If you were the city planner, what would you suggest for the ventilation on the underpass?

Question

If you were the city planner, what would you suggest for the ventilation on the underpass? Would you use AHU? exhaust fan or other suggestions..

Answer 1

I would get my inspiration from nature. For example, ants know how to build nests so that the difference of air pressure(or wind speed) between two entrances (located at different heights on the soil) creates a constant flow of fresh air inside the nest, so oxygen comes in and carbon dioxide goes out automatically,  also keeping them cool (the heat and humidity inside the nest are kept constant so the eggs and larvae can grow safely). Rabbits build warrens the same way, complex network of interconnecting tunnels and chambers up to hundreds or thousands of meters in total length, and they do not get asphyxiated... even without AHUs.

Some smart architects designed buildings this way, using auto-ventilation. The terminal at Kansai International Airport in Osaka, Japan is one case, and it's a big building.

For an underpass, keep in mind its length/width/shape, volume of air inside, volume of trafic passing through (how many pedestrians, vehicles), and also legal safety measures, to calculate if (and how many, how powerful) AHUs are required. Consult a construction engineer specialized in tunnels, he knows the formulas.