Time and Distance Gaps of Primary-Secondary Crashes Prediction and Analysis Using Random Forests and SHAP Model

Secondary crashes (SCs) are typically defined as the crash that occurs within the spatiotemporal boundaries of the impact area of the primary crashes (PCs), which will intensify traffic congestion and induce a series of road safety issues. Predicting and analyzing the time and distance gaps between the SCs and PCs will help to prevent the occurrence of SCs. In this paper, a combined data-driven method of static and dynamic approaches is applied to identify SCs. Then, the random forests (RF) method is implemented to predict the two gaps using temporal, primary crash, roadway, and real-time traffic characteristics data collected from 2016 to 2019 at California interstate freeways. Subsequently, the SHapley Additive explanation (SHAP) approach is employed to interpret the RF outputs. The results show that the traffic volume, speed, lighting, and population are considered the most significant factors in both gaps. Furthermore, the main and interaction effects of factors are also quantified. High volume possibly promotes the time and distance gaps, while low volume inhibits them. And volume affects the distance gap inconsiderably when it falls between 300 and 400 veh/5 min. Traffic conditions with high speed and low volume are strongly associated with short-time and short-distance gaps. Darker surroundings probably accelerate the occurrence of SCs. Moreover, crashes involving the violation categories of improper turns or unsafe lane changes likely result in long time and distance gaps. These results have important implications for proposing traffic management and improving road safety

In situ characterization of high-temperature mechanical behaviors of freestanding Si, BSAS and Yb2SiO5 environmental barrier coatings by three-point bending tests based on digital image correlation

The high-temperature mechanical properties and failure mechanisms of Si, BSAS and Yb2SiO5 ceramic materials are important for environmental barrier coatings. The Si coating, BSAS coating and Yb2SiO5 coating were prepared by the atmospheric plasma spray (APS) technique. The elastic modulus, fracture strength and fracture strain are determined by three-point bending combined with the digital image correlation (DIC) method. The results show that as the test temperature increases from 25 °C to 1000 °C, the elastic modulus of the Si coating and Yb2SiO5 coating decreases while the elastic modulus of the BSAS coating increases. And the fracture strength and fracture strain of the Si coating, BSAS coating and Yb2SiO5 coating increase. The elastic modulus is related to the interatomic distance and bonding strength of atoms. The fracture strength and fracture strain increase with the densification of the coating

Cu2+-Ion-Substitution-Driven Microstructure and Microwave Dielectric Properties of Mg1−xCuxAl2O4 Ceramics

In this work, Cu-substituted MgAl2O4 ceramics were prepared via solid-state reaction. The crystal structure, cation distribution, and microwave dielectric properties of Mg1−xCuxAl2O4 ceramics were investigated. Cu2+ entered the MgAl2O4 lattice and formed a spinel structure. The substitution of Cu2+ ions for Mg2+ ions contributed to Al3+ ions preferential occupation of the octahedron and changed the degree of inversion. The quality factor (Qf) value, which is correlated with the degree of inversion, increased to a maximum value at x = 0.04 and then decreased. Ionic polarizability and relative density affected the dielectric constant (εr) value. The temperature coefficient of the resonant frequency (τf) value, which was dominated by the total bond energy, generally shifted to the positive direction. Satisfactory microwave dielectric properties were achieved in x = 0.04 and sintered at 1550 °C: εr = 8.28, Qf = 72,800 GHz, and τf = −59 ppm/°C. The Mg1−xCuxAl2O4 solid solution, possessing good performance, has potential for application in the field of modern telecommunication technology