Estimated benefit of automated emergency braking systems for vehicle–pedestrian crashes in the United States

Abstract

Objective: The objective of this research study is to estimate the benefit to pedestrians if all U.S. cars, light trucks, and vans were equipped with an automated braking system that had pedestrian detection capabilities.

Methods: A theoretical automatic emergency braking (AEB) model was applied to real-world vehicle–pedestrian collisions from the Pedestrian Crash Data Study (PCDS). A series of potential AEB systems were modeled across the spectrum of expected system designs. Both road surface conditions and pedestrian visibility were accounted for in the model. The impact speeds of a vehicle without AEB were compared to the estimated impact speeds of vehicles with a modeled pedestrian detecting AEB system. These impacts speeds were used in conjunction with an injury and fatality model to determine risk of Maximum Abbreviated Injury Scale of 3 or higher (MAIS 3+) injury and fatality.

Results: AEB systems with pedestrian detection capability, across the spectrum of expected design parameters, reduced fatality risk when compared to human drivers. The most beneficial system (time-to-collision [TTC]?=?1.5?s, latency = 0?s) decreased fatality risk in the target population between 84 and 87% and injury risk (MAIS score 3+) between 83 and 87%.

Conclusions: Though not all crashes could be avoided, AEB significantly mitigated risk to pedestrians. The longer the TTC of braking and the shorter the latency value, the higher benefits showed by the AEB system. All AEB models used in this study were estimated to reduce fatalities and injuries and were more effective when combined with driver braking.     

Impact of improving vehicle front design on the burden of pedestrian injuries in Germany,the United States,and India

Objective: European car design regulations and New Car Assessment Program (NCAP) ratings have led to reductions in pedestrian injuries. The aim of this study was to evaluate the impact of improving vehicle front design on mortality and morbidity due to pedestrian injuries in a European country (Germany) and 2 countries (the United States and India) that do not have pedestrian-focused NCAP testing or design regulations.

Methods: We used data from the International Road Traffic and Accident Database and the Global Burden of Disease project to estimate baseline pedestrian deaths and nonfatal injuries in each country in 2013. The effect of improved passenger car star ratings on probability of pedestrian injury was based on recent evaluations of pedestrian crash data from Germany. The effect of improved heavy motor vehicle (HMV) front end design on pedestrian injuries was based on estimates reported by simulation studies. We used burden of disease methods to estimate population health loss by combining the burden of morbidity and mortality in disability-adjusted life years (DALYs) lost.

Results: Extrapolating from evaluations in Germany suggests that improving front end design of cars can potentially reduce the burden of pedestrian injuries due to cars by up to 24% in the United States and 41% in India. In Germany, where cars comply with the United Nations regulation on pedestrian safety, additional improvements would have led to a 1% reduction. Similarly, improved HMV design would reduce DALYs lost by pedestrian victims hit by HMVs by 20% in each country. Overall, improved vehicle design would reduce DALYs lost to road traffic injuries (RTIs) by 0.8% in Germany, 4.1% in the United States, and 6.7% in India.

Conclusions: Recent evaluations show a strong correlation between Euro NCAP pedestrian scores and real-life pedestrian injuries, suggesting that improved car front end design in Europe has led to substantial reductions in pedestrian injuries. Although the United States has fewer pedestrian crashes, it would nevertheless benefit substantially by adopting similar regulations and instituting pedestrian NCAP testing. The maximum benefit would be realized in low- and middle-income countries like India that have a high proportion of pedestrian crashes. Though crash avoidance technologies are being developed to protect pedestrians, supplemental protection through design regulations may significantly improve injury countermeasures for vulnerable road users.     

