Research On The Vulnerability Of Urban Public Transportation System Under Waterlogging

Urban public transportation system,which helps solve problems such as traffic congestion,environmental pollution,and accessibility inequality caused by the urbanization,is one of the most important infrastructures in citizens’ daily lives.However,waterlogging which gets more and more frequently has greatly affected the operation of urban public transportation system.Hence,it is essential to study the vulnerability of urban public transportation system under waterlogging for better protecting and planning of urban public transportation system.This thesis proposes a framework to study the vulnerability of urban public transportation system under waterlogging,which includes 4 steps.First,this thesis establishes a two-layer raster-based model for urban public transportation system,including raster-based models for bus system,subway system,and the bus-subway complementary relationship;and the raster-based travel time and primary-based based travel time is compared to verify the feasibility of the raster-based model.Second,this thesis combines the rainfall,inundation,and drainage to establish a raster-based waterlogging model,and generates 5 waterlogging scenarios caused by rainfalls with different return periods.Third,taking accessibility as the system performance index,this thesis proposes definitions and calculation methods of the worst-case-based vulnerability and the recovery-based vulnerability for urban public transportation system.Fourth,this thesis analyzes the accessibility and the vulnerability of urban public transportation system under different waterlogging scenarios;calculates the best raster-based protect strategies based on two vulnerability metrics;and then analyzes the accessibility and the vulnerability of urban public transportation system considering the deceleration effect caused by waterlogging.This thesis applies the proposed framework to the public transportation system of Wuhan,the main results are as follows:(1)The correlation coefficient of the travel time between bus stations calculated by the raster-based model and primary-based model is greater than 0.98,and the average deviation is less than 5 minutes,indicating that it is feasible to use raster-based model to calculate the accessibility of urban public transportation system.(2)Wuhan bus system is greatly affected by waterlogging,with the accessibility reducing up to 76%;besides,the bus-subway complementary relationship can significantly improve the accessibility and connectivity of Wuhan bus system under waterlogging.(3)The best protect area to reduce the vulnerability of Wuhan public transportation system is usually located in Hongshan District,indicating that the waterlogging prevention capacity of this area needs to be strengthened.(4)Compared with the line cancel,the deceleration caused by waterlogging have minor influence on the accessibility and vulnerability of Wuhan public transportation system,indicating that it is feasible to only consider line cancel when calculation the accessibility and vulnerability of urban public transportation system under waterlogging.These results can provide guidance for the protection and planning of Wuhan public transportation system.And the proposed framework can be applied in other cities.