefit all to the same extent.     

The Crash Compatibility of Cars and Light Trucks

This paper investigates the compatibility of cars, light trucks, and vans (LTVs) involved in traffic crashes. An analysis of U.S. crash statistics shows that, although LTVs currently account for approximately one–third of registered U.S. passenger vehicles, collisions between cars and LTVs account for over one–half of all fatalities in light vehicle–to–vehicle crashes. In these crashes, 81 percent of the fatally injured are found to be occupants of the car. These statistics suggest that LTVs and passenger cars are incompatible in traffic crashes, and that LTVs are the more aggressive of the two vehicle classes. The fundamental incompatibility between cars and LTVs is observed even when the analysis is restricted to collisions between vehicles of model year 1990 or later - indicating that, despite the availability of newer safety countermeasures, e.g., airbags, the incompatibility between cars and LTVs will persist in future fleets. Through examination of crash test results, field crash statistics, and vehicle measurements, the paper explores the design imbalances between cars and LTVs, e.g., mass, stiffness, and geometry, which lead to these severe crash incompatibilities.     

Differences in Long-term Medical Consequences Depending on Impact Direction Involving Passenger Cars

Objective: There is limited knowledge of the long-term medical consequences for occupants injured in car crashes in various impact directions. Thus, the objective was to evaluate whether injuries leading to permanent medical impairment differ depending on impact direction.

Methods: In total, 36,743 injured occupants in car crashes that occurred between 1995 and 2011 were included. All initial injuries (n = 61,440) were classified according to the Abbreviated Injury Scale (AIS) 2005. Injured car occupants were followed for at least 3 years to assess permanent medical impairment. The data were divided into different groups according to impact direction and levels of permanent impairment. The risk of permanent medical impairment was established for different body regions and injury severity levels, according to AIS.

Results: It was found that almost 12% of all car occupants sustained a permanent medical impairment. Given an injury, car occupants involved in rollover crashes had the highest overall risk to sustain a permanent medical impairment. Half of the head injuries leading to long-term consequences occurred in frontal impacts. Far-side occupants had almost the same risk as near-side occupants. Occupants who sustained a permanent medical impairment from cervical spine injuries had similar risk in all impact directions (13%) except from rollover (17%). However, these injuries occurred more often in rear crashes. Most of the injuries leading to long-term consequences were classified as minor injuries by AIS for all impact directions.

Conclusions: Studying crash data from a perspective of medical impairment is important to identify injuries that might not be prioritized only considering the AIS but might lead to lower quality of life for the occupant and also costs for society. These results can be used for road transport system strategies and for making priority decisions in vehicle design.     

Intersection AEB implementation strategies for left turn across path crashes

Abstract

Objective: Left turn across path with traffic from the opposite direction (LTAP/OD) is the second most frequent car-to-car intersection crash type after straight crossing path (SCP) in Germany and the United States. Intersection automated emergency braking (AEB) for passenger cars can address these crashes.

This study investigates 2 implementation strategies of intersection AEB addressing LTAP/OD crashes: (1) only the turning car is equipped with an intersection AEB and (2) turning and straight-heading cars are equipped with an intersection AEB. For each strategy, the influence of a safety zone around the vehicles that should not be entered is evaluated in terms of accident avoidance, injury mitigation, and change in velocity (delta-V) of remaining accidents. Results are given as a function of market penetration.

Methods: A total of 372 LTAP/OD crashes from the time series precrash matrix (PCM), a subsample of the German In-Depth Accident Study (GIDAS), were resimulated in the PRediction of Accident Evolution by Diversification of Influence factors in COmputer simulation (PRAEDICO) simulation framework. A Kudlich-Slibar rigid-body impact model and an injury risk curve derived from GIDAS were used to predict remaining moderate to fatal (Maximum Abbreviated Injury Scale [MAIS] 2?+?F) injuries among car occupants.

Results: With a safety zone of 0.2 m, when the turning vehicle only was equipped with an intersection AEB, 59% of the crashes were avoided at a 100% market penetration. With both vehicles equipped the percentage increased to 77%. MAIS 2?+?F injured occupants were reduced by 60 and 76%, respectively. Considering both the turning and the straight-heading vehicles, the delta-V decreased strongly with market penetration in remaining left-side impacts but only slightly in remaining frontal and right-side impacts. Eliminating the safety zone substantially decreases effectiveness in all conditions.

Conclusions: Implementation strategy and safety zone definition strongly influence the real-life performance of intersection AEB. AEB should be applied not only for the turning vehicle but also for the straight-going vehicle to benefit from the full potential. Situationally appropriate safety zone definitions, in line with human hazard perception, need more attention and are a key to balance true positive and false positive performance. Remaining delta-V does not decrease broadly; hence, there is no evidence that future LTAP/OD crashes will be generally of lower severity. This highlights the need for continuous development of in-crash protection.     

