Which European country has a city with nearly 10M people on 300km2?

America is exceptional - in the literal sense, it's an exception compared to organically grown cities that existed for hundreds of years. It doesn't mean it's better, it's just very different and so naturally the solutions are going to be very different too.

> Which European country has a city with nearly 10M people on 300km2?

I have no idea, can you share specifically why you think autoluw only works for certain levels of population per square kilometer? To the point that the lessons couldn't be adapted and would have to be "very different?"

Much more people on that extremely small area actually need to drive - because they have reduced mobility, because they are carrying a lot of stuff, goods, materials or tools... Reducing NYC to one lane would stop all life in the city. You can drive through Amsterdam too in these cases - it works because incomparably less people need to.

There's also the problem of mass transit - you can't simply have enough bus/tram lines to cover people's needs if you have so many people who need to go everywhere around the city at one place. You'd have to build an incredibly number of subway lines like Chinese cities have, which is a huge investment.