Modelling crash propensity of carshare members

Carshare systems are considered a promising solution for sustainable development of cities. To promote carsharing it is imperative to make them cost effective, which includes reduction in costs associated to crashes and insurance. To achieve this goal, it is important to characterize carshare users involved in crashes and understand factors that can explain at-fault and not-at fault drivers. This study utilizes data from GoGet carshare users in Sydney, Australia. Based on this study it was found that carshare users who utilize cars less frequently, own one or more cars, have less number of accidents in the past ten years, have chosen a higher insurance excess and have had a license for a longer period of time are less likely to be involved in a crash. However, if a crash occurs, carshare users not needing a car on the weekend, driving less than 1000 km in the last year, rarely using a car and having an Australian license increases the likelihood to be at-fault. Since the dataset contained information about all members as well as not-at-fault drivers, it provided a unique opportunity to explore some aspects of quasi-induced exposure. The results indicate systematic differences in the distribution between the not-at-fault drivers and the carshare members based on the kilometres driven last year, main mode of travel, car ownership status and how often the car is needed. Finally, based on this study it is recommended that creating an incentive structure based on training and experience (based on kilometres driven), possibly tagged to the insurance excess could improve safety, and reduce costs associated to crashes for carshare systems.     

Novel method for improving fatigue behaviour of laminated glass

Fatigue‐prone structures made of the laminated glass (LG) are yet not given the due consideration by the scientific community. In this work, a novel method that increases the fatigue life and improves the post breakage performance of the LG structure (by modifying the fracture pattern) is reported in the present work. The fatigue life of LG samples (having PVB interlayer of 0.76‐mm thickness) is evaluated using the standard method. Further, a theoretical explanation is presented for improved fatigue behaviour of LG. The effect of treatment of LG and cyclic bending fatigue load on cyclic fatigue strength is reported. The cyclic fatigue strength of LG increases 19.1% to 30.5% for treated LG samples when compared to untreated samples. The finite element model is developed (for treated and untreated LG) using the transient analysis in ANSYS 14.5 (Explicit Dynamics Module) to obtain the maximum deformation at failure load for the corresponding number of cycles. The strain‐life relations are established. The previously established fracture models and underdeveloped nanofracture mechanics concepts are used to explain the fracture patterns of the LG samples. Analysis of variance is conducted to ensure the validity of the experimental results.     

Simulation of crash tests for high containment levels of road safety barriers

This paper presents the results of computer simulations of road safety barrier behaviour under vehicle crash conditions for high containment levels as mandated by the European standard EN 1317. Simulations were performed with the explicit finite element code LS-DYNA, running on a multiprocessor computational platform. A very good agreement of simulation and real crash tests results was observed, which in turn justifies the use of computer simulations in the process of development and certification of road safety barriers.     

Computational and experimental crash analysis of the road safety barrier

The paper describes the computational analysis and experimental crash tests of a new road safety barrier. The purpose of this research was to develop and evaluate a full-scale computational model of the road safety barrier for use in crash simulations and to further compare the computational results with real crash test data. The impact severity and stiffness of the new design have been evaluated with the dynamic nonlinear elasto-plastic analysis of the three-dimensional road safety barrier within the framework of the finite element method with LS-DYNA code. Comparison of computational and experimental results proved the correctness of the computational model. The tests have also shown that the new safety barrier assures controllable crash energy absorption which in turn increases the safety of vehicle occupants.     

分子动力学模拟金属玻璃Cu应力晶化的应变率效应

采用Mishin镶嵌原子势，通过分子动力学方法模拟了零温下非晶金属Cu在不同应变率条件下的拉伸变形过程和应力晶化行为，分析了此过程中原子体系应力与结构组态的变化．结果表明：在应变率10^8s^-1-10^9s^-1范围内，金属玻璃Cu的塑性流动应力随着应变率的提高而增大，弹性模量约为55GPa．在塑性流动过程中发生应力晶化现象，伴随着明显的晶核形成与生长过程，晶化程度随着应变率的增加而加剧．应力效应和温度效应都是导致金属玻璃晶化的重要途径，形成的少量纳米晶粒是导致剪切带的形成和扩展的可能因素．     

Methodology to develop crash modification functions for road safety treatments with fully specified and hierarchical models

Crash modification factors (CMFs) for road safety treatments are developed as multiplicative factors that are used to reflect the expected changes in safety performance associated with changes in highway design and/or the traffic control features. However, current CMFs have methodological drawbacks. For example, variability with application circumstance is not well understood, and, as important, correlation is not addressed when several CMFs are applied multiplicatively. These issues can be addressed by developing safety performance functions (SPFs) with components of crash modification functions (CM-Functions), an approach that includes all CMF related variables, along with others, while capturing quantitative and other effects of factors and accounting for cross-factor correlations. CM-Functions can capture the safety impact of factors through a continuous and quantitative approach, avoiding the problematic categorical analysis that is often used to capture CMF variability. There are two formulations to develop such SPFs with CM-Function components – fully specified models and hierarchical models. Based on sample datasets from two Canadian cities, both approaches are investigated in this paper. While both model formulations yielded promising results and reasonable CM-Functions, the hierarchical model was found to be more suitable in retaining homogeneity of first-level SPFs, while addressing CM-Functions in sub-level modeling. In addition, hierarchical models better capture the correlations between different impact factors.     

