Abstract:To investigate the dynamic characteristics of underwater explosion bubbles under cylindrical shell structure,an experimental system for bubble pulsation and jet under cylindrical shell is designed.Bubbles are generated using an electric spark generation device,and bubble dynamic characteristic images are captured by a high-speed camera.Pressure sensors are employed to collect data on pressure load variations at the bottom wall of the cylindrical shell,and the influence of the dimensionless parameter γ on the peak pressure and duration of bubble loads are analyzed.Experimental results indicate that when γ is 0.25 and 0.50,the bubble shape is inverted mushroom-shaped to cumulous-shaped;when γ is 0.75 and 1.00,the bubble shape is columnar to cumulous-shaped;when γ is 1.25 and 1.50,the bubble shape exhibits egg-shaped to fan-shaped morphology.For 0.25≤γ≤1.50,the peak pressure of bubble shock wave load decreases with increasing γ,while the duration of shock wave load peak pressure increases with increasing γ;the duration of peak pressure from the first-cycle pulsation and jet load is greater than that of the second-cycle pulsation and jet load.For 0.25≤γ≤0.75,the peak pressures of both first-cycle and second-cycle pulsation and jet loads decrease with increasing γ;for 0.75<γ≤1.00,the peak pressures of both first-cycle and second-cycle pulsation and jet loads increase with increasing γ;for 1.00<γ≤1.50,the peak pressure of first-cycle pulsation and jet load decreases with increasing γ,while the peak pressure of second-cycle pulsation and jet load increases slowly with increasing γ.

Abstract:To address the issues of low additive utilization poor low temperature and fatigue performance in high modulus asphalt mixture,for direct application,a self-reactive high modulus asphalt and asphalt mixture are prepared using low-density ethylene-styrene copolymer-based high-modulus agents,and their technical performance is evaluated.Three kinds of self-reactive high modulus asphalt are prepared with rather lower content(6%,7% and 8%)of low-density ethylene-styrene copolymer as high modulus agent by pure mixing process,then the dispersion state and modification mechanism of high modulus agent are analyzed based on microscopic and physicochemical properties.The reasonable content of high modulus agent is selected based on the results of macroscopic performance test.Furthermore,the high modulus asphalt mixture with the preferred modifier content is prepared and its pavement performance is evaluated by laboratory tests.Results show that the modification process of self-reactive high modulus asphalt is a combination of the physical action of the high modulus agent and the chemical reaction between the asphalt binder and the modifier.The preferred high modulus agent content is 7%(by mass of the asphalt),which is 50%-80% of the modifier content in the dry-process.In this condition,the microscopic dispersion effect of the high modulus agent and the low-temperature performance of high modulus asphalt are desirable,and the PG high-temperature grade of high modulus asphalt is improved by one grade compared with that of the conventional high modulus asphalt.In addition to its superior high temperature performance,the high modulus asphalt mixture with optimum modifier content exhibited an 18%improvement in low-temperature destructive strain relative to conventional high modulus asphalt mixture with dry-process,while also achieving a 2 to 3 times extension in fatigue life.

Abstract:To fully leverage the wave-absorbing and heating properties of iron ore tailings and achieve high-value utilization of mining solid waste,this study incorporates iron ore tailings into cement concrete as coarse aggregates to investigate the damage patterns of iron ore tailing concrete under microwave irradiation.X-ray diffraction(XRD)phase analysis is performed on iron ore tailing particles to study the microwave heating mechanism.The temperature changes of iron ore tailing particles and concrete,as well as the ultrasonic pulse velocity(UPV)variations of iron ore tailing concrete before and after microwave irradiation,are analyzed.Scanning electron microscopy(SEM)is employed to observe the surface morphology and microstructure of the concrete before and after irradiation to investigate internal micro-damage.The results indicate that the iron-containing oxides in iron ore tailings possess superior wave-absorbing capabilities.The temperatures of both iron ore tailings and limestone increase with irradiation time,while the heating rate decreases;however,the temperature rise of iron ore tailings is larger than that of limestone.At the same irradiation time,the temperature of iron ore tailing concrete increases with increasing power.The wave-absorbing efficiency is highest at 6 kW.The temperature difference of the specimens before and after irradiation increases linearly at first and then slows down with increasing irradiation time.The UPV of the concrete decreases with increasing irradiation time and power.At the same power,the UPV attenuation rate increases rapidly initially and then slows down with increasing time.Under 0、2、4、6,8 kW power and 0～5 min irradiation,the UPV attenuation rate can reach up to 35.29%.After microwave irradiation,1～3 μm thermal stress cracks are generated in the interfacial transition zone between iron ore tailings and mortar and propagate along the interface.

