It's not tragedy of the commons, it's path dependence. If you don't have excellent mass transit then you need parking, so you build parking. Then if you have parking everybody drives and nobody is willing to invest in mass transit, so you continue to need parking.
Now, we mostly see the demand for parking at zero [#] marginal cost to the parker, not the demand for parking at its true cost---because the costs are shared by society.
The short term demand for parking is relatively inelastic---so right after introducing pervasive charging for curbside parking and dropping minimum parking requirements for new developments, we will see roughly the same number of cars parked. (That's where your dependency comes in.)
In the longer term, demand for parking is more elastic. (One can see a similar relationship between oil price and demand for gas guzzling cars: inelastic / path dependent in the short run. More elastic with enough time.)
This holds even without public transport at all. Public transport is just one of the things that can serve as an (imperfect) substitute for private car rides. There are other ones, like car sharing, choosing job/home combinations that are closer to each other, telecommuting, home delivery of groceries, buying groceries in bulk, etc.
(To take one example right now, people already prefer to work closer to home, and make trade-offs all the time when considering a home or a job. The point of indifference between eg home price/salary and commute length will shift. Full disclosure: I hate commuting myself and have decided to fork out the money to live very close to the office.)
All the people in the market are probably much cleverer than me in coming up with substitutes. The price mechanism can guide them.
Some of these substitutes can and are provided by the private market. Public transport is generally not. Though eg Britain has privatised train companies.
Add in as another complication that without careful regulation, lots of public transport options are natural monopolies. One attempt to blunt this effect is by careful separation: eg run the rail network as a heavily regulated, public utility and make private companies bid for the right to run trains on it and for slots at the stations etc. And be very careful to specify that apart from meeting some minimum standards, the height of the bid alone determines the winner of the auction---politicians like beauty contests, because it gives them power to meddle.
Since I'm already on a tangent: the American freight train market and its history are another interesting piece to learn from. (It's doing pretty well, mostly because they don't have many passenger trains clogging up the network like in Europe, and the new regulatory environment of the Staggers Rail Act (https://en.wikipedia.org/wiki/Staggers_Rail_Act) seems to have worked out reasonably well. (They called it `deregulation', but that almost never happens---it's just a different form of regulation.)
[#] Zero in terms of dollars plus the effort and hassle of congestion and cruising for parking.
> All the people in the market are probably much cleverer than me in coming up with substitutes. The price mechanism can guide them.
I'm not sure you're going to like the market price of parking. If a parking space is 25% of the size of a $3000/month apartment then the market price of a parking space should be something like $1/hour, which isn't that high. And which puts it right in the hard spot where people subsidizing the price down to zero may actually make sense.
If all you care about is maximizing the revenue from parking spaces then you can set a price like that, but having a price at all discourages people from using parking spaces that you've already paid to construct whether you use them or not. And if you don't use them then the local shops lose customer traffic. So the local shop owner does the math and says hey, if there was free parking here I would get an extra $20,000 profit from more customer traffic, so I should go lobby the city to have free parking even if it means my taxes will be $10,000 higher.
Then their customers realize that if parking was paid for through taxes rather than at the meter the local businesses would be paying part of it instead of the customers paying all of it, so they would be paying less, and paying at the meter is more stressful than paying via taxes anyway.
Then the government realizes that to get the money from taxes they only have to put a slightly higher tax rate on the tax forms but to get it from parking they need meters and credit card processing computers and customer service and parking wardens and dispute resolution systems and the whole works.
So the vote comes up and 90% of everybody votes for free parking because the lack of free parking would collectively cost them more in money and grief than it costs to provide free parking.
The way out of this is to make the alternative to cars (or parking) more attractive, without making cars less attractive. Because people are going to fight you and win if you try to make cars less attractive without immediately replacing them with something which is at least as good.
Already existing parking (especially curbside parking) should be priced to reach approximately 85% occupancy. Less, and you are leaving too many spaces empty, higher and people have to cruise for a while before they find a spot.
That pricing will not discourage too many people directly---because you price it exactly at a point where not too many people are discouraged. (That point might have to be adjusted over time.)
Like a congestion charge, you shift from people bidding with their willingness to sit in traffic and endure queues, to people bidding with their chequebook. (Interestingly, your mix of parkers would shift towards more people who value their time more than their money. Affluent customers are good customers!)
Congestion charges worked out well for Singapore and London.
Politically, it's a good idea to hand out the fees from parking at the same level as the people who can decide about it. So if local opposition could derail the scheme, you have to hand out the proceeds very locally. Otherwise you get the political dynamics you describe.
Charging for parking is relatively easy and does not require high-tech. For example Singapore uses a scheme (amongst others) where you buy a bunch of perforated cards. When you want to park, you take a card and push out the appropriate chads to indicate the date and time of day and display the card in your car's window. Each card is valid for an half-hour slot. You can punch out multiple cards with consecutive slots. Each card can only be used once (obviously).
(If you want a crud variable pricing, you can require people to display multiple simultaneous cards for peak hours.)
I have also seen a system where you send a premium SMS with your licence plate number to pay.
> That pricing will not discourage too many people directly---because you price it exactly at a point where not too many people are discouraged.
Except that you're admitting to discouraging 15% of the customers. If there isn't enough parking for everyone then the shops much prefer people to be cruising around so that as soon as a space opens up there is someone to take it, rather than not showing up in the first place because they can't afford parking.
> (Interestingly, your mix of parkers would shift towards more people who value their time more than their money. Affluent customers are good customers!)
You can't actually make more money strictly by losing profitable customers, even if the customers you lose are below average customers.
> Like a congestion charge
It is like a congestion charge, which have exactly the same problems.
> Congestion charges worked out well for Singapore and London.
They keep poor people off the roads so rich people can use them, anyway.
> Charging for parking is relatively easy and does not require high-tech.
People don't use the high-tech stuff because it's harder. Either way you need something vs. the alternative where you don't need anything.
> Politically, it's a good idea to hand out the fees from parking at the same level as the people who can decide about it. So if local opposition could derail the scheme, you have to hand out the proceeds very locally. Otherwise you get the political dynamics you describe.
The problem is there are no "proceeds" -- the money is going to come from the local residents whether it's parking fees or taxes. The only way you can save anything is to have fewer parking spaces, which nobody is going to allow until after there is already a better alternative in place.