Association Between NCAP Ratings and Real-World Rear Seat Occupant Risk of Injury

Objective: Several studies have evaluated the correlation between U.S. or Euro New Car Assessment Program (NCAP) ratings and injury risk to front seat occupants, in particular driver injuries. Conversely, little is known about whether NCAP 5-star ratings predict real-world risk of injury to restrained rear seat occupants. The NHTSA has identified rear seat occupant protection as a specific area under consideration for improvements to its NCAP. In order to inform NHTSA's efforts, we examined how NCAP's current 5-star rating system predicts risk of moderate or greater injury among restrained rear seat occupants in real-world crashes.

Methods: We identified crash-involved vehicles, model year 2004–2013, in NASS-CDS (2003–2012) with known make and model and nonmissing occupant information. We manually matched these vehicles to their NCAP star ratings using data on make, model, model year, body type, and other identifying information. The resultant linked NASS-CDS and NCAP database was analyzed to examine associations between vehicle ratings and rear seat occupant injury risk; risk to front seat occupants was also estimated for comparison. Data were limited to restrained occupants and occupant injuries were defined as any injury with a maximum Abbreviated Injury Scale (AIS) score of 2 or greater.

Results: We linked 95% of vehicles in NASS-CDS to a specific vehicle in NCAP. The 18,218 vehicles represented an estimated 6 million vehicles with over 9 million occupants. Rear seat passengers accounted for 12.4% of restrained occupants. The risk of injury in all crashes for restrained rear seat occupants was lower in vehicles with a 5-star driver rating in frontal impact tests (1.4%) than with 4 or fewer stars (2.6%, P =.015); results were similar for the frontal impact passenger rating (1.3% vs. 2.4%, P =.024). Conversely, side impact driver and passenger crash tests were not associated with rear seat occupant injury risk (driver test: 1.7% for 5-star vs. 1.8% for 1–4 stars; passenger test: 1.6% for 5 stars vs 1.8% for 1–4 stars).

Conclusions: Current frontal impact test procedures provide some degree of discrimination in real-world rear seat injury risk among vehicles with 5 compared to fewer than 5 stars. However, there is no evidence that vehicles with a 5-star side impact passenger rating, which is the only crash test procedure to include an anthropomorphic test dummy (ATD) in the rear, demonstrate lower risks of injury in the rear than vehicles with fewer than 5 stars. These results support prioritizing modifications to the NCAP program that specifically evaluate rear seat injury risk to restrained occupants of all ages.     

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.     

Multi-agent traffic simulations to estimate the impact of automated technologies on safety

Abstract

Objective: The objective of this article was to develop a multi-agent traffic simulation methodology to estimate the potential road safety improvements of automated vehicle technologies.

Methods: We developed a computer program that merges road infrastructure data with a large number of vehicles, drivers, and pedestrians. Human errors are induced by modeling inattention, aimless driving, insufficient safety confirmation, misjudgment, and inadequate operation. The program was applied to simulate traffic in a prescribed area in Tsukuba city. First, a 100% manual driving scenario was set to simulate traffic for a total preset vehicle travel distance. The crashes from this simulation were compared with real-world crash data from the prescribed area from 2012 to 2017. Thereafter, 4 additional scenarios of increasing levels of automation penetration (including combinations of automated emergency braking [AEB], lane departure warning [LDW], and SAE Level 4 functions) were implemented to estimate their impact on safety.

Results: Under manual driving, the system simulated a total of 859 crashes including single-car lane departure, car-to-car, and car-to-pedestrian crashes. These crashes tended to occur in locations similar to real-world crashes. The number of crashes predicted decreased to 156 cases with increasing level of automation. All of the technologies considered contributed to the decrease in crashes. Crash reductions attributable to AEB and LDW in the simulations were comparable to those reported in recent field studies. For the highest levels of automation, no assessment data were available and hence the results should be carefully treated. Further, in modeling automated functions, potentially negative aspects such as sensing failure or human overreliance were not incorporated.

Conclusions: We developed a multi-agent traffic simulation methodology to estimate the effect of different automated vehicle technologies on safety. The crash locations resulting from simulations of manual driving within a limited area in Japan were preliminary assessed by comparison with real-world crash data collected in the same area. Increasing penetration levels of AEB and LDW led to a large reduction in both the frequency and severity of rear-end crashes, followed by car-to-car head-on crashes and single-vehicle lane departure crashes. Preliminary estimations of the potential safety improvements that may be achieved with highly automated driving technologies were also obtained.     

