I don't think there's a good one-size-fits-all rule. A 3 bedroom unit could be 3 couples living together and splitting the rent, or it could be 1 family, or it could just be 1 person who wants an office and a gym. The rule should probably be "1 space for car owned", like when you go to buy a car, you have to prove that you have a place to park it.
Just restrict who can park on the street. Then if people want to park a car, they'll need a residence with a space, and if there's demand for residences with parking spaces, developers will build them, minimums or not. The issue with minimums is that they require building spaces above and beyond demand, but markets should do just fine at making sure demand is met, as long as there are barriers to externalizing it.
In Japan you have to vouch that you have a parking space for your car. I think a similar rule would work for the states. However, it will cause a huge tension between the parking spot haves and parking spot have nots, without adequate equality will be seen (rightfully so) as a move to limit cars among those who can't afford parking spots for them.
For better or worse, the USA has basically made a contract with its people that "you have the right to a car, and because of that, we will provide really sucky public transit." That contract has to change before we start aggressively taking cars out of the system.
You don't have to "vouch" that you have a parking space, you have to prove it. The police will actually come to your home and measure your parking space to make sure it's big enough for the model of car you want to buy.
I can't imagine Americans submitting to a law like this.
> if there's demand for residences with parking spaces, developers will build them
That's somewhat optimistic. In the absence of rules, developers will maximize their profit above all else. Apartment units are far more profitable than parking, so they'll just build the maximum units with no parking.
I lived in such a neighborhood once. Result is 50 unit buildings with 4 parking spots. And the result of that? People driving around the blocks for hours looking for parking, fights breaking out over parking, cars constantly vandalized for taking over "their" spot. It was not fun.
I mean, typically laws do not substitute for the creative process of designing and marketing buildings. What color should the walls be? What kind of kitchen faucet should you have? What should the countertops be made out of? What flooring surface will you use? There is no reason that "how many parking spaces should we build" be the 1 question that the government answers for you. Make an educated guess. If you're wrong and build too many, you leave money on the table. If you build too few, then people will buy some other unit with more parking.
> What color should the walls be? What kind of kitchen faucet should you have? What should the countertops be made out of? What flooring surface will you use?
All of these can very easily be changed by future buyers if they prefer something different.
But if the developers builds a 50 unit apartment building with just 4 parking spots, that building is now there for many generations and there is no practical way to change that decision.