Abstract:To predict the stability conditions of the support structure and achieve effective early warning,finite element software MIDAS CIVIL is used to model the pin-supported disc-type supports of the bridge,simulating the response characteristics of the support structure under single-point settlement and regional settlement conditions.Using in-situ testing methods on the bridge,a comparative analysis is conducted between the simulated data and the actual measurement data of the support deformation,demonstrating the feasibility of using angular change thresholds to monitor the preloading and pouring processes,and acquiring the deformation patterns at critical positions of the supports.The results show that the deformation data measured by the gyroscope closely match the simulated data,and the angular change threshold for construction process monitoring is feasible.Insufficient foundation bearing capacity leads to three different settlement conditions:first,when the single-point foundation bearing capacity is insufficient,forced displacements are applied to the four corner support rods at the bottom plane of the middle part of the support structure,resulting in significant angular changes at four measurement points,but none exceeds the warning threshold;settlement occurred at the position where the largest reaction force from the support is applied at the bottom of the support;second,when the foundation bearing capacity is insufficient in certain areas,forced displacements are applied to the middle,left,and right parts of the support structure,significantly affecting the key monitoring sections,with noticeable changes in local structural displacements;the angular changes remain within the permissible thresholds,and the reduction rates of displacement and angle during the pouring condition show minimal variation;third,when the foundation bearing capacity at the bottom of the members where each measurement point is located is insufficient,simultaneous node displacements are applied to the bottom nodes of the monitoring sections,with major settlement occurring in the regions around the bottom of the measurement points;the angular threshold increases with the increase in load,validating the effectiveness of the settlement identification and early warning method based on angular thresholds.

Abstract:To analyze the stress conditions of bridge deck panels with different stiffener forms in steel box girders,the software ANSYS is used to establish a comprehensive model and a spatial shell local model for a single box double-chamber continuous steel box girder with a span of(32+40+32)m.The effects of the main girder system and bridge deck system are obtained,and a comparative analysis is conducted on the structural effects of commonly used open section(inverted T-shaped)stiffeners and closed section(U-shaped)stiffeners in bridge deck panels.The results indicate that:1)The overall model reveals that the stress situation of the main girder system in the steel box girder,under basic combination effects and fatigue load effects,shows that the displacements and stresses of the bridge deck panels with inverted T-shaped stiffeners and U-shaped stiffeners are quite similar.2)Under local vehicle load,the longitudinal and transverse stresses of the inverted T-shaped stiffener bridge deck panel are more than twice those of the U-shaped stiffener bridge deck panel;the maximum longitudinal stress of the inverted T-shaped stiffener is greater than that of the U-shaped stiffener,while the vertical shear stress is smaller than that of the U-shaped stiffener and is lower than that of the bridge deck panel;the transverse and vertical stresses of the U-shaped stiffener steel box girder web are significantly increased compared to the inverted T-shaped stiffener,with a maximum increase of about 3.5 times.In design,adjustments should be made to the stiffness of the longitudinal and transverse stiffeners to ensure balanced stress in all components;the local deformation trends of the bridge deck panels in the inverted T-shaped and U-shaped stiffener models are similar,but the local deformation of the bridge deck panel under the inverted T-shaped stiffener model is larger than that of the U-shaped stiffener model,approximately 1.2 times the displacement of the latter.

