Comparison of frontal crash compatibility metrics between battery-electric and internal-combustion-engine passenger vehicles.

OBJECTIVE: The objective of this study was to determine if there are any emerging issues related to battery-electric vehicles' (BEVs') geometry, force distribution, and extra weight that may make them more aggressive partners in front-to-front crashes through comparisons of stiffness metrics derived from crash tests. METHODS: We examined load cell wall data from the National Highway Traffic Safety Administration's (NHTSA's) New Car Assessment Program full-width frontal crash test at 56 km/h. Fourteen BEVs, ranging in class from small cars to large SUVs, were compared with 92 internal-combustion-engine (ICE) vehicles, ranging in class from small cars to midsize pickups. We selected vehicles based on the test results available in the NHTSA Vehicle Crash Test Database, and there were no tests of battery-electric (BE) pickups. Data included load-cell-wall force-time histories and longitudinal vehicle acceleration from the body structure. We constructed force-displacement diagrams and calculated static, dynamic, energy-equivalent, and initial front-end-stiffness metrics from load cell wall forces, vehicle acceleration, and static front-end crush measurements for each vehicle. Linear regression models were applied to the metrics for comparison between powertrains. RESULTS: BE cars and BE SUVs weighed more than their ICE counterparts, on average 369 kg and 286 kg more, respectively. Initial (200 mm and 400 mm), energy-equivalent and dynamic front-end-stiffness metrics, average height of force, and individual maximum forces, when compared with vehicle shadow, were not statistically different between powertrains. Static stiffness (p = 0.04) and initial stiffness (300 mm; p = 0.05) decreased for BEVs with greater shadow and increased with greater shadow for ICE vehicles. When controlling for vehicle shadow, dynamic crush was greater (p = 0.01), the percentage of center force was lower (p < 0.001), and maximum peak force was higher (p = 0.01) for BEVs compared with ICE vehicles. For the Kia Niro BEV and ICE pair, the 329 kg heavier BEV had a 165 mm longer crush distance, which resulted in lower forces and stiffness metrics compared with the traditional ICE counterpart. CONCLUSION: Overall, this study indicates that current BEVs are not excessively aggressive in terms of stiffness metrics for frontal crash compatibility compared with ICE vehicles.

Light where it matters: IIHS headlight ratings are correlated with nighttime crash rates.

INTRODUCTION: Vehicle headlights are the primary means of providing visibility illumination for drivers at night, when crash rates are several times higher than during the day. Based on research indicating a wide range of headlight performance in the passenger vehicle fleet and the absence of a comprehensive and objective consumer evaluation program, the Insurance Institute for Highway Safety (IIHS) began testing and rating headlight systems in 2015. The purpose of this study was to examine the relationship between headlight visibility, as quantified by IIHS, and real-world crash occurrence. METHODS: Poisson regression was used to estimate the effects of the headlight rating and the underlying demerits on the rate of police-reported nighttime single-vehicle crashes per vehicle mile traveled. RESULTS: Results indicate that vehicles with better headlight visibility have lower nighttime crash rates after controlling for differences in daytime rates and other factors. A reduction of 10 visibility demerits, the equivalent of one overall rating band, was estimated to reduce the nighttime crash rate by 4.6% (95% CI: 2.1%-7.0%). While statistical significance was limited by small sample sizes, good-rated headlights were estimated to reduce crash rates by 12 to 29% relative to those with poor ratings for the different types of single-vehicle crashes studied. Among different components of the IIHS rating, the assessments of low and high beam curve visibility were associated with the greatest crash rate reductions. CONCLUSIONS: This study demonstrates that the IIHS evaluation program encourages headlight designs that reduce the risk of nighttime single-vehicle crashes. PRACTICAL APPLICATIONS: Headlight systems have a meaningful effect on nighttime crash rates. Drivers can reduce their crash risk by selecting a vehicle with one of the best designs.

Injury risks and crashworthiness benefits for females and males: Which differences are physiological?

