In urban areas isn’t the speed limit determined by the need to deal with pedestrians and other traffic? If your hypothetical tracked buses are going to go fast

In urban areas isn’t the speed limit determined by the need to deal with pedestrians and other traffic? If your hypothetical tracked buses are going to go faster than regular buses and cars there will need to be some sort of isolation of them, such as elevated tracks or underground tracks. That raises the cost significantly. You probably will only be able to afford this on a few routes that are heavily travelled and that are expected to remain heavily travelled for decades. That will probable leave a lot of your city far enough from a tracked buses stop that many won’t be within reasonable walking distance so you are still going to need some form of public transit, such as regular buses.