Bioclimatological load due to stress arising from heat or coldness and sultriness has often been studied in urban climatology and interactions and influences on human beings are largely known. On the contrary, there is relatively little information on such load caused by stress in underground public transportation systems. Every day many people spend their time inside subway systems (stations, tunnels, entrances and exits) and trains. Thus, it is of particular importance to study and analyze the respective loads in underground systems.

A measurement program planned to study such influences and interactions was developed for the Subway of New York City in summer 1999 and winter 2000. At the beginning, the investigation aimed to determine the thermal load inside subway stations and to quantify temperature differences between the different levels of more complex stations, the air outside the subway system, and inside the trains, respectively. Measurements were made in August/September and February/March. In addition to air temperature, the infrared radiation temperature of ground surfaces, ceilings, and walls was recorded; furthermore, relative humidity was determined.

Results clearly show that passengers are exposed to high temperature stresses and often have to bear extreme short-term fluctuations of air temperature of orders of 10 to 20 K; especially the latter carry a very high load potential to passengers. However, it is not possible to obtain a comprehensive picture with respects to the bioclimatological conditions in subway stations when taking into account only air temperature. Thus, to assess these reliably the variables PMV (predicted mean vote) and PET (physiological equivalent temperature) were calculated from the measurement results. In addition to the latter, different types of clothing of the passengers were taken into account and these in turn were related to different times during the day.