Analyzing pedestrian crash injury severity under different weather conditions

Objective: Pedestrians are the most vulnerable road users due to the lack of mass, speed, and protection compared to other types of road users. Adverse weather conditions may reduce road friction and visibility and thus increase crash risk. There is limited evidence and considerable discrepancy with regard to impacts of weather conditions on injury severity in the literature. This article investigated factors affecting pedestrian injury severity level under different weather conditions based on a publicly available accident database in Great Britain.

Method: Accident data from Great Britain that are publicly available through the STATS19 database were analyzed. Factors associated with pedestrian, driver, and environment were investigated using a novel approach that combines a classification and regression tree with random forest approach.

Results: Significant severity predictors under fine weather conditions from the models included speed limits, pedestrian age, light conditions, and vehicle maneuver. Under adverse weather conditions, the significant predictors were pedestrian age, vehicle maneuver, and speed limit.

Conclusions: Elderly pedestrians are associated with higher pedestrian injury severities. Higher speed limits increase pedestrian injury severity. Based on the research findings, recommendations are provided to improve pedestrian safety.     

Estimating the value of life and injury for pedestrians using a stated preference framework

IntroductionThe incidence of pedestrian death over the period 2010 to 2014 per 1000,000 in North Cyprus is about 2.5 times that of the EU, with 10.5 times more pedestrian road injuries than deaths. With the prospect of North Cyprus entering the EU, many investments need to be undertaken to improve road safety in order to reach EU benchmarks.MethodWe conducted a stated choice experiment to identify the preferences and tradeoffs of pedestrians in North Cyprus for improved walking times, pedestrian costs, and safety. The choice of route was examined using mixed logit models to obtain the marginal utilities associated with each attribute of the routes that consumers chose. These were used to estimate the individuals' willingness to pay (WTP) to save walking time and to avoid pedestrian fatalities and injuries. We then used the results to obtain community-wide estimates of the value of a statistical life (VSL) saved, the value of an injury (VI) prevented, and the value per hour of walking time saved.ResultsThe estimate of the VSL was €699,434 and the estimate of VI was €20,077. These values are consistent, after adjusting for differences in incomes, with the median results of similar studies done for EU countries. The estimated value of time to pedestrians is €7.20 per person hour.ConclusionsThe ratio of deaths to injuries is much higher for pedestrians than for road accidents, and this is completely consistent with the higher estimated WTP to avoid a pedestrian accident than to avoid a car accident. The value of time of €7.20 is quite high relative to the wages earned.Practical applicationsFindings provide a set of information on the VRR for fatalities and injuries and the value of pedestrian time that is critical for conducing ex ante appraisals of investments to improve pedestrian safety.     

Personal injury recovery cost of pedestrian–vehicle collisions in New South Wales,Australia

Background: There is a need for routine estimates of injury recovery costs from pedestrian collisions using hospital separation records for economic evaluations.

Objective: To estimate the cost of injury recovery following pedestrian–vehicle collisions using the personal injury recover cost (PIRC) equation using key demographic and injury characteristics.

Method: An estimation of the costs of on-road pedestrian–vehicle collisions involving individuals who were injured and hospitalized in New South Wales (NSW), Australia, from 2002 to 2011 using the PIRC equation. The PIRC estimates individual injury recovery costs and does not include costs associated with property damage, vehicle repair, or rescue services. Individual recovery costs associated with severe traumatic brain injury (TBI) were estimated. The injured individual's mean, median, and total injury recovery costs are described for key demographic, injury, and crash characteristics.

