I think you're overselling Leiden as an example of this here, isn't traffic blocked from just one main shopping street and one other (steenstraat) made somewhat hard to access?
I'm not sure I would say the latter change, which was recent-ish, made a big difference versus just the general cleanup of the inner city (better train station, spruced up Beestenmarkt square etc).
Sure, there are still plenty of places you can drive in Leiden. I guess the point I’m trying to make is small cities in North America favour car transportation to an extreme. It is to the point where it’s physically dangerous to walk to some places because their aren’t even sidewalks and traffic travels much faster inside the cities than you’d ever see in the Netherlands.
Compared to small cities in North America, Leiden infrastructure is amazing — as is a lot of Dutch towns. It not that you have to completely block off all roads either. It’s just that everywhere there are roads for cars, there’s also equal space for bike and pedestrians and public transit is invested in much more. If you want to see a video series that compares the two look up the YouTube channel notjustbikes
I'm not sure I would say the latter change, which was recent-ish, made a big difference versus just the general cleanup of the inner city (better train station, spruced up Beestenmarkt square etc).