Sorry, but the only thing that will change my mind is a significantly casualty different between single stairwell and dual-stairwell buildings accounting for building age, construction type, property value, and occupant demographics.

Happy to hear evidence-based arguments.

The US would certainly be a nicer place to live if there were more roads with just one lane, like many older cities and suburbs already have.

You're comparing a situation that happens all the time (opposing traffic) with one that happens extremely rarely (blocked stairwell in a fire). If anything, you're strengthening my point.

We should design for situations to a level that is appopriate given their frequency and severity. Show me evidence that MANDATING the extra stairwell justifies the huge increase in national housing cost, and I'll concede.

Why would you need two lanes in each direction, except perhaps on a highway..? I agree, such a waste of space.