The design and planning of railway alignments is the dominant task in railway construction. However, it is difficult to achieve self-learning and learning from human experience with manual as well as automated design methods. Also, many existing approaches require predefined numbers of horizontal points of intersection or vertical points of intersection as input. To address these issues, this study employs deep reinforcement learning (DRL) to optimize mountainous railway alignments with the goal of minimizing construction costs. First, in the DRL model, the state of the railway alignment optimization environment is determined, and the action and reward function of the optimization agent are defined along with the corresponding alignment constraints. Second, we integrate a recent DRL algorithm called the deep deterministic policy gradient with optional human experience to obtain the final optimized railway alignment, and the influence of human experience is demonstrated through a sensitivity analysis. Finally, this methodology is applied to a real-world case study in a mountainous region, and the results verify that the DRL approach used here can automatically explore and optimize the railway alignment, decreasing the construction cost by 17.65% and 7.98%, compared with the manual alignment and with the results of a method based on the distance transform, respectively, while satisfying various alignment constraints.
INTRODUCTIONThe planning and design of railway alignments is not only the foundation of railway construction but also an extensive and systematic task. The direction of a railway alignment directly affects the difficulty, cost, and safety of the railway construction and operation. Therefore, the final railway alignment design should not only consider a series of natural factors such as geology and topography in the © 2021 Computer-Aided Civil and Infrastructure Engineering railway area but also satisfy other constraints, including those regarding the existing railway, historical sites, and environmental protection zones in the target area. Overall, pathfinding for a railway alignment is an optimization and decision-making problem involving many restrictive factors (Li et al., 2013). Traditional railway path planning is performed manually. Based on work experience and accumulated knowledge, designers analyze, evaluate, and compare multiple Comput Aided Civ Inf. 2022;37:73-92.wileyonlinelibrary.com/journal/mice ing requirements, thus ensuring that the horizontal alignment satisfies the constraints in the horizontal plane. In this study, we set 𝑅 𝑖 as a fixed value, which should exceed the minimum allowed value of 600 m (specified in Table 1), to fit the horizontal circular curve.