The definition of a good indoor climate is important to the passengers’ thermal comfort in subway stations, as it will decide its energy consumption also and thus influence its sustainability. The intention is to use the results to optimize the control of the air conditioning system to provide an indoor climate that passengers will find comfortable. This book shows that outdoor air ventilation, temperature, humidity and clothing are major factors that influence passengers' thermal comfort. The current book suggests modifications that can be made for stations to provide more comfort environment for millions of passengers using this type of transportation. It also discusses and analyzes the energy impact and thermal comfort level for each modification.