Results: There were 9,781 pedestrians who were injured, costing an estimated total of $2.4 billion in personal injury recovery costs, an annual cost of $243 million. Males had a total injury recovery cost 1.7 times higher than females. The median injury recovery cost decreased with increasing age. TBI ($248,491) and spinal cord and vertebral column injuries ($264,103) had the highest median injury recovery costs for the body region of the most severe injury. TBI accounted for 22.6% of the total injury recovery costs for the most severe injury sustained. Just over one third of pedestrians sustained 4 or more injuries, with a median cost of $243,992, which was 1.6 times higher than the cost for a pedestrian who sustained a single injury ($153,682).

Conclusions: Personal injury recovery costs following pedestrian–vehicle collisions where a pedestrian is injured are substantial in NSW. The PIRC equation enables the economic cost burden of road traffic injury to be calculated using hospital separation data. The PIRC enables comprehensive personal injury recovery costs to be estimated and would aid in economic evaluations of preventive strategies in road safety.     

Evaluation of the effectiveness of traffic calming measures on vehicle speeds and pedestrian injury severity in Ghana

Objectives: Each year, pedestrian injuries constitute over 40% of all road casualty deaths and up to 60% of all urban road casualty deaths in Ghana. This is as a result of the overwhelming dependence on walking as a mode of transport in an environment where there are high vehicular speeds and inadequate pedestrian facilities. The objectives of this research were to establish the (1) impact of traffic calming measures on vehicle speeds and (2) association between traffic calming measures and pedestrian injury severity in built-up areas in Ghana.

Method: Vehicle speeds were unobtrusively measured in 38 selected settlements, including 19 with traffic calming schemes and 19 without. The study design used in this research was a matched case–control. A regression analysis compared case and control casualties using a conditional logistic regression.

Results: Generally, the mean vehicle speeds and the proportion of vehicles exceeding the 50?km/h speed limit were significantly lower in settlements that have traffic calming measures compared to towns without any traffic calming measures. Additionally, the proportion of motorists who exceeded the speed limit was 30% or less in settlements that have traffic calming devices and the proportion who exceeded the speed limit was 60% or more in towns without any traffic calming measures. The odds of pedestrian fatality was significantly higher in settlements that have no traffic calming devices compared to those that have (odds ratio [OR]?=?1.98; 95% confidence interval, 1.09–4.43). The protective effects of a traffic calming scheme that has a speed table was notably higher than those where there were no speed tables.

Conclusion: It was clearly evident that traffic calming devices reduce vehicular speeds and, thus, the incidence and severity of pedestrian injuries in built-up areas in Ghana. However, the fact that they are deployed on arterial roads is increasingly becoming a road safety concern. Given the emerging safety challenges associated with speed calming measures, we recommend that their use be restricted to residential streets but not on arterial roads. Long-term solutions for improving pedestrian safety proposed herein include bypassing settlements along the highways to reduce pedestrians’ exposure to traffic collisions and adopting a modern way of enforcement such as evidence-based laser monitoring in conjunction with a punishment regime that utilizes the demerit points system.     

Can new passenger cars reduce pedestrian lower extremity injury? A review of geometrical changes of front-end design before and after regulatory efforts

Objective: Pedestrian lower extremity represents the most frequently injured body region in car-to-pedestrian accidents. The European Directive concerning pedestrian safety was established in 2003 for evaluating pedestrian protection performance of car models. However, design changes have not been quantified since then. The goal of this study was to investigate front-end profiles of representative passenger car models and the potential influence on pedestrian lower extremity injury risk.

Methods: The front-end styling of sedans and sport utility vehicles (SUV) released from 2008 to 2011 was characterized by the geometrical parameters related to pedestrian safety and compared to representative car models before 2003. The influence of geometrical design change on the resultant risk of injury to pedestrian lower extremity—that is, knee ligament rupture and long bone fracture—was estimated by a previously developed assessment tool assuming identical structural stiffness. Based on response surface generated from simulation results of a human body model (HBM), the tool provided kinematic and kinetic responses of pedestrian lower extremity resulted from a given car's front-end design.

