We survey recent advances in algorithms for route planning in transportation networks. For road networks, we show that one can compute driving directions in milliseconds or less even at continental scale. A variety of techniques provide different trade-offs between preprocessing effort, space requirements, and query time. Some algorithms can answer queries in a fraction of a microsecond, while others can deal efficiently with real-time traffic. Journey planning on public transportation systems, although conceptually similar, is a significantly harder problem due to its inherent time-dependent and multicriteria nature. Although exact algorithms are fast enough for interactive queries on metropolitan transit systems, dealing with continent-sized instances requires simplifications or heavy preprocessing. The multimodal route planning problem, which seeks journeys combining schedule-based transportation (buses, trains) with unrestricted modes (walking, driving), is even harder, relying on approximate solutions even for metropolitan inputs.
Reinforced concrete (RC) beams strengthened with carbon-fabric-reinforced cementitious matrix (CFRCM) systems have shown potential for restoring flexural performance, yet their effectiveness under different corrosion levels remains insufficiently understood. This study presents a numerical investigation of the flexural behaviour of simply supported RC beams externally strengthened with CFRCM plates. Refined finite element models (FEMs) were developed by explicitly incorporating the steel–concrete bond-slip behaviour, the carbon fabric (CF) mesh–cementitious matrix (CM) interface, and the CFRCM–concrete substrate interaction and were validated against experimental results in terms of failure modes, load–deflection responses, and flexural capacities. A parametric study was then conducted to examine the effects of CFRCM layer number, steel corrosion level, and longitudinal reinforcement ratio. The results indicate that the baseline flexural capacity can be fully restored only when the corrosion level remains below approximately 15%; beyond this threshold, none of the CFRCM configurations achieved full recovery. The influence of the reinforcement ratio was found to depend on corrosion severity, while increasing CFRCM layers enhanced flexural performance but exhibited saturation effects for thicker configurations. In addition, corrosion level and CFRCM thickness jointly influenced the failure mode. Comparisons with design predictions show that bilinear CFRCM constitutive models are conservative, whereas existing FRP-based design codes provide closer agreement with numerical and experimental results.
[Objective] It is aimed to construct an evaluation index system for urban rail transit （URT） track structure health status based on comprehensive inspection vehicles， carrying out scientific evaluation of urban rail transit track structure health status， thereby providing a scientific basis for track structure maintenance and management. [Method] Leveraging the detection capabilities of urban rail comprehensive inspection vehicles， literature reviews， standard and specific analyses， and field investigations are conducted to identify the influencing factors of track structure health status. Following the scientificity， completeness， operability， hierarchy， and updatability principles， a preliminary evaluation index system for URT track structure health status is developed， consisting of 6 primary indicators and 40 secondary indicators. Based on this， a questionnaire survey is used to adjust and optimize the preliminary system， ultimately establishing a finalized evaluation index system for track structure health status based on urban rail comprehensive inspection vehicles. [Result & Conclusion] The constructed rail structure health status evaluation index system integrates existing academic research results， established standards and specifications， industry consensus and expert insights. It provides technical support for evaluating the health status of URT track structures and serves as a decision-making basis for their maintenance and management.
Collision avoidance between vehicles is a great challenge, especially in the context of mixed driving of connected and autonomous vehicles (CAVs) and human-driven vehicles (HVs). Advances in automation and connectivity technologies provide opportunities for CAVs to drive cooperatively. This paper proposes a proactive collision avoidance model, aiming to avoid collisions by controlling the speed and lane-changing behavior of CAVs. In the model, the subject vehicle first collects information about surrounding lanes and judges the traffic conditions; it then chooses to decelerate or change lanes to avoid collisions. The subject vehicle also searches for the optimal vehicle in the surrounding lanes for cooperation. The effectiveness of the proposed collision avoidance model is verified through the Python-SUMO platform. The experimental results show that the performance of the collision avoidance model is better than that of the cooperative adaptive cruise control (CACC) model in terms of average speed, lost time and the number of vehicle conflicts, proving the advantages of the proposed model in safety and efficiency.
