A Review of Alignment Optimization Research for Roads, Railways and Rail Transit Lines

Roads, railways and rail transit lines play major roles in transporting passengers and freight. In the design process for such transportation infrastructures, the alignment determination greatly affects their life-cycle performances. However, due to the great complexity associated with alignment design, conventional manual work is very time-consuming and laborious, which consequently prompts the flourishing development of intelligent alignment optimization (AO). Hitherto, with considerable invested efforts, numerous remarkable AO studies have been reported. In this work, we present the first-known literature review paper in this field from the past 25 years. First, a bibliometric visualization is conducted to show the overall characteristics of AO research. Then, existing mathematical models that formulate AO problems are reviewed. Particularly, GIS-based applications for AO are also analyzed in that part. Afterward, the intelligent solution methodologies for solving AO models are discussed. Moreover, two specific research topics, i.e., concurrent optimization of railroad alignments and station locations as well as the existing alignment recreation and redesign, are provided. Finally, we propose 12 possible research extensions and directions in this realm.