Sometimes it doesn't even require sacrificing a lane, because many North American cities have lanes that are wildly larger than necessary or even appropriate given the posted speed limits. The lanes can simply be narrowed, and then this also causes the drivers to naturally drive at safer speeds, reducing traffic accidents, speeding tickets, and the unplanned delays that those both cause.
People are already stupid, put them in a car and their brains start leaking out of their ears.
Street space really is zero-sum, though more people in bikes and out of cars free’s up so much infrastructure that it can make less space work even better for cars- I’m sure urban designers are aware of this.
The major issue I presume that is faced in urban design is how to handle people coming from far away, the regional hub/spoke design (with train stations around a radial that have good parking allowing train access into the city) is not something actively pursued by advanced economies for some (presumably good) reason.
This is also why suburbs and rural areas are a better fit for cars. Space is much more available and you can afford to be wasteful with it.
> though more people in bikes and out of cars free’s up so much infrastructure that it can make less space work even better for cars
Yes, you've reiterated my point...