CHEN Ziquan 1 , HE Chuan 1, YU Bingxin 1, LI Zheng 1, 2, ZHANG Hang 2, LIU Maoyi 2
The long-term structural safety issues of water-rich tunnels under complex hydrogeological conditions during operation period and their mutual interaction mechanism with groundwater environment are receiving increasing attention. To study the evolution process of seepage and stress field of urban tunnels with small interval and propose reasonable waterproof-drainage methods, the model tests and numerical studies on seepage are carried out based on the Kexuecheng Tunnel in Chongqing City. The evolution process of water and earth pressure on the lining structures is revealed. Subsequently, a proactive control technology for groundwater environmental protection based on the collaborative regulation of drainage and structural safety is proposed. The results indicate that the precipitation funnels formed by the left and right holes of urba tunnels with a small interval partially overlap and affect each other in space. The water pressure exhibits a W-shaped distribution in the horizontal direction, gradually evolving into a concave arc shape as the burial depth increases or decreases. The horizontal influence range of the seepage field and stress field exceeds 80 meters. The reduction effects of grouting circle on water pressure and surrounding rock pressure decrease with the increase of water head height. When the water head height is 30~50 m, the reduction ratio of grouting circle to the total load is about 18.6%~40%. The distribution of earth and water pressure of tunnels with small interval shows significant asymmetry. Under heavy rainfall conditions, the evolution process of the total load on the lining can be divided into three stages: slow growth, rapid growth and gradual stability phase. The secondary lining cracking and water inrush disasters caused by high water pressure are mainly concentrated at the haunch, arch foot and bottom of tunnel. For high water pressure sections of urban tunnels with small interval, it is recommended to add drainage blind pipes at the inverted arch. In ecologically sensitive areas, the active regulation technology should be adopted for groundwater discharge in tunnels to protect the ecological balance of groundwater environment.
Engineering geology. Rock mechanics. Soil mechanics. Underground construction
Magnesium potassium phosphate cement-based (MKPC) coating is regarded as an attractive green coating that improves the corrosion resistance of metals. Unfortunately, practical use remains challenging owing to the rapid solidification and hardening of MKPC coating. To overcome this issue, this work proposes a novel strategy to substitute a portion of potassium dihydrogen phosphate (KDP) with dipotassium hydrogen phosphate trihydrate (DKP) as phosphate source. Samples with or without KDP replacement were named KDP-DKP cement/coating and KDP cement/coating, respectively. The initial condensation time of KDP-DKP coating is more than 3 h, which is longer than that of KDP coating and can demand the actual construction needs. The anti-corrosion performance results display that protection efficiency (Pe%) of KDP-DKP coating is 95.33%, which is higher than 87.56% of KDP coating, indicating that the anti-corrosion performance of KDP-DKP coating is superior than that of KDP coating. Furthermore, durability and anti-corrosion mechanism of KDP-DKP coating were also investigated and explored through immersion and potentiodynamic polarization tests. The consequences demonstrate that KDP-DKP coating has excellent durability, and both magnesium and phosphate ions in the coating suppress the corrosion rate of Fe. In summary, this work developed a durable and eco-friendly MKPC coating, which provides feasible guidance for the practical application of MKPC anti-corrosion coating.
Abstract Hydrogen infrastructure for fueling vehicles has progressed in the last decade from stations with restricted access and limited operating hours to customer-friendly retail stations open to the public. There are now 121 retail hydrogen stations around the world. In California, the number of public retail hydrogen stations has increased from zero to more than 30 in less than two years, and the annual amount of hydrogen dispensed by retail stations has grown from 27,400 kg in 2015 to nearly 105,000 kg in 2016 and more than 440,000 kg in 2017—an increase of about four times year over year. For more than a decade, government, industry, and academia have studied many aspects of hydrogen infrastructure, from renewable hydrogen production to retail hydrogen station performance. This paper reviews the engineering and deployment of modern hydrogen infrastructure, including the costs, benefits, and operational considerations (including safety, reliability, availability), as well as challenges to the scale-up of hydrogen infrastructure. The results identify hydrogen station reliability as a key factor in the expense of operating hydrogen systems, placing it in the context of the larger reliability engineering field.
