Comprehensive risk assessment of Pakistan railway network: A semi-quantitative risk matrix approach.

Pakistan Railway (PR) is vital to the country's transportation infrastructure, facilitating passenger and freight transportation. However, the growing number of accidents associated with PR has raised concerns about its overall safety. In addition, there have been limited research efforts to investigate PR accidents and their underlying causes The present study conducts a comprehensive risk assessment and safety management of PR using a semi-quantitative risk matrix approach. The study combines historical accident data and expert evaluations to assess the likelihood and consequences of different railway accident types and potential contributing factors. The descriptive statistics analysis has revealed varying degrees of severity for different types of railway accidents in Pakistan. For instance, accidents like passenger and goods train derailments and collisions at unmanned level crossings were identified as extreme and intolerable, whereas train fire accidents were categorized as high and undesirable. Moreover, accidents attributed to human error are classified as extreme and intolerable, while those caused by negligence of road users and track defects are classified as high and undesirable. The study utilized the risk matrix approach and identified critical risk areas that can help the decision-makers prioritize effective risk mitigation strategies. In light of the present study's findings, policy implications, such as investment in infrastructure to mitigate risks associated with aging or deteriorating tracks, bridges, and tunnels, and human resource development for railway personnel to improve their skills, decision-making abilities, and awareness of safety protocols, are recommended.

Optimization of Railway Mixed Goods Loading Layout considering Stability.

It is well known that stability, center-of-gravity balance, and concentrated-weight are key factors of the transportation safety. The reasonable formulation of the loading layout scheme ensures the safety of shipment based on fully utilizing the effective volume and load capacity of freight vehicles. This paper takes the railway mixed goods loading layout as the research object, considering the constraints such as goods loading center-of-gravity balance, the allowable moment of concentrated-weight, supporting and goods placement mode, and taking the maximum comprehensive utilization rates for both effective volume and load capacity of freight vehicle as the optimization objective, an optimization model of railway mixed goods balanced and anticoncentrated-weight loading layout considering stability is built. Additionally, this paper designs mixed goods classified and simple/general goods block composition methods. We improve the representation and selection of layout space, construct goods block selection algorithm based on the greedy d-step lookahead tree search and goods block evaluation function and propose a goods block placement strategy and update rules of layout space after goods block placement. An optimization algorithm of railway mixed goods balanced and anticoncentrated-weight load layout considering stability is designed. The results show that the formulated scheme not only ensures that the goods meet the full support constraints, but also the comprehensive utilization rate of the effective volume and load capacity of the vehicle is not less than 89%, and the probability of meeting the loading center-of-gravity balance and allowable moment of concentrated-weight are as high as 99% and 99.47%, respectively. The proposed method realizes the balanced and anticoncentrated-weight loading of railway mixed goods, ensures the safe, stable, and efficient goods loading, and provides decision support for the safe loading layout of railway goods.

The dynamic tradeoff between safety and efficiency in discretionary lane-changing behavior: A random parameters logit approach with heterogeneity in means and variances.

The discretionary lane-changing behavior is highly associated with crash occurrence. This paper investigates the dynamic tradeoff between safety and efficiency and influencing factors of the decision-making process for the discretionary lane-change. A random parameters logit approach with heterogeneity in means and variances is employed on a microscopic vehicle trajectory dataset. Four vehicles are analyzed as a discretionary lane-changing group, and both the distance-related and speed-related factors are taken into account to examine their dynamic effects. The modeling results indicate that (1) two distance-related variables produce significant random parameters with heterogeneity in means and variances, while there is only one speed-related variable having significant result for heterogeneity in means and variances; (2) the relationship between the speed of lane-changing vehicle and the heterogeneity in mean of vehicle clearance distance between leading vehicle in current lane and lane-changing vehicle quantitatively demonstrates that when the driver decides whether to change lanes, the driver considers the tradeoff between distance (i.e., safety) and speed (i.e., efficiency) at the same time; and (3) the number of significant variables is gradually decreased during the lane-changing decision-making process. It demonstrates that the lane-changing decision is a dynamic process where drivers gradually select more critical factors and pay more attention to them.