Results: Newer passenger cars exhibited a “flatter” front-end design. The median value of the sedan models provided 87.5 mm less bottom depth, and the SUV models exhibited 94.7 mm less bottom depth. In the lateral impact configuration similar to that in the regulatory test methods, these geometrical changes tend to reduce the injury risk of human knee ligament rupture by 36.6 and 39.6% based on computational approximation. The geometrical changes did not significantly influence the long bone fracture risk.

Conclusions: The present study reviewed the geometrical changes in car front-ends along with regulatory concerns regarding pedestrian safety. A preliminary quantitative benefit of the lower extremity injury reduction was estimated based on these geometrical features. Further investigation is recommended on the structural changes and inclusion of more accident scenarios.     

Older Adults at Increased Risk as Pedestrians in Victoria,Australia: An Examination of Crash Characteristics and Injury Outcomes

Objectives: Engaging in active transport modes (especially walking) is a healthy and environmentally friendly alternative to driving and may be particularly beneficial for older adults. However, older adults are a vulnerable group: they are at higher risk of injury compared with younger adults, mainly due to frailty and may be at increased risk of collision due to the effects of age on sensory, cognitive, and motor abilities. Moreover, our population is aging, and there is a trend for the current cohort of older adults to maintain mobility later in life compared with previous cohorts. Though these trends have serious implications for transport policy and safety, little is known about the contributing factors and injury outcomes of pedestrian collision. Further, previous research generally considers the older population as a homogeneous group and rarely considers the increased risks associated with continued ageing.

Method: Collision characteristics and injury outcomes for 2 subgroups of older pedestrians (65–74 years and 75+ years) were examined by extracting data from the state police–reported crash dataset and hospital admission/emergency department presentation data over the 10-year period between 2003 and 2012. Variables identified for analysis included pedestrian characteristics (age, gender, activity, etc.), crash location and type, injury characteristics and severity, and duration of hospital stay. A spatial analysis of crash locations was also undertaken to identify collision clusters and the contribution of environmental features on collision and injury risk.

Results: Adults over 65 years were involved in 21% of all pedestrian collisions. A high fatality rate was found among older adults, particularly for those aged 75 years and older: this group had 3.2 deaths per 100,000 population, compared to a rate of 1.3 for 65- to 74-year-olds and 0.7 for adults below 65 years of age. Older pedestrian injuries were most likely to occur while crossing the carriageway; they were also more likely to be injured in parking lots, at driveway intersections, and on sidewalks compared to younger cohorts. Spatial analyses revealed older pedestrian crash clusters on arterial roads in urban shopping precincts. Significantly higher rates of hospital admissions were found for pedestrians over the age of 75 years and for abdominal, head, and neck injuries; conversely, older adults were underrepresented in emergency department presentations (mainly lower and upper extremity injuries), suggesting an increased severity associated with older pedestrian injuries. Average length of hospital stay also increased with increasing age.

Conclusion: This analysis revealed age differences in collision risk and injury outcomes among older adults and that aggregate analysis of older pedestrians can distort the significance of risk factors associated with older pedestrian injuries. These findings have implications that extend to the development of engineering, behavioral, and enforcement countermeasures to address the problems faced by the oldest pedestrians and reduce collision risk and improve injury outcomes.     

Brake reactions of distracted drivers to pedestrian Forward Collision Warning systems