Purpose. Polymer products are used in industry due to their performance properties. The homogeneity of the melt is essential for the quality of the final product. Uniform distribution of components and properties ensures homogeneity of the product's physical and mechanical characteristics. Insufficient homogeneity can lead to defects in the product. The homogenization zone plays an important role in ensuring a homogeneous melt. In a disc extruder, the homogenization zone consists of four consecutive channels. In order to describe the flow for the entire homogenization zone, it is necessary to model the first channel first. Therefore, the main purpose of this work is to model hydrodynamic and thermal processes during the flow of a non-Newtonian fluid in a straight annular channel in a non-isothermal regime, as well as to create a general procedure for further calculations for other channels. Methodology. The analysis of publications was carried out. The procedure for calculating the velocity and shear rate of the longitudinal and tangential melt flow, the effective melt viscosity, and the calculation of the melt temperature change along the length of the annular gap in an analytical form was developed. Findings. In accordance with the developed procedure, the values of tangential and longitudinal velocities and shear rates were calculated. The graphical dependences of the distribution of tangential and longitudinal velocities and shear velocities of the melt flow along the width of the annular channel, the distribution of pressure and the temperature of the polymer melt averaged over the width of the gap along the length of the annular channel are presented. Originality. In this work, a stationary flow in a straight annular channel was modeled for LDPE of the 15803-020 grade in a non-isothermal regime. A general procedure for further calculations for other channels of the homogenization zone has been developed. Practical value. The given calculation procedure can be applied to the following channels of the homogenization zone, which allows describing the melt flow for the entire homogenization zone.
This study focuses on the psychological characteristics and empirically tests of the factors influencing distracted driving behaviours. This information is used as a reference for an intervention on dangerous driving behaviours. First, a distracted driving scale is constructed based on the theory of planned behaviour (TPB). The questionnaires are distributed in Chongqing, China, and 321 completed questionnaires are obtained. Data are analyzed using mean-variance analysis, one-way ANOVA, T-test, and multivariate test by SPSS 26.0 to determine the significance of distracted behaviours and demographic variables. We use a structural equation model to determine the path coefficients of each latent variable. Finally, we select the drivers with high tendency of distraction from the results of the questionnaires, conduct a four-stage rational emotional behaviour therapy (REBT) experiment, and use a repeated measures ANOVA analysis to test the validity and persistence of the intervention method. Results show that subjective norm is the most influential psychological factor. There are significant differences between the experimental group (2.38, SD = 0.41) and the control group (2.89, SD = 0.40) in the scores of distractions. This indicates that the distracted behaviour intervention achieves adequate validity and consistency. Educational research on distracted driving behaviour can help identify and correct drivers with high distraction tendency.
Transportation engineering, Transportation and communications
Under strong winds, the effect of sudden windbreak transition (WT) on high-speed trains is severe, leading to a deterioration of train aerodynamics and sudden yawing motion of the car body. To address these problems, based on a high-speed train and the specific geometric conditions derived from Xinjiang railway, first, the impact of a WT on the train and reasons for sudden changes in aerodynamic forces were determined by flow structural analysis. Furthermore, based on a multibody system dynamic model, the dynamic responses to WT were analysed. The results show that the impacts of WT were the strongest on the head car. WT had a strong effect on the train due to the unreasonable structural shape and the insufficient height of the windbreak in the transition region. This led to a strong push effect on the train; subsequently, the train’s dynamic characteristics deteriorated.
In this paper, a new class of broadband and low-loss transmission line called slotted rectangular waveguide (SRW) is proposed and analyzed. The proposed SRW consists of the rectangular waveguide and the inverted low-loss slotline, which can selectively suppress the higher-order mode (TE20 mode) and broaden the single dominant mode (TE10 mode) bandwidth in a rectangular waveguide (RW). The design principle and transmission characteristics of the SRW are illustrated and analyzed in this work. The transmission dominant mode bandwidth of the proposed SRW is analyzed and compared with the classic rectangular waveguide (RW), in which the dominant mode bandwidth of 60–155 GHz (88.4% bandwidth) is broader than the RW bandwidth of 60–116 GHz (63%). Two feed structures that can excite the two operating bandwidths (W and D band) of them separately are also designed. The SRW and transition exhibit broadband and low-loss characteristics from 75 GHz to 155 GHz, in which the transmission loss is lower than 0.68 dB and the return loss is over 18 dB.
