When yku say it like that. It makes more sense. It's a shame we don't have super efficient ways to convert exhaust gasses into healthier gasses. But yeah, if it's just a short tunnel, the entrance and exits would just not funnel it right. I wonder if really long tunnels would be better. Maybe being able to use the entrances with a system to input clean air and force the exhaust through vents.

And I wonder if those fire suppression systems that starve the fires of oxygen could be something that could be useful? But that'd require automated doors to seal the tunnel, and then if someone is trapped on there, the fire is the last of their issue. Unless there were refugee points that also seal, but then you've gotta make sure everyone's in them. I wonder if some form of scanner could be used to allow humans in. But then there's that thing where a fire has been starved, but then gets a sudden burst of oxygen and it becomes explosive. I forgot what it's called. I'm sure someone actually smart could brainstorm it better.