How is carbon monoxide poisoning not a problem in parking garages (especially the underground ones)?
they’re ventilated, and most new catalytic converters don’t generate nearly as much CO for it to be an issue
also, most cars are gonna be parked. and off.
Most building codes require if a parking garage is not “open” (“open” is a legal term defined by law usually based on amount of open space, volume, etc.) they must be mechanically vented.
If you are in a underground garage and listen closely you can likely hear the exhaust fan running.
They have ventilation systems, most importantly.
Second, most people are not spending a lot of time in there. They drive the car in, they drive the car out.