English to Chinese Social Sciences Social Science, Sociology, Ethics, etc. public bathrooms

The question usually focuses on demand, which can be difficult to determine when the facilities are outdoors. The National Park Service {cost-efficiently determines} park restroom demand by 1) recording complaints and other feedback from park users about the lack of toilet facilities in a location, and 2) placing portable sanitation units (PSUs) in that location and monitoring their use based on the volume of waste removed.