I've just listened to a really interesting podcast from Jon Winston's Bikescape (Episode 47, 20/10/07). It includes an interview, about 19 mins in, with Dave Snyder, Transportation Policy Director San Francisco Planning and Research and on the Board of 'Liveable City' in San Francisco. They talk about what happens when parking is unrestrained in a city. Note 'Transit' means 'Public Transport, cycling etc'.
In San Francisco a one bedroom flat costs $2,000 a month but you can park your car (if you have one) for free in many places. This is referred to as a 'market distorting subsidy'. The space occupied by cars could be occupied by accommodation and this would bring the price of accommodation down. Dave makes the point that if you do want to subsidise car use in this way then that's fine but you should not pretend it's not a subsidy. And you must recognise that if you spend public money doing this there will be less for other things like drug treatment centres etc.
Consider the supermarket in this country. Supermarkets are required by planning law to provide parking for their customers and this is generally free. But it's not really. The high value space the cars occupy isn't free. It costs money to provide and the opportunity cost is big. This cost is recouped by the prices charged for the stuff in the supermarket. OK so far. But we all pay the same prices for goods in the supermarket even if we walked there or cycled. So, when we go to the supermarket in the car we are being subsidised to do so. As a car user we are not paying the true cost of our action.
In the jargon, the true cost of using a car is 'externalised'. It is not being paid for in total by the car user. The car users are being subsidised by the non car users who use the same supermarket and pay the same supermarket prices.
On this basis, would you pay for parking at your local supermarket on the basis that what they sold would be slightly cheaper?