Of course there's never enough parking! If you gave everyone free pizza, would there be enough pizza? -- One of the great quotes from the book Suburban Nation: The Rise of Sprawl and the Decline of the American Dream. Here's more:

To what extent is automobile use a "free good? According to Hart and Spivak, government subsidies for highways and parking alone amount to between 8 and 10 percent of our gross national product, the equivalent of a fuel tax of approximately $3.50 per gallon. If this tax were to account for "soft" costs such as pollution cleanup and emergency medical treatment, it would be as high as $9.00 per gallon. [Probably a lot more if wars for oil are included--Bob] The cost of these subsidies--approximately $5000 per car per year--is passed directly on to the American citizen in the form of increased prices for products or, more often, as income, property, and sales taxes. This means that the hidden costs of driving are paid by everyone: not just drivers, but also those too old or too poor to drive a car. And these people suffer doubly, as the very transit systems that they count on for mobility have gone out of business, unable to compete with the heavily subsidized highways.