Introduction: Forward Collision Warning (FCW) can be effective in directing driver attention towards a conflict and thereby aid in preventing or mitigating collisions. FCW systems aiming at pedestrian protection have been introduced onto the market, yet an assessment of their safety benefits depends on the accurate modeling of driver reactions when the system is activated. This study contributes by quantifying brake reaction time and brake behavior (deceleration levels and jerk) to compare the effectiveness of an audio-visual warning only, an added haptic brake pulse warning, and an added Head-Up Display in reducing the frequency of collisions with pedestrians. Further, this study provides a detailed data set suited for the design of assessment methods for car-to-pedestrian FCW systems. Method: Brake response characteristics were measured for heavily distracted drivers who were subjected to a single FCW event in a high-fidelity driving simulator. The drivers maintained a self-regulated speed of 30 km/h in an urban area, with gaze direction diverted from the forward roadway by a secondary task. Results: Collision rates and brake reaction times differed significantly across FCW settings. Brake pulse warnings resulted in the lowest number of collisions and the shortest brake reaction times (mean 0.8 s, SD 0.29 s). Brake jerk and deceleration were independent of warning type. Ninety percent of drivers exceeded a maximum deceleration of 3.6 m/s² and a jerk of 5.3 m/s³. Conclusions: Brake pulse warning was the most effective FCW interface for preventing collisions. In addition, this study presents the data required for driver modeling for car-to-pedestrian FCW similar to Euro NCAP's 2015 car-to-car FCW assessment. Practical applications: Vehicle manufacturers should consider the introduction of brake pulse warnings to their FCW systems. Euro NCAP could introduce an assessment that quantifies the safety benefits of pedestrian FCW systems and thereby aid the proliferation of effective systems.     

Effects of speed-control measures on the safety of unsignalized midblock street crossings in China

Objective: The primary objective of this study was to evaluate the effects of different speed-control measures on the safety of unsignalized midblock street crossings.

Methods: In China, it is quite difficult to obtain traffic crash and conflict data for pedestrians using such crossings, mainly due to the lack of traffic data management and organizational issues. In light of this, the proposed method did not rely on such data, but considered vehicle speed, which is a leading contributing factor of pedestrian safety at mid blocks. To evaluate the speed reduction effects at different locations, the research team utilized the following methods in this study: (1) testing speed differences—on the basis of the collected data, statistical analysis is conducted to test the speed differences between upstream and crosswalk, upstream and downstream, and downstream and crosswalk; and (2) mean distribution deviation—this value is calculated by taking the difference in cumulative speed distributions for the two different samples just mentioned. In order to better understand the variation of speed reduction effects at different distances from speed-control facilities, data were collected from six types of speed-control measures with a visual range of 60 m.

Results: The results showed that speed humps, transverse rumble strips, and speed bumps were effective in reducing vehicle speeds. Among them speed humps performed the best, with reductions of 21.1% and 20.0% from upstream location (25.01 km/h) and downstream location (24.66 km/h) to pedestrian crosswalk (19.73 km/h), respectively. By contrast, the speed reduction effects were minimal for stop and yield signs, flashing yellow lights, and crossings without treatment.

Conclusions: Consequently, in order to reduce vehicle speeds and improve pedestrian safety at mid blocks, several speed-control measures such as speed humps, speed bumps, and transverse rumble strips are recommended to be deployed in the vicinity of pedestrian crosswalks.     

A virtual test system representing the distribution of pedestrian impact configurations for future vehicle front-end optimization

Objectives: The purpose of this study is to define a computationally efficient virtual test system (VTS) to assess the aggressivity of vehicle front-end designs to pedestrians considering the distribution of pedestrian impact configurations for future vehicle front-end optimization. The VTS should represent real-world impact configurations in terms of the distribution of vehicle impact speeds, pedestrian walking speeds, pedestrian gait, and pedestrian height. The distribution of injuries as a function of body region, vehicle impact speed, and pedestrian size produced using this VTS should match the distribution of injuries observed in the accident data. The VTS should have the predictive ability to distinguish the aggressivity of different vehicle front-end designs to pedestrians.