OBJECTIVE: Previous research has found elevated injury risk for females relative to males in passenger vehicle crashes but has not accounted for ways the crashes themselves differ between these populations. Vehicle curb weight, ride height, safety rating, airbag deployment, and crash configuration all influence injury outcome and often are not well-represented by delta-V alone. This study evaluated the effect of occupant sex on injury risk in front and side crashes while limiting or controlling for non-physiological crash differences. Additionally, the effects of crashworthiness improvements are compared for females and males. METHODS: NASS-CDS cases from 1998-2015 calendar years involving a belted driver in a front crash or a struck-side driver or right front passenger in a side crash were analyzed. Case vehicle model years were 1989-2016. Logistic regression was used to estimate the risk of MAIS ≥ 2 and MAIS ≥ 3 injury outcomes for females relative to males as well as the change in risk due to improved crashworthiness. Sex-based differences in occupant age, mass, and stature; crash test rating; delta-V; crash configuration; and vehicle-to-vehicle compatibility were considered either through case selection or the inclusion of additional regression covariates. RESULTS: Before controlling for crash and vehicle differences, female drivers in front crashes had higher estimated overall and body-region-specific risks of MAIS ≥ 2 and MAIS ≥ 3 injury, as consistent with previous findings. After accounting for such differences, all ratios of injury odds for females relative to males were reduced. Females remained at higher risk of MAIS ≥ 2 injury (OR, 2.23; 95% CI, 1.42-3.51), especially extremity injury, but had similar odds for MAIS ≥ 3 non-extremity injury (OR, 0.98; 95% CI, 0.56-1.7). While controlling for crash differences in side impacts, none of the estimated injury risk differences by sex were significant at the p ≤ 0.05 level. Estimated benefits of improved crashworthiness were similar or greater for females than for males for most injury outcomes. CONCLUSIONS: Female-specific crashworthiness improvements may be required to provide additional protection against AIS 2 extremity injury. Much of the remaining discrepancy in sex-based injury risk can be attributed differences between vehicles and crashes, not to physiological differences. Addressing these differences will require other types of countermeasures.

High beam headlamp use rates: Effects of rurality, proximity of other traffic, and roadway curvature.

OBJECTIVE: The few observational studies of the prevalence of high beam use indicate the rate of high beam use is about 25% when vehicles are isolated from other vehicles on unlit roads. Recent studies were limited to 2-lane rural roads and used measurement methods that likely overestimated use. The current study examined factors associated with the rate of high beam use of isolated vehicles on a variety of roadways in the Ann Arbor, Michigan area. METHODS: Twenty observation sites were categorized as urban, rural, or on a rural/urban boundary and selected to estimate the effects of street lighting, road curvature, and direction of travel relative to the city on high beam use. Sites were selected in pairs so that a majority of traffic passing one site also passed through the other. Measurement of high beams relied on video data recorded for 2 nights at each site, and the video data also were used to derive a precise measure of the proximity of other traffic. Nearly 3,200 isolated vehicles (10 s or longer from other vehicles) were observed, representing 1,500-plus vehicle pairs. RESULTS: Across the sample, 18% of the vehicles used high beams. Seventy-three percent of the 1,500-plus vehicle pairs used low beams at each paired site, whereas 9% used high beams at both sites. Vehicles at rural sites and sites at the boundaries of Ann Arbor were more likely to use high beams than vehicles at urban sites, but use in rural areas compared with rural/urban boundary areas did not vary significantly. Rates at all sites were much lower than expected, ranging from 0.9 to 52.9%. High beam use generally increased with greater time between subject vehicles and leading vehicles and vehicles in the opposing lane. There were mixed findings associated with street lighting, road curvature, and direction of travel relative to the city. CONCLUSION: Maximizing visibility available to drivers from headlights includes addressing the substantial underuse of high beam headlamps. Advanced technologies such as high beam assist, which switches automatically between high and low beam headlamps depending on the presence of other traffic, can help to address this problem.

Drivers' detection of roadside targets when driving vehicles with three headlight systems during high beam activation.

A previous open-road experiment indicated that curve-adaptive HID headlights driven with low beams improved drivers' detection of low conspicuity targets compared with fixed halogen and fixed HID low beam systems. The current study used the same test environment and targets to assess whether drivers' detection of targets was affected by the same three headlight systems when using high beams. Twenty drivers search and responded for 60 8×12inch targets of high or low reflectance that were distributed evenly across straight and curved road sections as they drove at 30 mph on an unlit two-lane rural road. The results indicate that target detection performance was generally similar across the three systems. However, one interaction indicated that drivers saw low reflectance targets on straight road sections from further away when driving with the fixed halogen high beam condition compared with curve-adaptive HID high beam headlights and also indicated a possible benefit for the curve-adaptive HID high beams for high reflectance targets placed on the inside of curves. The results of this study conflict with the previous study of low beams, which showed a consistent benefit for the curve-adaptive HID low beams for targets placed on curves compared with fixed HID and fixed halogen low beam conditions. However, a comparison of mean detection distances from the two studies indicated uniformly longer mean target detection distances for participants driving with high beams and implicates the potential visibility benefits for systems that optimize proper high beam use.

Test track evaluation of headlight glare associated with adaptive curve HID, fixed HID, and fixed halogen low beam headlights.

