In the design proposal, exhaust from the buses and the central power plant are captured and filtered through biological systems in the Park that absorb and process carbon dioxide. To reduce the energy required to cool the building, the size of the Transit Center’s footprint makes it possible to take advantage of “ground coupling” — a process that harnesses the relatively low temperature of the Earth to chill water passively. Pipes will be coiled around the foundation’s concrete pilings, circulating water deep below grade. The waterways of City Park are used to recover and treat the Tower’s and Transit Center’s greywater, allowing the water to be reused for landscape irrigation, cooling towers, and restrooms. The large scale of City Park is another benefit. What would otherwise be a five-acre roof, absorbing and radiating heat, will instead be a green, cool park, reducing the effect of San Francisco as an “urban heat island.”