The impact of signaling system heterogeneity on urban transit capacity

Chinese urban transit are experiencing rapid growth and increasingly need of capacity to accommodate it. Capacity planning requires knowing how the mixture of signaling systems affects capacity. Different signaling systems have different operating characteristics including headway, end of movement authority and braking point. Heterogeneity of signaling systems using in a railway line usually reduces capacity. In this paper, Blocking time model was used to exposit the headway of signaling systems as well as the headway between trains which are running in different signaling systems. Simulation software Railsys was used to analyze the effect on capacity when trains are in different signaling systems sharing a line of Beijing metro. Analyzes included the effect of the continuous transmission-based signaling system (moving-block), the spot transmission-based signaling system (fixed-block) and especially their mix as well as the effect of the percentage of mixture and sequence of trains in different signaling systems. The effect of relationship between capacity and the mixture and sequence of trains was also evaluated as well. These analyses attempt to provide a better understanding of how the signaling systems affect railway capacity and a complete understanding of one factor on capacity. Furthermore, the results can help planners verify if the urban transit lines satisfy the capacity demand and adjust timetable arrangement.