Adaptive curve headlights swivel with steering input and are linked to reduced insurance claims and improved visual performance. This study assessed glare experienced from adaptive curve high-intensity discharge (HID), fixed (non-swiveling) HID and fixed halogen headlights - all tested in low beam mode. Twenty participants rated glare from vehicles' headlights using the DeBoer visual discomfort scale as a test driver drove towards them from five approaches on a test track. Participants rated the fixed halogen condition as less glaring than the adaptive curve and fixed HID conditions. There was no significant difference in ratings between the HID low-beam conditions. Collapsing across roadway approaches, the mean subjective ratings for the fixed halogen, adaptive curve HID and fixed HID low-beam conditions indicated 'satisfactory' levels of glare. Differences between subjective ratings were supported by illuminance data. Differences among the three low-beam systems appear minor, relative to their differences from a benchmark high-beam condition. Practitioner Summary: Insurance data indicates reduced claims associated with adaptive curve lighting. The current effort was to study how such lighting affects discomfort glare of oncoming drivers relative to conventional headlights. Participants rated halogen headlights as less glaring than fixed and adaptive curve HID low beams. Differences among systems were small and associated with acceptable levels of discomfort glare.

Occurrence of serious injury in real-world side impacts of vehicles with good side-impact protection ratings.

OBJECTIVE: The Insurance Institute for Highway Safety (IIHS) introduced its side impact consumer information test program in 2003. Since that time, side airbags and structural improvements have been implemented across the fleet and the proportion of good ratings has increased to 93% of 2012-2014 model year vehicles. Research has shown that drivers of good-rated vehicles are 70% less likely to die in a left-side crash than drivers of poor-rated vehicles. Despite these improvements, side impact fatalities accounted for about one quarter of passenger vehicle occupant fatalities in 2012. This study is a detailed analysis of real-world cases with serious injury resulting from side crashes of vehicles with good ratings in the IIHS side impact test. METHODS: NASS-CDS and Crash Injury Research and Engineering Network (CIREN) were queried for occupants of good-rated vehicles who sustained an Abbreviated Injury Scale (AIS) ≥ 3 injury in a side-impact crash. The resulting 110 cases were categorized by impact configuration and other factors that contributed to injury. Patterns of impact configuration, restraint performance, and occupant injury were identified and discussed in the context of potential upgrades to the current IIHS side impact test. RESULTS: Three quarters of the injured occupants were involved in near-side impacts. For these occupants, the most common factors contributing to injury were crash severities greater than the IIHS test, inadequate side-airbag performance, and lack of side-airbag coverage for the injured body region. In the cases where an airbag was present but did not prevent the injury, occupants were often exposed to loading centered farther forward on the vehicle than in the IIHS test. Around 40% of the far-side occupants were injured from contact with the struck-side interior structure, and almost all of these cases were more severe than the IIHS test. The remaining far-side occupants were mostly elderly and sustained injury from the center console, instrument panel, or seat belt. In addition, many far-side occupants were likely out of position due to events preceding the side impact and/or being unbelted. CONCLUSION: Individual changes to the IIHS side impact test have the potential to reduce the number of serious injuries in real-world crashes. These include impacting the vehicle farther forward (relevant to 28% of all cases studied), greater test severity (17%), the inclusion of far-side occupants (9%), and more restrictive injury criteria (9%). Combinations of these changes could be more effective.

Real-world injury patterns associated with Hybrid III sternal deflections in frontal crash tests.

OBJECTIVE: This study investigated the relationship between the peak sternal deflection measurements recorded by the Hybrid III 50th percentile male anthropometric test device (ATD) in frontal crash tests and injury and fatality outcomes for drivers in field crashes. METHODS: ATD sternal deflection data were obtained from the Insurance Institute for Highway Safety's 64 km/h, 40 percent overlap crashworthiness evaluation tests for vehicles with seat belt crash tensioners, load limiters, and good-rated structure. The National Automotive Sampling System Crashworthiness Data System (NASS-CDS) was queried for frontal crashes of these vehicles in which the driver was restrained by a seat belt and air bag. Injury probability curves were calculated by frontal crash type using the injuries coded in NASS-CDS and peak ATD sternal deflection data. Fatality Analysis Reporting System (FARS) front-to-front crashes with exactly one driver death were also studied to determine whether the difference in measured sternal deflections for the 2 vehicles was related to the odds of fatality. RESULTS: For center impacts, moderate overlaps, and large overlaps in NASS-CDS, the probability of the driver sustaining an Abbreviated Injury Scale (AIS) score ≥ 3 thoracic injury, or any nonextremity AIS ≥ 3 injury, increased with increasing ATD sternal deflection measured in crash tests. For small overlaps, however, these probabilities decreased with increasing deflection. For FARS crashes, the fatally injured driver more often was in the vehicle with the lower measured deflection in crash tests (55 vs. 45%). After controlling for other factors, a 5-mm difference in measured sternal deflections between the 2 vehicles was associated with a fatality odds ratio of 0.762 for the driver in the vehicle with the greater deflection (95% confidence interval = 0.373, 1.449). CONCLUSIONS: Restraint systems that reduce peak Hybrid III sternal deflection in a moderate overlap crash test are beneficial in real-world crashes with similar or greater overlap but likely have a disbenefit in crashes with small overlap. This may occur because belt-force limiters employed to control deflections allow excursion that could produce contact with interior vehicle components in small overlaps, given the more oblique occupant motion and potential inboard movement of the air bag. Although based on a limited number of cases, this interpretation is supported by differences in skeletal fracture locations among drivers in crashes with different overlaps. Current restraint systems could be improved by designs that reduce sternal deflection in moderate and large overlap crashes without increasing occupant excursion in small overlap crashes.

