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The urban expressway system serves as a key role in the roadway transportation system. It provides an efficient and comfortable approach for long-distance travel within the city. However, the safety status of the urban expressways is becoming a critical issue as the high-frequent traffic crashes have severely influenced the traffic operations. Among the safety influencing factors, including traffic operational parameters (such as traffic speed and volume), geometric features and traffic participants' characteristics (such as vehicle roadway usage patterns), the traffic operational parameters and geometric features have been widely investigated. However, the impacts of traffic participants' characteristics on traffic safety have never been examined. This unprecedented study aims to link vehicles' roadway usage patterns with traffic safety through crash frequency analyses. First, the roadway usage patterns were identified using Latent Class Cluster Analysis (LCCA) based on their traveling rates. Then, the hourly-based crash frequency analysis data were formulated with traffic operational parameters, geometric features and crash data. Finally, crash frequency analysis models were developed to unveil the relationships between the crash occurrence and their influencing factors. The modeling results showed that the Random Effects Hurdle Negative Binomial Model (REHNBM) provided better goodness-of-fit. And it concluded that higher proportions of vehicles with low-level roadway usage pattern would substantially enhance the possibility of crash occurrence; while the proportions of vehicles with the medium-high-level roadway usage pattern had negative impacts on crash occurrence probability. Finally, safety improvement recommendations and strategies based on the modeling results were put forward. [ABSTRACT FROM AUTHOR]

The urban expressway system serves as a key role in the roadway transportation system. It provides an efficient and comfortable approach for long-distance travel within the city. However, the safety status of the urban expressways is becoming a critical issue as the high-frequent traffic crashes have severely influenced the traffic operations. Among the safety influencing factors, including traffic operational parameters (such as traffic speed and volume), geometric features and traffic participants' characteristics (such as vehicle roadway usage patterns), the traffic operational parameters and geometric features have been widely investigated. However, the impacts of traffic participants' characteristics on traffic safety have never been examined. This unprecedented study aims to link vehicles' roadway usage patterns with traffic safety through crash frequency analyses. First, the roadway usage patterns were identified using Latent Class Cluster Analysis (LCCA) based on their traveling rates. Then, the hourly-based crash frequency analysis data were formulated with traffic operational parameters, geometric features and crash data. Finally, crash frequency analysis models were developed to unveil the relationships between the crash occurrence and their influencing factors. The modeling results showed that the Random Effects Hurdle Negative Binomial Model (REHNBM) provided better goodness-of-fit. And it concluded that higher proportions of vehicles with low-level roadway usage pattern would substantially enhance the possibility of crash occurrence; while the proportions of vehicles with the medium-high-level roadway usage pattern had negative impacts on crash occurrence probability. Finally, safety improvement recommendations and strategies based on the modeling results were put forward. [ABSTRACT FROM AUTHOR]

• Collaborative gas drainage technology of high and low level roadways was proposed. • The technical parameters of HLLR were optimized via numerical simulation. • The technology was applied and effectively solved the gas problems in the workface. China's coal resources are gradually being mined deeper. The gas content and emissions of deep coal seams increase significantly compared to shallow seams. In the mining of the highly-gassy coal seams, strengthening gas drainage in the goaf and fissure zone can improve the efficiency of coal seams and reduce carbon emissions. However, the method of the borehole or high level roadway often cannot meet the demand of goaf and fracture zone gas drainage. Thus, a new technology of gas drainage in goaf and fracture zone is proposed: cooperative gas drainage via high and low level roadways. Taking the Pingshu coal mine as an example, the gas flow field model of the goaf was established. Fluent software was used to analyze and simulate different gas drainage effects of high and low level roadways under different layers and negative pressure conditions, and to optimize the process parameters of high and low level roadways. The results show that the collaborative drainage effect of high and low level roadways is much better when the horizontal and vertical distances of high level roadway are 32 m and 30 m, the horizontal distance of low level roadway is 5 m, and the negative drainage pressure of both roadways is 15 kPa. The gas concentration in the upper corner can be effectively reduced under the condition. On the basis of the optimized parameters, the collaborative gas drainage of high and low level roadways was applied and effectively solved the problems of gas accumulation and overrun in the upper corner of the working face, where the gas concentration was less than 0.45%. The paper provides a new approach for gas drainage in the highly-gassy coal seams. [ABSTRACT FROM AUTHOR]

High (low)-level roadways are effective gas control measures for coal seams with high outburst potential and low permeability. The spatial location of the low-level roadway directly determines the gas drainage efficiency and can affect the success of the whole engineering project. Currently, determining the location of a low-level roadway is based mostly on empirical engineering analogies and lacks relevant theoretical support. In this work, based on the Ji-15-24080 engineering project at the No. 10 Coal Mine of Pingdingshan Tian’an Coal Industry Co., Ltd., a numerical model for the location of a low-level roadway was established using ANSYS numerical software to analyze the stress distribution in the rock surrounding the conveyor roadway for the mining face and assess the permeability-enhancing effect of the low-level roadway when it is placed at different locations. A location directly beneath the conveyor roadway was found to provide a good location for a low-level shield roadway. In addition, a quantitative distance between the conveyor roadway and the low-level roadway can also be determined. These optimization results were then directly applied in the field. Relevant industrial field tests were conducted to determine fracture development, gas pressure and stability of the surrounding rock. The field test results confirm that the proposed location for a low-level shield roadway is reasonable. We recommend that when the low-level shield roadway is placed directly beneath a conveyor roadway, it should be within 50 m of the working face, and an effective support structure should be employed to support the rock surrounding the conveyor roadway to ensure the stability of the rock. We further recommend that, in the area in front of the working face, particularly within 25 m of the working face, densely distributed gas drainage boreholes should be drilled to drain gas from the coal seam to reduce the gas pressure and lower the outburst risk. The results of this work will provide guidance for similar engineering projects to determine the location of a low-level roadway and to ensure gas control. [ABSTRACT FROM AUTHOR]