Not sure if it's still allowed in Japan, but I still recall walking through a smoking car on a bullet train on my way to my non-smoking car about 20 years ago and my god, I'm pretty sure there was zero ventilation with the whole car smoking. I had to hold my breath from one end to the other, it was so intense. I can't fathom how people could survive a whole train ride in there while also smoking themselves. I wouldn't be surprised if this is still allowed as smoking is still quite ubiquitous in Japan. They even smoked inside at work. Being from North America, it was like stepping back in time 20 years.