Oh oh oh!!!

I've been researching this issue a lot. A major factor pushing streets to be wide in the US is fire codes. For buildings 3 stories and under, there needs to be a 20' clear, unobstructed path. In addition, this street doesn't have to connect directly to the front door (though many jurisdictions require it for navigability purposese), but it has to come within 150' of all exterior walls (can be extended if sprinklers are installed). So we can get pretty close to your typical japanese city...

Until you need to build that 4th floor. The requirement not only goes up to 26', but it needs to be directly adjacent to the building, but also needs to be at least 15' away from the building. Talk about a spike in space requirements! You'd think it kinda defeats the entire purpose of building up in the first place, until you reach a certain height.