[w-m]

But the ventilation doesn't go to the void, it will just be blown into the same neighborhood. So unless it's filtered in the tunnel ventilation system, you still get the same fumes there.

[apexalpha]

But you get considerably less fumes because the traffic isn't in a constant traffic jam because of the traffic lights on the highway.

Also, the end of the tunnels are a bit more out of the town centre than the road that was dead in the middle.

[oh_sigh]

You can have ventilation stacks that at least distribute the exhaust higher into the atmosphere, or at key points where fewer people live. I don't know specifically if they do that here though.