Use of crash surrogates and exceedance statistics to estimate road safety

The limited ability of existing safety models to properly reflect crash causality has its source in cross-sectional analysis applied to the estimation of the intrinsically complex safety factors with highly aggregated and frequently poor quality of data. The adequacy of the data may be improved thanks to the unprecedented progress in sensing technologies and the invention of the naturalistic driving method of data collection. Proposed in this paper is a new modeling paradigm that integrates several types of safety models. The primary improvement results from a more adequate representation of the crash occurrence process by incorporating crash precursor events into the modeling framework. A Pareto-based estimating method for the likelihood of a collision occurrence, given a precursor event, is explained and illustrated with the simple example of road departures.     

A model for process-based crash simulation

Manufacturing of a bumper system from aluminium extrusions often involves series of forming operations performed in the soft W-temper condition, and then artificially age-hardening of the components to the material's peak hardness T6 condition. It is probable that proper finite element (FE) modelling of the crash performance of the resulting systems must rely upon a geometry obtained from an FE model following the process route, i.e., including simulation of all major forming operations. The forming operations also result in an inhomogeneous evolution of some internal variables (among others the effective plastic strain) within the shaped components. Results from tensile tests reveal that plastic straining in W-temper leads to a significant change of the T6 work-hardening curves. In addition, the tests show that the plastic pre-deformation causes a reduction of the elongation of the T6 specimens. In the present work, these process effects have been included in a user-defined elastoplastic constitutive model in LS-DYNA incorporating a state-of-the-art anisotropic yield criterion, the associated flow rule and a non-linear isotropic work hardening rule as well as some ductile fracture criteria. A first demonstration and assessment of the modelling methodology is shown by ‘through-process analysis’ of two uniaxial tensile test series. The industrial use and relevance of the modelling technique is subsequently demonstrated by a case study on an industrial bumper beam system.     

How the choice of safety performance function affects the identification of important crash prediction variables

Across the nation, researchers and transportation engineers are developing safety performance functions (SPFs) to predict crash rates and develop crash modification factors to improve traffic safety at roadway segments and intersections. Generalized linear models (GLMs), such as Poisson or negative binomial regression, are most commonly used to develop SPFs with annual average daily traffic as the primary roadway characteristic to predict crashes. However, while more complex to interpret, data mining models such as boosted regression trees have improved upon GLMs crash prediction performance due to their ability to handle more data characteristics, accommodate non-linearities, and include interaction effects between the characteristics.An intersection data inventory of 36 safety relevant parameters for three- and four-legged non-signalized intersections along state routes in Alabama was used to study the importance of intersection characteristics on crash rate and the interaction effects between key characteristics. Four different SPFs were investigated and compared: Poisson regression, negative binomial regression, regularized generalized linear model, and boosted regression trees. The models did not agree on which intersection characteristics were most related to the crash rate. The boosted regression tree model significantly outperformed the other models and identified several intersection characteristics as having strong interaction effects.     

Simulation of safety: A review of the state of the art in road safety simulation modelling

Recent decades have seen considerable growth in computer capabilities, data collection technology and communication mediums. This growth has had considerable impact on our ability to replicate driver behaviour and understand the processes involved in failures in the traffic system. From time to time it is necessary to assess the level of development as a basis of determining how far we have come. This paper sets out to assess the state of the art in the use of computer models to simulate and assess the level of safety in existing and future traffic systems. It reviews developments in the area of road safety simulation models. In particular, it reviews computer models of driver and vehicle behaviour within a road context. It focuses on stochastic numerical models of traffic behaviour and how reliable these are in estimating levels of safety on the traffic network. Models of this type are commonly used in the assessment of traffic systems for capacity, delay and general performance. Adding safety to this assessment regime may allow more comprehensive assessment of future traffic systems. To date the models have focused primarily on vehicular traffic that is, cars and heavy vehicles. It has been shown that these models have potential in measuring the level of conflict on parts of the network and the measure of conflict correlated well with crash statistics. Interest in the prediction of crashes and crash severity is growing and new models are focusing on the continuum of general traffic conditions, conflict, severe conflict, crash and severe crashes. The paper also explores the general data types used to develop, calibrate and validate these models. Recent technological development in in-vehicle data collection, driver simulators and machine learning offers considerable potential for improving the behavioural base, rigour and application of road safety simulation models. The paper closes with some indication of areas of future development.     