Potential benefits of underride guards in large truck side crashes.

OBJECTIVE: To evaluate the maximum potential for side underride guards (SUGs) to reduce passenger vehicle occupant fatalities and injuries in crashes with large trucks in the United States. METHODS: Examination of the Large Truck Crash Causation Study (LTCCS) identified 206 crash events involving a passenger vehicle impact with the side of a large truck. Each case was evaluated to determine whether the most severe injury sustained by a passenger vehicle occupant was a result of the impact with the side of the truck and whether an SUG could have reduced the injury severity. Data from the 2006-2008 Fatality Analysis Reporting System (FARS) and Trucks Involved in Fatal Accidents (TIFA) survey were used to compare the types of trucks involved in all fatal side impacts with passenger vehicles with the truck types in the LTCCS cases that were studied. FARS and TIFA data also were used to estimate the total annual number of passenger vehicle occupants killed in truck side impacts. RESULTS: In 143 of the 206 cases, the truck side impact produced the most severe injury sustained by a passenger vehicle occupant. In the other cases, no passenger vehicle occupant was injured or the most severe injury was due to an event preceding or following the truck side impact. Forty-nine of these occupants sustained injuries coded as level 3 or higher on the abbreviated injury scale (AIS) or were killed. SUGs could have reduced injury severity in 76 of the 143 cases, including 38 of the 49 cases with an AIS ≥ 3 coded injury or fatality. Semi-trailers were the most common type of impacted truck unit, both overall and when considering only cases where an SUG could have mitigated injury severity. Crashes where the front of the passenger vehicle struck the side of the semi-trailer perpendicularly or obliquely from the oncoming direction were less common overall than side-to-side and oblique/same direction crashes but more often produced an AIS ≥ 3 injury or fatality. The distribution of truck types in the LTCCS sample was similar to that in the FARS and TIFA data. Overall, around 1600 passenger vehicle occupants were killed in 2-vehicle truck side impact crashes during 2006-2008, or 22 percent of all passenger vehicle occupants who died in 2-vehicle crashes with large trucks. CONCLUSIONS: Structural incompatibility was a common factor in LTCCS crashes between passenger vehicles and the sides of large trucks. SUGs could have reduced injury risk in around three fourths of the crashes that produced an AIS ≥ 3 injury or fatality. Most of these crashes involved semi-trailers. However, the necessary strength and location of these SUGs present technical challenges that need to be addressed.

Evaluation of US rear underride guard regulation for large trucks using real-world crashes.

Current requirements for rear underride guards on large trucks are set by the National Highway Traffic Safety Administration in Federal Motor Vehicle Safety Standards (FMVSS) 223 and 224. The standards have been in place since 1998, but their adequacy has not been evaluated apart from two series of controlled crash tests. The current study used detailed reviews of real-world crashes from the Large Truck Crash Causation Study to assess the ability of guards that comply with certain aspects of the regulation to mitigate passenger vehicle underride. It also evaluated the dangers posed by underride of large trucks that are exempt from guard requirements. For the 115 cases meeting the inclusion criteria, coded data, case narratives, photographs, and measurements were used to examine the interaction between study vehicles. The presence and type of underride guard was determined, and its performance in mitigating underride was categorized. Overall, almost one-half of the passenger vehicles had underride damage classified as severe or catastrophic. These vehicles accounted for 23 of the 28 in which occupants were killed. For the cases involving trailers with underride guards compliant with one or both FMVSS, guard deformation or complete failure was frequent and most commonly due to weak attachments, buckling of the trailer chassis, or bending of the lateral end of the guard under narrow overlap loading. Most of the truck units studied qualified for at least one of the FMVSS exemptions. The two largest groups were trailers with small wheel setbacks and single-unit straight trucks. Dump trucks represented a particularly hazardous category of straight truck. The current study suggests several weaknesses in the rear underride guard regulation. The standard allows too much ground clearance, the quasi-static test conditions allow guard designs that fail in narrow overlap crashes, and certifying guards independent of trailers leads to systems with inadequate attachment and chassis strength. Additionally, the regulation should be expanded to cover a higher percentage of the large truck fleet.

