Study on the influence of skid resistance on traffic safety of highway with a high ratio of bridges and tunnels

ABSTRACT The safety of highways with a high ratio of bridges and tunnels is related to multiple factors, for example, the skid resistance of the pavement surface. In this study, the distribution of accidents under different conditions was calculated to investigate the relationship between the road skid resistance and the incidence of traffic accidents based on the traffic accident data of the Yuxiang highway. Statistical results show that weather conditions and road alignment may affect traffic accidents. The correlation analysis method was used to study the relationship between three factors and traffic accidents. The results show that road alignment, weather conditions and road skid resistance are related to the incidence of traffic accidents. The traffic accident prediction models were established based on back propagation neural network to verify the correlation analysis results. It is confirmed that road alignment, weather conditions and road skid resistance are the factors that affect traffic accidents.

Application of Biochar on the runoff purification performance of porous asphalt pavement

Biochar is currently applied in many low-impact development measures, such as biofilters and filter strips. However, its application in permeable pavement is limited. Due to the wide range of raw material sources, biochar may also contain nutrients and heavy metals. Whether its leachate will cause contamination during application remains unknown. Based on the static leachate contamination test, this study first evaluated the leachate contamination risks of three types of biochar and porous asphalt mixture (PA) with three biochar fillers. Through the pavement infiltration test, the purification performance of PA with biochar fillers and filter layers was further analysed. The results show that biochar contains nitrogen and phosphorus, and the leaching contamination of coconut shell is the most obvious; when the biochar is applied as a filler in PA, the leaching contamination decreases, while the pollutant purification performance is not obvious; when 3−5 mm rice straw biochar is used as a filter layer, the removal rate of total suspended solids can be 100%, but it is accompanied by more serious nitrogen and phosphorus leaching, and the greater the thickness, the more serious the degree of leaching. Deionized water cleaning can remove the phosphates contained in biochar, but have little effect on nitrogen. Therefore, before the application of biochar, cleaning measures should be taken to minimize its leaching contamination.

Physical and economic impacts of studded tyre use on pavement structures in cold climates

ABSTRACT In cold regions like Alaska of USA, Canada and the northern parts of Europe, using studded tyres is common among the public when driving in icy and snowy conditions. However, studded tyres cause extensive wear to asphalt pavement, reducing pavement life. This study addresses the physical and economic impacts of winter studded tyres on the roadway system to better inform decision makers as they develop alternative solutions and future polices. The approach is applied in a case study from a sample of Alaska statewide road segments. Surveys were employed to examine the extent of the use of studded tyres and cost-effective alternatives. A pavement life-cycle cost review was established considering several variables to discover a realistic cost of roadway resurfacing and rehabilitation. Wear rates due to studded tyres and rut rates due to wheel loads were found for different highway classes. The results indicate higher average wear rates due to studded passenger vehicles on freeways than average rut rates due to heavy wheel loads. The results also indicate lower average wear rates on arterial and collector roads. The estimates show that studded tyre use reduced asphalt surface life by about 7 years on the selected freeway sample in the case study, which is about 47% loss in pavement life based on the initial design life of 15 years. Other road classes experienced lower reductions in service life. Finally, cost analysis was provided to reflect the impact of studded tyres on the state's budget. Countermeasures were suggested, which in turn may help other cold regions develop strategies on the use of new winter tyre technology.

Study on the effect of dimple position on drag reduction of high-speed maglev train

Transient numerical simulations were carried out by placing dimples at the top, sides and bottoms of the tail car streamline area of a high-speed maglev train. The results of an improved delayed detached eddy simulation turbulence model using three-dimensional compressible Navier-Stokes and shear-stress transport K-Omega double equations were compared to the results of a wind tunnel test to verify the numerical simulation accuracy, within 5% of the ground truth, which is an acceptable precision range. The results show that dimples arranged on the streamline area atop the train tail car affected the locations at which the airflow at the top and bottom of the train met and weakened the strength of the wake. The aerodynamic drag and lift coefficient decreased by 3.40% and 4.27%, respectively. When the dimples were arranged on the streamline area at the sides or bottoms of the train tail car, they had little effect on the top of the tail car, so they did not destroy the balance of the airflow at the top and bottom. They also had little influence on the development of wake topology. Therefore, the aerodynamic drag and lift of the train changed little.

Design theories and maintenance technologies of slab tracks for high-speed railways in China: a review

The durability and reliability of slab track structures are essential for the long-term safety and stable operation of high-speed railways. In order to provide a solid theoretical basis and technical reference for the advancement of high-speed railway quality, this paper comprehensively discusses design theories of slab track structures, service performance evolution and maintenance technologies, and reviews the innovation happening in the industry. On top of that, the damage evolution, fatigue features and durability of slab tracks, which are highly relevant to serviceability, are summarized, and the future research trend of slab track service behaviours is pointed out. In addition, this paper summarizes the rules of establishing standards for damage maintenance, typical solutions for repairing damage and methods of evaluating the maintenance outcomes that combine field tests and numerical simulations. It also envisions a future direction where advanced testing technologies would assist the evaluation of maintenance effects.