Modelling and optimization of proof testing policies for safety instrumented systems

This paper introduces a new development for modelling the time-dependent probability of failure on demand of parallel architectures, and illustrates its application to multi-objective optimization of proof testing policies for safety instrumented systems. The model is based on the mean test cycle, which includes the different evaluation intervals that a module goes periodically through its time in service: test, repair and time between tests. The model is aimed at evaluating explicitly the effects of different test frequencies and strategies (i.e. simultaneous, sequential and staggered). It includes quantification of both detected and undetected failures, and puts special emphasis on the quantification of the contribution of the common cause failure to the system probability of failure on demand as an additional component. Subsequently, the paper presents the multi-objective optimization of proof testing policies with genetic algorithms, using this model for quantification of average probability of failure on demand as one of the objectives. The other two objectives are the system spurious trip rate and lifecycle cost. This permits balancing of the most important aspects of safety system implementation. The approach addresses the requirements of the standard IEC 61508. The overall methodology is illustrated through a practical application case of a protective system against high temperature and pressure of a chemical reactor.     

Assessment of safety effects for widening urban roadways in developing crash modification functions using nonlinearizing link functions

Since a crash modification factor (CMF) represents the overall safety performance of specific treatments in a single fixed value, there is a need to explore the variation of CMFs with different roadway characteristics among treated sites over time. Therefore, in this study, we (1) evaluate the safety performance of a sample of urban four-lane roadway segments that have been widened with one through lane in each direction and (2) determine the relationship between the safety effects and different roadway characteristics over time. Observational before–after analysis with the empirical Bayes (EB) method was assessed in this study to evaluate the safety effects of widening urban four-lane roadways to six-lanes. Moreover, the nonlinearizing link functions were utilized to achieve better performance of crash modification functions (CMFunctions). The CMFunctions were developed using a Bayesian regression method including the estimated nonlinearizing link function to incorporate the changes in safety effects of the treatment over time. Data was collected for urban arterials in Florida, and the Florida-specific full SPFs were developed and used for EB estimation.     

Modelling and simulation of bulk metallic glass production process with suction casting

Abstract

An integrated model, which coupled nucleation and crystalline growth with the heat transfer process, is presented in the present paper. The temperature, temperature gradient, cooling rate and the crystalline fraction of Zr₆₅Al_7·5Cu_17·5Ni₁₀ in suction casting have been calculated with this model. The results show that the metallic glass can be obtained at the bottom and the radial boundary of the rod sample, and that the crystalline phase precipitates in the centre of the sample. The crystalline fraction reaches the highest value of 0·0128 in the centre of the sample. Comparatively lower nucleation rate, as well as the higher viscosity and the cooling rate account for the formation of the bulk metallic glass.     

Pedestrian crash estimation models for signalized intersections

The focus of this paper is twofold: (1) to examine the non-linear relationship between pedestrian crashes and predictor variables such as demographic characteristics (population and household units), socio-economic characteristics (mean income and total employment), land use characteristics, road network characteristics (the number of lanes, speed limit, presence of median, and pedestrian and vehicular volume) and accessibility to public transit systems, and (2) to develop generalized linear pedestrian crash estimation models (based on negative binomial distribution to accommodate for over-dispersion of data) by the level of pedestrian activity and spatial proximity to extract site specific data at signalized intersections. Data for 176 randomly selected signalized intersections in the City of Charlotte, North Carolina were used to examine the non-linear relationships and develop pedestrian crash estimation models. The average number of pedestrian crashes per year within 200 feet of each intersection was considered as the dependent variable whereas the demographic characteristics, socio-economic characteristics, land use characteristics, road network characteristics and the number of transit stops were considered as the predictor variables. The Pearson correlation coefficient was used to eliminate predictor variables that were correlated to each other. Models were then developed separately for all signalized intersections, high pedestrian activity signalized intersections and low pedestrian activity signalized intersections. The use of 0.25 mile, 0.5 mile and 1 mile buffer widths to extract data and develop models was also evaluated.     

