Time-varied accessibility and vulnerability analysis of integrated metro and high-speed rail systems

Intra-city metro rail systems together with the inter-city high-speed rail system can provide very punctual transportation services for those trips with origins and destinations both served by metro stations. The travel time by metro and the transfer time between metro and high-speed rail stations averagely accounts for 26.5% of the shortest travel time of a typical trip in China. This paper considers these two types of rail systems as a whole, called integrated metro and high-speed rail systems. Different operation frequencies of these two types of rail systems make the accessibility via an integrated rail system time-varied, not only depending on the travel time, but also depending on the departure time from the origin station. In this context, this paper proposes three types of accessibility metrics: (a) the travel time based accessibility, which provides the minimum travel time from one city's metro station i departed at a given time to another city's metro station j; (b) the best departure based accessibility, which quantifies the length of the periods during which the departure time makes the travel time acceptable; (c) the round trip based accessibility, which measures the maximum time duration that a passenger can stay at the destination station for a round trip in a typical day. Based on these accessibility metrics, this paper also investigates the vulnerability of the integrated rail system in China under single high-speed train station failure and two real severe weather events. The findings provide insightful suggestions to plan the two types of rail systems as a whole.