The shared resource argument is a good one, but why are only taxis limited? There are other approaches (for example, congestion charging as used in London) whi

The shared resource argument is a good one, but why are only taxis limited? There are other approaches (for example, congestion charging as used in London) which can be more closely tailored to whatever outcome the regulator is trying to improve, be it reducing overall traffic volumes, reducing pollution, or restricting certain kinds of traffic at certain times of day. A congestion charge scheme akin to London would be a better approach, as it can be more easily tweaked for whatever goals you're trying to achieve (overall reduction in traffic, prioritizing environmentally-friendly vehicles, keeping goods vehicles out of the city during rush out, etc).