I've done the experiments myself. The street that I live on is a rat-run, on which drivers speed through a residential neighborhood with lots of bicyclists, kids, people walking dogs, students walking to school, and the like. The street is ridiculously wide, enough for four vehicles to squeeze by.

So I sometimes park my vehicle on the street. (I bike to work, and most other places.) That visual narrowing of the street is enough to slow them down a bit. The best day was when the people across the street had contractors in, and they parked their trucks on the street while I parked my vehicle on my side. There was still room for two vehicles to squeeze by (and the bus drivers would YOLO it through), but it felt so narrow that most people would stop for oncoming traffic, and take turns through the cataract.

Or choosing a width and windiness to achieve desired speeds, fill the reclaimed space with bike lanes and parking or bus stops or gardens or playgrounds in the widest parts