Abstract:To address the problems of high scene complexity,difficult recognition,and high false detection rate in detecting abnormal behavior of object passing through subway station barriers,a detection method is proposed that data fusion based on light detection and ranging(LiDAR)and camera sensors.A voxel difference algorithm is used to process LiDAR point cloud data,divide the detection area into voxel units,and establish a trigger mechanism for object passing.An object locking algorithm is employed to fuse data collected by LiDAR and cameras,supplementing depth information of human key points and locking onto target of object passing through barriers.The spatial-temporal graph convolutional network(STGCN)is lightweight-modified to reduce model complexity and computation time.A temporal trend attention(TTA)model is introduced to enhance the extraction of spatial-temporal feature changes in postures of object passing through barriers,forming the TTA-STGCN model to calculate the confidence of behavior occurrence of object passing through barriers.Collecting data of object passing through barriers through laboratory simulation and on-site in subway stations.Detection performance evaluation metrics are established.Training,validation,and testing of STGCN,STGCN-MIN,and TTA-STGCN models are conducted.In the training phase,the accuracy of the TTA-STGCN model improved by 3.73%compared to the first two,the overall loss decreased by 66.00%.In the validation phase,the accuracy of the TTA-STGCN model improved by 3.89%and 0.68%compared to the first two respectively,the overall loss decreasing by 58.95%and 58.48%respectively.In the testing phase,the accuracy of the TTA-STGCN model improved by 3.15%compared to the first two,the overall loss decreasing by 42.85%and 44.40%respectively.Field experiments show that the TTA-STGCN model's accuracy improved by 2.99%and 3.49%compared to STGCN-MIN and STGCN models respectively,precision improved by 2.28%and 1.31%respectively,recall improved by 4.30%and 6.45%respectively,and F1 score improved by 0.033 5 and 0.040 4 respectively,demonstrating that the TTA-STGCN model significantly enhances the detection accuracy of behavior of object passing through barriers in specific subway station scenarios.

Abstract:To address issues such as large volume,heavy weight,and low adsorption force of permanent magnetic wheel in wall-climbing robot,the design aims to reduce the wheel mass and increase adsorption force.Combining lightweight design methods,the magnetic disks on both sides of the permanent magnetic wheel are designed by structural optimization.Electromagnetic field simulation software ANSYS Maxwell is used to model and simulate the permanent magnetic wheel,obtaining the magnetic field line distribution.By reducing the magnetic material in areas with sparse field lines and increasing it in dense areas,the wheel's adsorption force is enhanced.Through adjusting the main structural parameters of the magnetic disk and simulating the adsorption force changes between the permanent magnetic wheel and ferromagnetic wall surface,the optimal structural parameters for maximum adsorption force are determined.Simulation and physical tests verify the adsorption force of the optimized magnetic disk.Results show that the magnetic disk mass is 232.53 g,reduced by 16.24%;the simulated adsorption force between the permanent magnetic wheel and ferromagnetic wall is 487.65 N,increased by 20.74%;50 pull tests of the permanent magnetic wheel all exceed the simulated adsorption force,with an average of 493.83 N.The results show that after structural optimization,the mass and adsorption force indicators of the permanent magnet rotor meet the design objectives.

Abstract:To address the congestion problems caused by saturated and oversaturated traffic flow at urban road intersections and improve the efficiency of intersection traffic flow organization,an optimization method for traffic flow organization at pre-signal controlled intersections is proposed.Based on the channelization design of intersection approach lane and the coordination of main and pre-signal phase sequences,this method aims to improve the efficiency of left-turn and through traffic flows at intersection approaches and the utilization of intersection temporal and spatial resources.Two operation modes are designed for left-turn and through phases at approaches that continuous release mode and separate release mode.Experimental validation is conducted.Results indicate that:under different traffic volumes at intersection approach lane,pre-signal controlled intersections have smaller average signal cycle times,mean vehicle delays,and rates of increase in average vehicle delay with increasing approach lane traffic volume compared to traditional single-stop-line intersections,the separate release mode of pre-signal controlled intersections performs better than the continuous release mode in terms of average signal cycle times,mean vehicle delays,and rates of increase in average vehicle delay with increasing approach lane traffic volume;under the separate release mode of pre-signal controlled intersections during traffic flow saturated or oversaturated conditions on intersection approach lane,average vehicle delay time is minimized.

Abstract:To address the local optimum problem of the traditional artificial potential field(T-APF)algorithm and the limitations of dynamic obstacle avoidance in emergency collision avoidance scenarios for autonomous vessels,an enhanced artificial potential field(E-APF)algorithm based on time to closest point of approach(TCPA)and distance to closest point of approach(DCPA)is proposed.This algorithm reconstructs the repulsive potential field function,introduces a dynamic weight adjustment mechanism,and combines relative motion dynamics to design an adaptive repulsive direction strategy.Simulation results indicate that in static obstacle scenarios,the E-APF algorithm can identify collision risks earlier and plan better paths compared to the T-APF algorithm;in dynamic obstacle scenarios,it effectively increases safety distances and reduces steering angles,significantly improving the accuracy of obstacle risk assessment and collision avoidance decision-making.

