An Algorithmic Approach to Line Construction in Existing Transit Networks
Zezhi Deng, Ruoxing Yang
TL;DR
This paper tackles the problem of adding a new transit line to an existing network without altering current infrastructure, with the objective of improving overall efficiency. It introduces a greedy Line Addition Algorithm coupled with a demand- and path-based efficiency framework that accounts for construction cost, path complexity, and transfers. Through a Washington Metro case study, the authors show that, depending on parameter choices and alignment between pathfinding and complexity weights, the new line can either enhance or degrade network efficiency. The work provides practical guidance on parameter selection and demonstrates a reproducible, open-source approach for planners to analyze the impact of new lines on large fixed networks.
Abstract
Transit networks often have existing infrastructure that cannot be modified when designing new lines for the network. This paper provides an algorithm to generate a line within a transit network without changing any existing lines or connections between stations. Additionally, a method of analyzing the efficiency of a transit line and network is provided, and used within the algorithm presented. An analysis of the effects of different parameters and objectives on the location of a new line is performed. We find that under most cases, a new line generated improves the overall efficiency of the network, while under certain circumstances, an unsuitable combination of pathfinding algorithm and efficiency evaluation method or an increase in construction and maintenance cost can cause the algorithm to create a less efficient network.