Methods: The proposed VTS includes 2 parts: a simulation test sample (STS) and an injury weighting system (IWS). The STS was defined based on MADYMO multibody vehicle to pedestrian impact simulations accounting for the range of vehicle impact speeds, pedestrian heights, pedestrian gait, and walking speed to represent real world impact configurations using the Pedestrian Crash Data Study (PCDS) and anthropometric data. In total 1,300 impact configurations were accounted for in the STS. Three vehicle shapes were then tested using the STS. The IWS was developed to weight the predicted injuries in the STS using the estimated proportion of each impact configuration in the PCDS accident data. A weighted injury number (WIN) was defined as the resulting output of the VTS. The WIN is the weighted number of average Abbreviated Injury Scale (AIS) 2+ injuries recorded per impact simulation in the STS. Then the predictive capability of the VTS was evaluated by comparing the distributions of AIS 2+ injuries to different pedestrian body regions and heights, as well as vehicle types and impact speeds, with that from the PCDS database. Further, a parametric analysis was performed with the VTS to assess the sensitivity of the injury predictions to changes in vehicle shape (type) and stiffness to establish the potential for using the VTS for future vehicle front-end optimization.

Results: An STS of 1,300 multibody simulations and an IWS based on the distribution of impact speed, pedestrian height, gait stance, and walking speed is broadly capable of predicting the distribution of pedestrian injuries observed in the PCDS database when the same vehicle type distribution as the accident data is employed. The sensitivity study shows significant variations in the WIN when either vehicle type or stiffness is altered.

Conclusions: Injury predictions derived from the VTS give a good representation of the distribution of injuries observed in the PCDS and distinguishing ability on the aggressivity of vehicle front-end designs to pedestrians. The VTS can be considered as an effective approach for assessing pedestrian safety performance of vehicle front-end designs at the generalized level. However, the absolute injury number is substantially underpredicted by the VTS, and this needs further development.     

Integrated pedestrian countermeasures - Potential of head injury reduction combining passive and active countermeasures

A rapid development of both pedestrian passive and active safety, such as pedestrian bonnets/airbags and autonomous braking, is in progress. The aim of this study was to investigate the potential pedestrian head injury reduction from hypothetical passive and active countermeasures compared to an integrated system. The German In-Depth Accident Study (GIDAS) database was queried from 1999 to 2008 for severely (AIS3+) head injured pedestrians when struck by car or van fronts. This, resulted in 54 cases where information was sufficient. The passive countermeasure was designed to mitigate head injuries caused by the bonnet area, A-pillars, and the remaining windscreen area up to 2.1 m wrap around distance (WAD). The active countermeasure was an autonomous braking system, which was activated one second prior to impact if the pedestrian was visible to a forward-looking sensor. The integrated system was a direct combination of the passive and active countermeasures. Case by case the effect from each of the active, passive and integrated systems was estimated. For the integrated system, the influence of the active system on the passive system performance was explicitly modeled in each case. The integrated system resulted in 50% (95% confidence interval: 30-70%) greater effectiveness than the active countermeasure in reducing the number of pedestrians sustaining severe (AIS3+) head injuries, and 90% (95% CI: 50-150%) greater effectiveness than the passive countermeasure. Integrated systems of passive and active pedestrian countermeasures offer a considerably increased potential for head injury reduction compared to either of the two systems alone.     

Considering built environment and spatial correlation in modeling pedestrian injury severity

Objective: This study looks at mitigating and aggravating factors that are associated with the injury severity of pedestrians when they have crashes with another road user and overcomes existing limitations in the literature by focusing attention on the built environment and considering spatial correlation across crashes.

Method: Reports for 6,539 pedestrian crashes occurred in Denmark between 2006 and 2015 were merged with geographic information system resources containing detailed information about the built environment and exposure at the crash locations. A linearized spatial logit model estimated the probability of pedestrians sustaining a severe or fatal injury conditional on the occurrence of a crash with another road user.

Results: This study confirms previous findings about older pedestrians and intoxicated pedestrians being the most vulnerable road users and crashes with heavy vehicles and in roads with higher speed limits being related to the most severe outcomes. This study provides novel perspectives by showing positive spatial correlations of crashes with the same severity outcomes and emphasizing the role of the built environment in the proximity of the crash.