Exploration and comparison of crash modification factors for multiple treatments on rural multilane roadways

As multiple treatments (or countermeasures) are simultaneously applied to roadways, there is a need to assess their combined safety effects. Due to a lack of empirical crash modification factors (CMFs) for multiple treatments, the Highway Safety Manual (HSM) and other related studies developed various methods of combining multiple CMFs for single treatments. However, the literature did not evaluate the accuracy of these methods using CMFs obtained from the same study area. Thus, the main objectives of this research are: (1) develop CMFs for two single treatments (shoulder rumble strips, widening shoulder width) and one combined treatment (shoulder rumble strips + widening shoulder width) using before–after and cross-sectional methods and (2) evaluate the accuracy of the combined CMFs for multiple treatments estimated by the existing methods based on actual evaluated combined CMFs. Data was collected for rural multi-lane highways in Florida and four safety performance functions (SPFs) were estimated using 360 reference sites for two crash types (All crashes and Single Vehicle Run-off Roadway (SVROR) crashes) and two severity levels (all severity (KABCO) and injury (KABC)).     

爆炸流场与玻璃幕墙动力响应的仿真计算方法

采用ALE有限元法进行了爆炸流场与复杂玻璃幕墙结构相互作用的三维动态仿真。针对数值仿真过程中计算效率过低的问题,根据显式有限元和距离爆炸冲击波试验问题的计算特点,利用高性能计算平台设计并实现了爆炸冲击波与玻璃幕墙动力响应的分步流固耦合仿真计算方法。研究了爆炸冲击波作用下幕墙玻璃的动力响应情况,通过与试验结果相比较,证实了该仿真方法的可行性,为玻璃幕墙结构的抗爆设计与改进提供了参考依据。     

风致飞掷物冲击建筑浮法玻璃试验和数值模拟

通过试验和有限元数值模拟的方法研究风致飞掷物对建筑浮法玻璃的冲击破坏效应。首先进行钢球冲击浮法玻璃面板的破坏试验,然后基于LS-DYNA建立与试验对应的飞掷物冲击浮法玻璃有限元模型,并通过对比试验和数值模拟的结果验证有限元模型的可靠性。最后基于验证后的有限元模型,以板状飞掷物为代表,研究风致飞掷物的冲击位置、冲击姿态和外形等特性对其冲击效应的影响。结果表明,建筑浮法玻璃在风灾中非常容易受到飞掷物的冲击而破坏。采用JH-2作为浮法玻璃的本构模型并以SIGP1=75 MPa作为失效准则,能够较准确地模拟浮法玻璃在冲击荷载下的破坏特性。板状飞掷物的冲击位置对其冲击效应影响不大,但其冲击姿态和边厚比对冲击效应有较大的影响。     

Experimental and simulation studies on fatigue behavior of laminated glass having polyvinyl butyral and ethyl vinyl acetate interlayers

Cyclic fatigue strength (CFS) of laminated glasses (LGs) with different interlayers and their different nominal thicknesses were compared. The effect of interlayer thickness, cyclic bending fatigue load, and interlayer type on CFS is clearly observed from this brief study. It was found that the LG‐PVB has comparatively lower CFS than LG‐EVA. There is an increment in CFS with an increment in critical interlayer thickness (significantly for an increment from 0.38 to 0.76 mm) in both LG‐EVA (prominent) and LG‐PVB. The maximum deformation at failure load at the corresponding number of cycles is obtained using the finite element model. The strain‐life relations for LG samples were established and shown by surface plots. The results of finite element analysis previously established fracture models were used to explain the fracture patterns of the LG samples. The conclusions of the study are useful for the selection of LG in fatigue prone LG structures.     

Safety performance functions for crash severity on undivided rural roads

The objective of this paper is to explore the effect of the road features of two-lane rural road networks on crash severity. One of the main goals is to calibrate Safety Performance Functions (SPFs) that can predict the frequency per year of injuries and fatalities on homogeneous road segments. It was found that on more than 2000 km of study-road network that annual average daily traffic, lane width, curvature change rate, length, and vertical grade are important variables in explaining the severity of crashes. A crash database covering a 5-year period was examined to achieve the goals (1295 injurious crashes that included 2089 injuries and 235 fatalities). A total of 1000 km were used to calibrate SPFs and the remaining 1000 km reflecting the traffic, geometric, functional features of the preceding one were used to validate their effectiveness. A negative binomial regression model was used. Reflecting the crash configurations of the dataset and maximizing the validation outcomes, four main sets of SPFs were developed as follows: (a) one equation to predict only injury frequency per year for the subset where only non-fatal injuries occurred, (b) two different equations to predict injury frequency and fatality frequency per year per sub-set where at least one fa tality occurred together with one injury, and (c) only one equation to predict the total frequency per year of total casualties correlating accurate percentages to obtain the final expected frequency of injuries and fatalities per year on homogeneous road segments. Residual analysis confirms the effectiveness of the SPFs.