捷運運輸系統能源效率與碳排放效率之研究：以台北捷運系統為例

Study on Analyzing the Efficiencies of Energy and Carbon Emissions for the Metro Transportation System: An Example of Taipei Metro System

捷運系統具備低汙染、準點率高、班次密集特性，常被視為綠色運輸一環。然而實務上，捷運系統服務過程高度依賴電力能源使用，持續產生碳排放。本文以方向性距離函數（Directional Distance Function, DDF）概念，發展二階段混合網路DDF模型，以臺北捷運系統為例進行實證分析。透過蒐集2005至2022年之投入與產出變數月資料，衡量環境、用電量及碳排放效率課題。實證分析顯示，透過二階段混合網路DDF模型分析顯示，台北捷運系統之環境效率平均數為0.9916，全系統、生產與服務階段之用電量效率均相當接近效率前緣。營運者欲提升環境效率可優先著手改善車站碳排放效率，每季平均可減少碳排放4.96%。混合網路DDF模式除提供營運者獲取整體環境效率、生產效率及服務效能等相關評比資訊，亦能提供中運量、高運量系統與車站之能源與碳排放效率資訊，供業者作為未來發展節能減碳策略之參考。

The mass rapid transit (MRT) or metro system, known for its low pollution, high punctuality, and frequent service, plays a vital role in green transportation. However, in practice, the metro system heavily relies on electric energy during passenger transport and station operations, which results in carbon emissions and environmental challenges. This paper develops two models, a two-stage mixed network Directional Distance Function (DDF) model and a traditional DDF model, to measure environmental, energy, and carbon efficiencies. The study evaluates these efficiencies using time series data from the Taipei MRT from 2005 to 2022. The empirical analysis shows that, using the mixed network DDF model, the average environmental efficiency is 0.9916. The average carbon emission efficiency values are 0.9599, 0.9700, and 0.9504 for the entire system, production, and service stages, respectively. This means that carbon emission efficiency does not yet reach the efficiency frontier, primarily due to lower efficiency in the station system. To improve environmental efficiency, operators should prioritize enhancing carbon emission efficiency during service processes, which could lead to an average carbon reduction of approximately 4.96% per quarter. Furthermore, the traditional DDF model yields efficiency values of 0.9895, 0.9860, and 0.9830 for environmental, electricity, and carbon emissions, respectively. These findings indicate that these efficiency values still fall short of the efficiency frontier. The empirical analysis demonstrates that the proposed mixed network DDF model provides operators with valuable insights into overall environmental efficiency, production efficiency, and service performance. It also offers energy and carbon emission efficiency data for medium- and high-capacity systems and stations, which can assist operators in implementing effective ''energysaving and carbon-reduction'' measures.