Rollover injury: effects of near- and far-seating position, belt use, and number of quarter rolls

PURPOSE: Vehicle and occupant responses in rollovers are complex since many factors influence both. This study analyzes the following factors: 1) belt use, 2) seated position with respect to the lead side in the rollover, 3) another front occupant in the crash, and 4) number of quarter rolls. The aim was to improve our understanding of rollover injury mechanisms. METHOD: Rollover accidents were analyzed using 1992-2004 NASS-CDS data. The sample included adult drivers and right-front passengers. All occupants were evaluated and then a subset of non-ejected occupants was analyzed. Using roll direction and seating position, the sample was divided into near- and far-seated occupants. Injury and fatality risks were determined by seatbelt use, occupancy, rollover direction, and number of quarter rolls. Risk was defined as the number of injured (e.g., MAIS 3+) divided by the number of exposed occupants (MAIS 0-6). Significance in differences was determined. A matched-pair analysis was used to determine the risk of serious injury for near- and far-seated occupants who were either belted or unbelted in the same crash. RESULTS: For all occupants, serious injury risks were highest for far-seated, unbelted occupants at 18.1% +/- 4.8%, followed by near-seated unbelted occupants at 12.0% +/- 3.5%. However, the difference was not statistically significant. Belted near- and far-seated occupants had a similar injury risk of 4.3% +/- 1.2% and 4.0% +/- 1.2%, respectively. For non-ejected occupants, serious injury risk was 9.5% +/- 3.2% for far-seated unbelted occupants and 4.9% +/- 2.1% for near-seated unbelted occupants, not a statistically significant difference. Serious injury risk was similar for belted near- and far-seated non-ejected occupants, at 3.6% +/- 1.1%. Seatbelts were 64.2%-77.9% effective in preventing serious injury for all occupants and 62.1%-26.5% for far- and near-seated, non-ejected occupants, respectively. Based on the matched pairs, seatbelts were less effective for near-seated (5.0%) compared to far-seated (2.8%) occupant MAIS 3+F risks. This was similar for non-ejected occupants. An unbelted near-seated occupant increased the risk for a belted far-seated occupant by 2.2 times, whereas an unbelted far-seated occupant increased the risk for a belted near-seated occupant by 10.2 times. For all occupants, the risk of serious injury increased with the number of quarter rolls, irrespective of seated position. For near-seated occupants, seatbelt effectiveness was higher in < or =1 roll than 1+ roll, at 72.3% compared to 28.3%. For far-seated occupants, seatbelt effectiveness was similar in < or =1 and 1+ roll samples at 78.3% and 76.8%, respectively. Near-seated occupants had the lowest serious injury risk when they were the sole occupant in the vehicle. This was also true for non-ejected occupants. However, far-seated occupants had a lower injury risk when another occupant was involved in the crash. CONCLUSIONS: The effect of carrying another occupant appears to reduce the risk of serious injury to far-seated occupants. However, near-seated occupants are better off being the sole occupant in the vehicle. Seatbelt effectiveness was lowest at 28.3% for non-ejected, near-seated occupants in 1+ rolls. This finding deserves further evaluation in an effort to improve seatbelt effectiveness in rollovers. For belted drivers alone in a rollover, fatality risks are 2.24 times higher for the far- versus near-seated position. Analysis of rollovers by quarter turns indicates that occupants are both far-side and near-side in rollovers. The extent to which this confounds the relationship between roll direction, seating position, and injury risk is unknown.     

Safety belt effectiveness in preventing driver fatalities versus a number of vehicular, accident, roadway, and environmental factors

Safety belt effectiveness in preventing fatalities to drivers is examined versus a number factors (vehicle, accident, and environmental) by applying the double-pair comparison method to appropriate subsets of the Fatal Accident Reporting System (FARS) data. For each of 13 factors studied, safety belt effectiveness (the percent of fatally injured unbelted drivers who would not have been killed if they had been wearing safety belts) is estimated, as is an associated standard error of the estimate. The results, which are presented graphically, provide no evidence that safety belt effectiveness is systematically influenced by most of the factors investigated, including car mass and model year. The absence of any systematic relationship with car mass is in agreement with an earlier finding based on the pedestrian fatality exposure method; this agreement adds plausibility to the assumptions used for both the earlier and the present methods. Safety belt effectiveness is greater for single-car crashes (62 ± 5) % than for crashes involving two cars (30 ± 8) % , this difference being statistically significant at p<.02. The results suggest weakly that safety belt effectiveness is greater for two-door (48 ± 6) % than for four-door (38 ± 10) % cars, and is greater for striking (44 ± 6) % cars than for struck (27 ± 12)% cars. The above differences probably reflect higher effectiveness in frontal (or rollover) crashes than in side impacts.