Abstract Background ERTMS is an important project improving cross-border interoperability throughout Europe by a single rail signaling standard. One advantage following this development is a standardized radio signaling, which can be tracked by logging the data transfer using the ETCS protocol between Radio Block Center and train. This means that a broad spectrum of train driving can be analyzed in terms of for example driving behavior, signal planning and capacity in a new efficient way. Methods In this paper a radio-based protocol method to achieve this, is presented and applied for studying braking characteristics in terms of meeting point design. The aim was to design, apply and validate a radio-based train data collection method to enable cost-efficient and avoid time-consuming train data collections. To enable comparison between the results from the suggested radio-based method and traditional methods, a verification measurement was performed. Three different alternatives of speed calculation were validated. These were based on: Train Position Report speed; calculation of average speed based on reported train position; processed reported train position forming the average speed. The best alternative was then applied to examine deceleration towards different signal targets at single-track meeting points. Results The results from this study suggest that the ETCS Level 2 protocol is a feasible way to collect train dynamics data. The method is time saving when it comes to train driver behavior studies where several trains and drivers are needed to get significant results. Comparison with traditional GPS method suggest that the method is valid. Most promising is the alternative using processed train position.
Transportation engineering, Transportation and communications
Owing to its low cost and sustainable nature, lignocellulosic biomass has been utilized for reinforcing polymers, but it is crucial to understand the impact of high-ash concentrations in biomass on composite strength and processing. Biomass is not only desirable for biofuel production but could also have a strong market, if high-ash biomass is acceptable, for biocomposites. In this work, natural fibers (switchgrass and corn stover) were used to reinforce polylactic acid (PLA) to produce biocomposites. Natural fibers were pretreated to obtain fibers that contain different percentages of ash. The mechanical properties (such as Young's modulus, tensile strength, failure strain, storage modulus) of corn stover/PLA composites remained largely unaffected by the ash concentration of the biomass fibers, despite the large range of ash contents (2.2–11.9 wt%). However, the tensile strengths of switchgrass/PLA composites were slightly negatively affected by the ash concentration of the switchgrass fibers (0.7–2.1 wt%). Both the switchgrass/PLA and the corn stover/PLA composites exhibited a high-enough tensile strength (49–57 MPa) and suitable complex viscosity (2.0−7.0 kPa·s at the frequency of 3.2 rad/s). They are expected to be 3D-printable through an extrusion-based additive manufacturing process.
Materials of engineering and construction. Mechanics of materials
Abstract Both train rescheduling and station track assignment have become hot topics in recent years. It is fundamentally important to do the rescheduling and track assignment work at the same time to avoid the feasibility risk of the re‐scheduled timetable. The purpose of this paper is to design an integrated model for train rescheduling and track assignment in order to provide an integrative plan for the trains to run on the railway sections and go through stations. Based on the existing train rescheduling model, the model is designed by adding the constraints and the optimization goal of track assignment. The goal of track assignment is to maximize the equilibrium of the track usage time, and the constraint is that two trains cannot occupy a same track at the same time. An artificial bee colony algorithm is used to solve the model to get the operation plan. A computing experiment was carried out to prove the effectiveness of the model and the efficiency of the algorithm. The approach presented in this paper can provide a reference for the developers of a railway dispatching system.
Uncertainty, a critical factor of causing congestion and extra travel costs in the commute, can be mitigated by providing information. This paper studies the welfare effects of accurate pre-trip information on departure time and route choices in the morning commute under binary stochastic bottleneck capacity. We consider a classical two-route network. Each route has a single bottleneck where congestion occurs during the rush hours. The two routes' bottleneck capacities vary from day-to-day due to events such as bad weather, accidents, and temporary road closures. We derive all equilibrium solutions in consideration of the differences between routes in free-flow travel time, the shadow value of travel time, the severity of bottleneck capacity reductions, and the degree of correlation between two routes in travel conditions. Furthermore, we investigate the benefit changes from zero-information to full-information and prove that accurate pre-trip information about the bottleneck conditions is strictly welfare-improving. Finally, these theoretical results are supplemented by case studies that show examples of benefit gains from pre-trip information.