Roof strength and injury risk in rollover crashes of passenger cars.

OBJECTIVE: A 2009 study by the Insurance Institute for Highway Safety found that midsize SUVs with stronger roofs, as measured in quasi-static tests, had lower risk of ejection and lower risk of injury for nonejected drivers. The objective of the present study was to determine whether a similar association exists for other vehicle groups. METHODS: Twelve small passenger cars were evaluated according to Federal Motor Vehicle Safety Standard 216 test conditions. Crash databases in 14 states provided more than 20,000 single-vehicle rollover crashes involving these vehicles. Logistic regression analyses were used to evaluate the effect of roof strength on the rate of driver injury while assessing and controlling for the effects of driver age, vehicle stability, state, and other factors where necessary. RESULTS: Small cars with stronger roofs had lower overall rates of serious injury, lower rates of ejection, and lower rates of injury for nonejected drivers. Although the effect on ejection was somewhat smaller for cars than for SUVs, the overall pattern of injury results was consistent. For roof strength-to-weight ratio measured within 5 in. (SWR(5)), a one-unit increase (e.g., from 2.0 to 3.0) was associated with a 22 percent reduction in risk of incapacitating or fatal driver injury in single-vehicle rollovers. This compares with a 24 percent reduction estimated for a similar change in roof strength among midsize SUVs. CONCLUSIONS: The association between vehicle roof strength and occupant injury risk in rollover crashes appears robust across different vehicle groups and across roof SWR(5) values, varying from just more than 1.5 to just less than 4.0. If roofs were to increase in strength by one SWR(5), a 20-25 percent reduction in risk of serious injury in rollovers would be expected. Still, even if all vehicle roofs were as strong as the strongest roof measured, many rollover injuries still would occur, indicating the need for additional research and countermeasures.

Roof strength and injury risk in rollover crashes.

OBJECTIVE: Previous studies have reported that roof strength as measured in FMVSS 216 is unrelated to occupant injury risk in actual rollovers. However, those studies did not control for important confounding factors. The present study reevaluated roof strength and injury risk using a single class of vehicles with similar driver and vehicle usage characteristics in the expectation that some potential confounders will be controlled by this focused analysis. Alternative roof strength measures also were examined in case strength-to-weight ratio (SWR) at 5 inches, the measure in FMVSS 216, is not the best measure. METHODS: Eleven midsize SUV roof designs were crushed according to FMVSS 216 protocol. Force was measured continuously, and the maximum force and the amount of energy used to achieve crush of 2, 5, and 10 inches were recorded; these six measures of roof strength were evaluated both directly and after normalization for vehicle weight. After controlling for other potentially confounding variables, logistic regression models estimated the effect of each of the twelve roof strength measures on risk of fatal or incapacitating injuries to drivers in single-vehicle rollover crashes. Crash data were obtained from fourteen states. RESULTS: All roof strength measures correlated inversely, and similarly, with risk of fatal/incapacitating injury in single-vehicle rollovers. Across all states, 12 percent of drivers sustained fatal/incapacitating injuries, but individual state rates varied from 6 to 24 percent. Among available variables, only state substantially affected the estimated effect of roof strength; it was kept in the final models with roof strength, driver age, and static stability factor (SSF). Driver age was retained because it had a significant effect on injury outcome and SSF was retained for theoretical reasons. This model estimated that a one-unit increase in strength-to-weight ratio (SWR) within 5 inches of crush was associated with 24 percent lower risk of fatal/incapacitating injury (95% CI: 15-33). Ejection was lower by 41 percent (95% CI: 30-51), and injury risk among nonejected occupants was lower by 16 percent (95% CI: 3-29). CONCLUSIONS: The FMVSS 216 measure of roof strength related strongly to occupant protection in real-world rollover crashes in this study, which restricted analysis to vehicles with reasonably homogeneous driver and usage characteristics and accounted for state variation in injury rates. Further research should determine whether these results generalize to other vehicle types with different drivers and rollover risk. Research should also focus on factors other than roof strength, because even large increases in roof strength would leave many rollover crash deaths unaffected.