| Transportation infrastructure is fundamental for a region's development.Freeways can shorten the temporal and spatial distance between regions,strengthen the economic and cultural communication.Meanwhile,they are playing a driving and safeguarding role for social development.Since its reform and opening,China has made great achievements in freeway construction and completed the main line construction of five-vertical and seven-horizontal national freeway network.With its total mileage of freeways over 140,000 km,China is ranking the first place in the world in terms of total size.However,the rapid development of freeway construction in the short term has brought about huge pressure on the ecological environment,causing many of negatively environmental risks.These risks are mainly concerned with environmental pollution emergencies resulted from hazardous chemical transportation accidents during freeway operation.The huge leakage of hazardous chemicals will severely endanger the public life security,destroying the ecological environment,and further influence the social stability with enormous economic loss.China has made great progress in the control and management of environmental risks during freeway operation;however,its vast territory and differentiation of freeways have led to its pool understanding of relative environmental risks,accompanied by the single and ineffective methods of risk control and management.For this purpose,this paper proposes to take the environmental risks of freeway operation in China as the research object and proceeds from the representation mode of environmental risk characteristics and the formulation of control strategy,to study the applicability of risk control and management technologies and select the strategies,of great theoretical and practical values.First,LDA topic model is applied to identify the control and management measures for environmental risks from 191 freeway construction projects,and a model of high environmental risks is constructed based on literature review and Delphi method.The study shows that China's freeways mainly take 21 measures for the control and management of environmental risks at the stage of operation,which cover four dimensions,e.g.elimination,preparation,response and recovery;and the environmental risk factors of freeway operation are classified into three aspects,e.g.project factors,Party A's factors and environmental factors;and project factors are more likely to attract attention.Second,an assessment indicator system and measurement model for freeway environmental risk are constructed;entropy weight method is applied to calculate the composite index of freeway environmental risks constructed during the period between2014 and 2020.By virtue of the cluster analysis on freeway environmental risks based on K-means,the current situation of China's freeways in terms of environmental risks is disclosed.The results indicate that China's freeways are clustered into three categories in terms of risk characteristics;the proportion of freeways with a low level of environmental risks is gradually decreasing,with those of freeways with a relatively high and high level of environmental risks gradually increasing.Third,the control and management level of environmental risks of China's freeways during operation is measured;text mining and minimum spanning tree model are adopted to construct the control and management measure network for freeway environmental risks and to identify the importance of various nodes in the network and the usage pattern of various measures.G1 method is used to empower the control and management measures of freeway environmental risks;and the validity indexes of control and management for freeway environmental risks are scored based on TOPSIS,to obtain the implementation effect.The levels of control and management measure,as well as the variable coefficient and contribution ratio behind the control and management for freeway environmental risks in various regions in China are assessed based on the existing data,to obtain the main causes for the regional differentiation for the control and management levels of freeway environmental risks.Finally,the dimensions of the control and management measures for environmental risks are studied to obtain the common factors for five categories of control and management measures,including road safety assurance system,special vehicle driving control and management system,resource guarantee system,emergency command and dispatch system and emergency management implementation system.Multiple regression is applied to get the numerical relationship between the metric data of environmental risks and their validity scores of control and management measures,to provide the quantitative criteria for the applicability of control and management measures under different circumstances of environmental risks.Particle Swarm Optimization is used to simulate the decision-making process and to obtain the combination of control and management measures with the optimum applicability under the circumstances of different environmental risk characteristics based on multiple purposes.By following the idea of “identifying the control and management measures and risk factors?risk measurement?assessment of control and management level?strategy formulation of control and management”,this thesis takes the environmental risks of China's freeways as the research object;comprehensively applies the empirical and normative research,to study the key issues including the influential factors of such risks,control and management measures,measurement method,control and management level and strategies.This thesis contributes to the relevant knowledge with systematic research;enriches the theories of environmental risk management from the perspectives of environmental risk identification,construction of control and management measures,assessment of measure implementation effect,and regional differentiation of risk control and management,to provide the theoretical foundation and practical guidance for the management practice of environment risks of China's freeways. |
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