<p>This study examines the variations in noise levels across various subway lines in Singapore and three other cities, and provides a detailed overview of the trends and factors influencing subway noise. Most of the equivalent sound pressure level (<i>L</i>_eq) in typical subway cabins across the Singapore subway lines are below 85 dBA, with some notable exceptions. These variations in noise levels are influenced by several factors, including rolling stock structure, track conditions and environmental and aerodynamic factors. The spectrogram analysis indicates that the cabin noise is mostly concentrated below the frequency of 1,000 Hz. This study also analyzes cabin noise in subway systems in Suzhou, Seoul, and Tokyo to allow for broader comparisons. It studies the impact of factors such as stock materials, track conditions including the quality of the rails, the presence of curves or irregularities, and maintenance frequency on cabin noise.</p>