This study numerically assesses the impact of a new railway on urban development and thermal comfort, specifically the Tsukuba Express (TX) railway in the Tokyo Metropolitan area, Japan. The railway was chosen because it connects high-, mid-urbanized, and suburban areas in the Tokyo Metropolitan region, Japan, allowing for a distinct evaluation of its impact on each urban area type. Consequently, four representative stations were selected: one in a high-urbanized area, two in mid-urbanized areas, and one in a suburban area. A numerical atmospheric model, the Weather Research and Forecasting (WRF), with a horizontal resolution of 250 m, was used to simulate the areas along the entire railway, including the stations. The study includes two simulation cases: before (2005) and after (2015) the construction of the TX. The impact of urbanization on surface air temperature distribution along the TX railway is initially assessed. The results indicate that the most significant temperature increase (1.7 °C) occurred in suburban stations between 2005 and 2015 at 1800 JST compared to other areas. Following the development of the TX railway in 2005, anthropogenic heat (AH) release from buildings and traffic increased rapidly by approximately 80 W/m2. The study highlights that areas experiencing significant increases in air temperature and energy consumption need careful attention and the implementation of feasible environmentally friendly measures.