Conclusions: This study emphasizes the need for thinking about traffic calming measures, illumination solutions, road maintenance programs, and speed limit reductions. Moreover, this study emphasizes the role of the built environment, because shopping areas, residential areas, and walking traffic density are positively related to a reduction in pedestrian injury severity. Often, these areas have in common a larger pedestrian mass that is more likely to make other road users more aware and attentive, whereas the same does not seem to apply to areas with lower pedestrian density.     

Detection of the toughest: Pedestrian injury risk as a smooth function of age

Objective: Though it is common to refer to age-specific groups (e.g., children, adults, elderly), smooth trends conditional on age are mainly ignored in the literature. The present study examines the pedestrian injury risk in full-frontal pedestrian-to–passenger car accidents and incorporates age—in addition to collision speed and injury severity—as a plug-in parameter.

Methods: Recent work introduced a model for pedestrian injury risk functions using explicit formulae with easily interpretable model parameters. This model is expanded by pedestrian age as another model parameter. Using the German In-Depth Accident Study (GIDAS) to obtain age-specific risk proportions, the model parameters are fitted to the raw data and then smoothed by broken-line regression.

Results: The approach supplies explicit probabilities for pedestrian injury risk conditional on pedestrian age, collision speed, and injury severity under investigation. All results yield consistency to each other in the sense that risks for more severe injuries are less probable than those for less severe injuries. As a side product, the approach indicates specific ages at which the risk behavior fundamentally changes. These threshold values can be interpreted as the most robust ages for pedestrians.

Conclusions: The obtained age-wise risk functions can be aggregated and adapted to any population. The presented approach is formulated in such general terms that in can be directly used for other data sets or additional parameters; for example, the pedestrian's sex. Thus far, no other study using age as a plug-in parameter can be found.     

Characteristics of rear-end crashes involving passenger vehicles with automatic emergency braking

Abstract

Objectives: Automatic emergency braking (AEB) is a proven effective countermeasure for preventing front-to-rear crashes, but it has not yet fully lived up to its estimated potential. This study identified the types of rear-end crashes in which striking vehicles with AEB are overrepresented to determine whether the system is more effective in some situations than in others, so that additional opportunities for increasing AEB effectiveness might be explored.

Methods: Rear-end crash involvements were extracted from 23?U.S. states during 2009–2016 for striking passenger vehicles with and without AEB among models where the system was optional. Logistic regression was used to examine the odds that rear-end crashes with various characteristics involved a striking vehicle with AEB, controlling for driver and vehicle features.

Results: Striking vehicles were significantly more likely to have AEB in crashes where the striking vehicle was turning relative to when it was moving straight (odds ratio [OR]?=?2.35; 95% confidence interval [CI], 1.76, 3.13); when the struck vehicle was turning (OR = 1.66; 95% CI, 1.25, 2.21) or changing lanes (OR = 2.05; 95% CI, 1.13, 3.72) relative to when it was slowing or stopped; when the struck vehicle was not a passenger vehicle or was a special use vehicle relative to a car (OR = 1.61; 95% CI, 1.01, 2.55); on snowy or icy roads relative to dry roads (OR = 1.83; 95% CI, 1.16, 2.86); or on roads with speed limits of 70+ mph relative to those with 40 to 45?mph speed limits (OR = 1.49; 95% CI, 1.10, 2.03). Overall, 25.3% of crashes where the striking vehicle had AEB had at least one of these overrepresented characteristics, compared with 15.9% of strikes by vehicles without AEB.

Conclusions: The typical rear-end crash occurs when 2 passenger vehicles are proceeding in line, on a dry road, and at lower speeds. Because atypical crash circumstances are overrepresented among rear-end crashes by striking vehicles with AEB, it appears that the system is doing a better job of preventing the more typical crash scenario. Consumer information testing programs of AEB use a test configuration that models the typical rear-end crash type. Testing programs promoting good AEB performance in crash circumstances where vehicles with AEB are overrepresented could guide future development of AEB systems that perform well in these additional rear-end collision scenarios.