Abstract:To accurately simulate the regenerative braking conditions of micro electric vehicles,a regenerative braking test system model is developed using MATLAB/Simulink.The simulation analyzed regenerative braking performance and calculated the regenerative efficiency of the drive motor under forced braking and gentle braking modes.The results show that when the accelerator pedal opening reaches 95%,the regenerative efficiencies under forced and gentle braking modes are 60.3%and 14.6%,respectively,which align closely with the target values of 60.0%and 15.0%.Additionally,higher braking deceleration and longer regenerative braking duration lead to greater recovered energy.The forced braking mode of the drive motor can significantly increase regenerative energy,thereby extending the driving range of micro electric vehicles.

Abstract:To reflect the actual state of the unsaturated three-phase medium of the subgrade,the subgrade is regarded as an unsaturated porous medium with incompressible solid and liquid phases,and a compressible gas phase.Based on the representation method of unsaturated porous media,considering the effects of inertia,viscosity,and mechanical coupling,a dimensionless one-dimensional wave equation for the unsaturated subgrade is established.Taking a type of non-homogeneous boundary as an example,the problem is transformed into an initial value problem of a second-order ordinary differential equation through boundary homogenization and the method of characteristic functions,and the state-space method is used to obtain the exact solution of the one-dimensional transient response of a single-layer unsaturated subgrade.The correctness of the results is verified through numerical examples.The characteristics of the one-dimensional transient response of the single-layer unsaturated subgrade under step and sinusoidal loads are analyzed.The results show that,unlike compressible saturated and unsaturated soils,there is only one type of compression wave in the incompressible unsaturated subgrade.As the liquid phase saturation increases,the wave speed and vibration amplitude of the compression wave decrease.The conclusion can provide a reference for the optimal design and disaster prevention of unsaturated subgrades under complex environmental loads.

Abstract:To measure smart logistics efficiency in the Beijing-Tianjin-Hebei Region,panel data on input indicators,output indicators,and influencing factors from 2013 to 2022 are utilized.The data envelopment analysis(DEA)model is applied to calculates technical efficiency,pure technical efficiency,and scale efficiency of regional smart logistics.The Tobit model is used to analyzes the impact intensity of economic development level,industrial factors,energy utilization rate,digital sales revenue,and internet development level on smart logistics efficiency.Recommendations for enhancing efficiency are proposed.Results indicate:during the period 2013 to 2022,Beijing′s smart logistics technical efficiency shows stage-wise leaps,continuously increasing from 2013 to 2015 and remaining efficient after 2016 except 2021;Tianjin achieves efficiency in 8 a,with inefficiency only in 2015 and 2019;Hebei achieves efficiency in 7 a,with inefficiency in 2015,2016,and 2020;low pure technical efficiency primarily causes inefficiency in Beijing while low scale efficiency dominates in Hebei;economic development level,industrial factors,and digital sales revenue exhibit significant positive effects on smart logistics efficiency,whereas energy utilization rate and internet development level show insignificant impacts.Recommendations include optimizing industrial structure,strengthening economic drivers,and advancing smart logistics development.

Abstract:To address issues such as poor stability,large trajectory tracking errors,and complex control strategies in the actual operation of two-wheeled self-balancing robot(TWSBR),the dynamics and kinematics of TWSBR are analyzed and a mathematical model is established.A forward control system is designed based on the linear quadratic regulator(LQR),and a steering control system is designed based on the sliding mode variable structure controller(SMVSC).Simulation experiments are conducted on the LQR forward control system and SMVSC steering control system.Simulation results show that:the actual steering angle of TWSBR reaches the desired steering angle after 1.2 s,the actual body tilt angle reaches the desired body tilt angle after 2 s,and the actual speed reaches the desired speed after 3 s.A trajectory tracking generator is designed,and a TWSBR trajectory tracking control system is constructed,and a TWSBR experimental platform is built.TWSBR trajectory tracking experiment is conducted.The experimental results show that the errors of TWSBR body tilt angle,body tilt angular velocity,steering angle,and steering angular velocity stabilize near 0 after 1 s,while the displacement error and speed error stabilize near 0 after 2 s.The fluctuation range of each state variable of TWSBR is small after stabilization.Considering factors such as sensor acquisition errors and motor drive precision,the results indicate that the TWSBR demonstrates good trajectory tracking performance,and achieves displacement tracking,speed tracking,body tilt angle tracking,and steering angle tracking.

