A Backpropagation-Based Algorithm to Optimize Trip Assignment Probability for Long-Term High-Speed Railway Demand Forecasting in Korea

Featured Application: (1) The concept of trip assignment probability was used to simulate passenger behavior of selecting different HSR stations in a zone, unlike the existing all-or-nothing-based optimal strategy algorithm. (2) By optimizing the trip assignment probability using a backpropagation-based algorithm, the accuracy and time efficiency of long-term HSR demand forecasting were improved compared with the existing calibration process using a trial-and-error approach. (3) The estimation accuracy of the backpropagation-based algorithm was especially superior when applied to an area with multiple accessible HSR stations, such as the Seoul metropolitan area, as well as non-metropolitan areas with a single accessible HSR station. In Korea, decisions for high-speed railway (HSR) construction are made based on long-term demand forecasting. A calibration process that simulates current trip patterns is an important step in long-term demand forecasting. However, a trial-and-error approach based on iterative parameter adjustment is used for calibration, resulting in time inefficiency. In addition, the all-or-nothing-based optimal strategy algorithm (OSA) used in HSR trip assignment has limited accuracy because it assigns all trips from a zone with multiple accessible stations to only one station. Therefore, this study aimed to develop a backpropagation-based algorithm to optimize trip assignment probability from a zone to multiple accessible HSR stations. In this algorithm, the difference between the estimated volume calculated from the trip assignment probability and observed volumes was defined as loss, and the trip assignment probability was optimized by repeatedly updating in the direction of the reduced loss. The error rate of the backpropagation-based algorithm was compared with that of the OSA using KTDB data; the backpropagation-based algorithm had lower errors than the OSA for most major HSR stations. It was especially superior when applied to areas with multiple HSR stations, such as the Seoul metropolitan area. This algorithm will improve the accuracy and time efficiency of long-term HSR demand forecasting.