So how much did it really help to design a city to facilitate this when they still have vast pollution issues from cars?
Can you say the old cities of Europe were designed to facilitate biking? Nor were they designed for cars, as cities like Los Angeles were. Most of them weren't "designed" for anything but the glory of the monarchy.
If people are biking in Europe, it's most likely despite the city's design, not because of it.
Here in the US, we had cities that were so choked with smog that it caused respiratory ailments. It took the EPA a couple of decades to fix that, much in the same way they cleaned up the Great Lakes. I'm not sure one fix like "odd/even license plate days" are going to fix Europe's problems quickly.