Abstract:In the context of global warming and resource scarcity,promoting sustainable transportation is a vital component of the green transformation of socio-economic systems.Yet,no universal consensus has been reached on the definition of sustainable transportation,and systematic reviews of its current development remain limited.This paper provides a comprehensive review of both the conceptual foundation and the current state of sustainable transportation.First,it traces the historical evolution of the concept.Second,it synthesized and compared definitions proposed by international organizations and national or regional authorities.Sustainable transportation is herein defined as an innovative development model that minimizes environmental impacts,such as carbon emissions,air pollutants,and noise,reduces energy consumption,and integrates economic growth,social well-being,traffic safety,and equity,thereby preserving resources and opportunities for future generations.Third,the research priorities of 16 leading international and national institutions in the field are systematically reviewed.Finally,current progress summarized in terms of six key technological advances and four developmental models,with major challenges and issues identified.The findings provide theoretical insights and strategic guidance for the future advancement of sustainable transportation.

Abstract:To address the issues of high porosity and low resource utilization efficiency of steel slag,a micropore filling technology is proposed.Based on the principle of pneumatic driving,the gas-liquid replacement process within the pores of steel slag is optimized,allowing the cement slurry to be efficiently and stably injected into the micropores of the steel slag.The quality increment of the steel slag before and after filling is tested under different pressure application methods,pressure application times,water-cement ratios,experimental temperatures,and steel slag particle sizes,studying the impact of micropore filling technology on the porosity of steel slag.The results indicate that with an increase in pressure application time,the overall mass increment of the steel slag increases.Negative pressure filling offers both safety and efficiency advantages;at 4 minutes of pressure application,the mass increment of steel slag filled under negative pressure is 20%greater than that of positive pressure.The final filling quality of the two pressure application methods tends to be the same,approximately 0.45 g.The high viscosity and poor fluidity of the cement slurry cause the mass increment of the steel slag to initially decrease and then slightly increase as the water-cement ratio increases.When the water-cement ratio is 0.8,the mass increment of the steel slag is 4.5 times than that at a water-cement ratio of 2.0.Increasing the experimental temperature from 25 ℃ to 50 ℃ accelerates the hydration agglomeration of the cement,resulting in a 37.5%decrease in the mass increment of the steel slag and a significant reduction in filling efficiency.The filling effect is most pronounced when the steel slag particle size is>5-10 mm,with a mass increment of 0.16 g.By filling the pores of the steel slag with cement products,interfacial homogenization can be achieved,significantly reducing porosity and improving gas-liquid replacement efficiency.

Abstract:To accurately monitor the dynamic response of surrounding rock and support structures during tunnel construction and early operation phases,promptly identify potential instability risks,validate design rationality,and guide safe construction practices,systematic and high-precision on-site monitoring methods are implemented.Total station instruments are employed for continuous non-contact measurement of tunnel crown settlement,surrounding convergence,and surface settlement to precisely capture spatial deformation.Combined with geophysical radar for early detection of adverse geological formations ahead,automated data acquisition systems and specialized analysis software enable real-time transmission,processing,visualization,and early warning analysis of massive monitoring data.Post-excavation monitoring data indicate that the deformation of the surrounding rock after tunnel excavation follows a three-stage change pattern,transitioning from rapid change to slow change and finally to basic stability as construction progresses.This validates the applicability of the designed support parameters in most sections,but indicates insufficient support strength in specific weak surrounding rock sections.To address challenges including vulnerable monitoring points,significant construction interference,and humid dust environments,measures such as reinforcing protection points,optimizing workflows to reduce interference,selecting environment-resistant equipment,and enhancing calibration are adopted.A real-time monitoring system is established for dynamic analysis and early warning,ensuring data reliability and guiding construction safety.