Experimental study on the effect of canyon cross wind on temperature distribution of buoyancy-induced smoke layer in tunnel fires

Experiments were conducted in a 1:20 arced tunnel model to investigate the effect of canyon cross wind on buoyancy-induced smoke flow characteristics of pool fires, involving smoke movement behaviour and longitudinal temperature distribution of smoke layer. The canyon wind speed, longitudinal fire location and fire size were varied. Results show that there are two special smoke behaviours with the fire source positioned at different flow field zones. When the fire source is positioned at the negative pressure zone, with increasing canyon wind speed, the smoke always exists upstream mainly due to the vortex, and the smoke temperature near the fire source increases first and then decreases. However, when the fire source is located in the transition zone and the unidirectional flow zone, there is no smoke appearing upstream with a certain canyon wind speed. Meanwhile, the smoke temperature near the fire sources are decreases with increasing canyon wind speed. The dimensionless temperature rise of the smoke layer ΔTs* along the longitudinal direction of the tunnel follows a good exponential decay. As the canyon wind speed increases, the longitudinal decay rate of ΔTs* decreases. The longitudinal decay rate of ΔTs* downstream of the fire is related to the fire location and canyon wind speed, and independent of the fire size. The empirical correlations for predicting the longitudinal decay of ΔTs* downstream of the fire are established. For a relatively large-scale fire, the longitudinal decay rate of ΔTs* upstream of the fire increases as the distance between the fire source and the upstream portal increases, especially for larger canyon wind speeds.

Investigation on mechanical properties and water stability of porous polyurethane concrete

Porous polyurethane concrete (PPUC) is a novel material for permeable pavements and is considered as an alternative to porous asphalt or porous cement concrete. However, studies of the mechanical properties of PPUC are still insufficient. In this study, the comprehensive mechanical properties and water stability of PPUC with different gradations and polyurethane dosages were investigated, and its water damage mechanism was preliminarily explored. The results show that the flexural strength and Marshall stability of PPUC can more easily reach the index in the standards of porous cement concrete or porous asphalt, while the compressive strength and abrasion resistance are the weak points of its mechanical properties and need to be further optimized. The mechanical properties and water stability of PPUC were effectively improved by increasing the polyurethane dosage and using continuously graded aggregates. PPUC is more susceptible to water damage because water reacts with the residual isocyanate groups within the polyurethane film to generate carbon dioxide gas, which reduces the cohesion and adhesion performance of polyurethane film. This study provides a comprehensive understanding of the mechanical properties of PPUC and an initial insight into the mechanism of water damage.

Key points of investigation and analysis on traffic accidents involving intelligent vehicles

Intellectualization is regarded as the future mainstream development trend of the automobile industry. The automation level of intelligent vehicles is relatively low so far, and the road traffic system will be in a mixed state of non-autonomous vehicles and vehicles with different levels of automation for a long time. Therefore, the road traffic system will be more complex with more diverse accidents. This paper analysed the characteristics and causal factors of intelligent vehicle accidents. Based on the problems existing in investigation, analysis and liability identification of intelligent vehicle accident, the study proposed a preliminary accident investigation framework and method, summarized the key points of accident analysis from the perspectives of technical defects, information security and passive safety, and specified the liability subjects for intelligent vehicle accidents and their corresponding legal liability. The results from this study contributed to the development of intelligent vehicle accident investigation and disposal, and provided the reference for the improvement of vehicle safety and accident prevention.

A high-fidelity human cervical muscle finite element model for motion and injury studies

Active muscle response is a key factor in the motion and injury of the human head and neck. Due to the limitations of experimentation and the shortcomings of previous finite element models, the influence of material parameters of cervical muscle on motions of the head and neck during a car crash have not been comprehensively investigated. In the present work, a model of the cervical muscle in a 50th-percentile adult male was constructed. The muscles were modelled using solid finite elements, with a nonlinear-elastic and viscoelastic material and a Hill material modelling the passive and active parts of each muscle, respectively. The head dynamic responses of the model were validated using results obtained from volunteer sled tests. The influence of the material parameters of a muscle on head and neck motions were determined. Our key finding was that the greater the stiffness and the contraction strength of the neck muscles, the smaller the rotation angle of the head and the neck, and, hence, the lower the risk of head and neck injury to occupants in a car crash.

Natural disaster warning system for safe operation of a high-speed railway

In this paper, the least square support vector machine (LSSVM) is used to study the safety of a high-speed railway. According to the principle of LSSVM regression prediction, the parameters of the LSSVM are optimized to model the natural disaster early warning of safe operation of a high-speed railway, and the management measures and methods of high-speed railway safety operation under natural disasters are given. The relevant statistical data of China's high-speed railway are used for training and verification. The experimental results show that the LSSVM can well reflect the nonlinear relationship between the accident rate and the influencing factors, with high simulation accuracy and strong generalization ability, and can effectively predict the natural disasters in the safe operation of a high-speed railway. Moreover, the early warning system can improve the ability of safety operation evaluation and early warning of high-speed railway under natural disasters, realize the development goals of high-speed railway (safety, speed, economic, low-carbon and environmental protection) and provide a theoretical basis and technical support for improving the safety of a high-speed railway.