Abstract:To study the degradation mechanism of the mechanical performance of the main girder of a prestressed concrete cable-stayed bridge under the action of vehicles and external factors,the cable-stays are equivalent to elastic supports.Using an equivalent three-span continuous beam as the basic structure,the analytical expressions for the degradation laws of cable force,bending moment,and deflection of the main girder after damage are derived.The research results indicate that after damage to the main girder,the cable force near the damaged area of the main girder increases;the changes in bending moment and deflection of the main girder primarily occur in the damaged span.Case studies validate the effectiveness of the theoretical calculation results on the degradation of the mechanical performance of the prestressed concrete cable-stayed bridge after damage to the main girder,which can be used for assessing the mechanical performance of the main girder after damage.

Abstract:To investigate the road performance of high modulus asphalt mixtures(HMAM)in long-life pavement applications,high boiling point petroleum is incorporated into base asphalt to prepare high modulus asphalt binder(HMAB).Penetration,softening point,brittleness point,and dynamic modulus tests are conducted to evaluate HMAB's hardness,high-temperature stability,low-temperature crack resistance,and dynamic load response characteristics,demonstrating its modulus enhancement and performance advantages over conventional binders.Furthermore,dynamic modulus,moisture susceptibility,rutting resistance,and fatigue tests are performed on HMAM to assess its structural stiffness,moisture resistance,high-temperature rutting resistance,and durability,confirming its suitability for long-life pavement compared to conventional mixtures.Results indicate that HMAB exhibits significantly higher stiffness than conventional asphalt while maintaining comparable low-temperature performance.Under high-temperature conditions,HMAM demonstrates a 50%higher dynamic modulus,approximately 10%improvement in moisture resistance,twice the resistance to permanent deformation,and 5～10 times greater fatigue cracking resistance compared to conventional mixtures.

Abstract:To enhance highway bus traffic safety and reduce accident rates,data from 2,320 samples are collected,including bus accident frequency,traffic volume,road characteristics,weather conditions,and holiday proportions,from three highways in eastern China.Accounting for accident heterogeneity,Poisson-lognormal(PLN),random parameters Poisson-lognormal(RP-PLN),and random effects Poisson-lognormal(RE-PLN)models are established.The Bayesian method and Markov chain Monte Carlo simulation estimate the posterior distribution of model parameters.The modeling results quantitatively assess the impact of various factors on highway bus accident frequency.Findings indicate that the RP-PLN model exhibits superior goodness-of-fit compared to the PLN and RE-PLN models.Road segment length,traffic volume,and holiday proportion show positive correlations with accident frequency,while temperature,relative humidity,and visibility demonstrate negative correlations.Holding other factors constant,a 1%increase in road segment length and traffic volume increases accident frequency by 0.90%and 0.62%,respectively.A one-unit increase in holiday proportion increases accident frequency by 8.30%.Conversely,a one-unit increase in temperature,relative humidity,and visibility reduces accident frequency by 5.72%,8.82%,and 6.55%,respectively.

Abstract:In order to analyze the extent of the influence of urban land use and road network morphology on interregional highway traffic accidents,33 towns along five highways(G503,G302,G334,G203,S514)in a northern city are selected as research subjects.The topology characteristic parameters are obtained by modeling the urban road network,and the intensity of land use and the degree of mixed land use are calculated using points of interest(POI).The random forest model is employed to analyze the influence of independent variables on interregional highway traffic accidents,and the correlation between independent variables and interregional highway traffic accidents is analyzed using negative binomial regression.The results indicate that the feature importances for the number of POIs,betweenness centrality of the interregional highways,degree of the interregional highways,number of urban nodes,and degree of mixed land use in the random forest model are 0.62,0.14,0.11,0.07,and 0.06,respectively.The number of POIs has the greatest influence on interregional highway traffic accidents,while betweenness centrality and the number of nodes of the interregional highways have some influence.The number of urban nodes and the degree of mixed land use have weaker influence on interregional highway traffic accidents.In the negative binomial regression method,the betweenness centrality of the interregional highways and the number of POIs are significantly and positively associated with interregional highway traffic accidents,while the number of urban nodes,degree of the interregional highways,and degree of mixed land use are not significantly correlated.The conclusions of the random forest model are close to those of the negative binomial regression analysis.The random forest model adapts well to the non-additive and non-linear characteristics of the independent variables and is suitable in analyzing the causes of traffic accidents.Controlling urban scale and reasonably planning urban road networks are of great significance in reducing the risk of interregional highway traffic accidents and improving traffic safety.