Here's a question for you: How many parking spaces should a convent be legally required to provide?

If you immediately answered "zero," that's probably because you have some common sense. Parking at a convent shouldn't be a zoning question. The Mother Superior should be able to do whatever she wants. When there's a problem, the nuns will tell her.

In fact, however, that's not the way it works in most American cities. Convents usually have to have a minimum amount of parking to stay within the law. So do at least 265 other kinds of enterprises, including golf courses, zoos, sex shops, slaughterhouses, maternity hospitals and taxi stands. All of them are on a list compiled by Donald Shoup, an economics professor at UCLA, in a new book that is undoubtedly the most comprehensive study of parking ever undertaken in this country.

Shoup tells us, among other things, that the most common requirement for convents is one space for every 10 nuns in residence. That may seem a little arbitrary, but some of the others are worse. Taxi stands, for example. I've never met anybody who drove to a taxi stand, parked, and then hailed a cab. The average cabbie doesn't need parking either--he uses one vehicle, and it's on the road during business hours. And yet most cities not only require parking spaces at cab stands but also require a fixed number: one space for each employee on the largest shift, plus one for each taxi. Some zoning laws demand extra spaces for "visitors"--whoever they might be.

Where do rules like this come from? In general, they come from a document called "Parking Generation," which was first published decades ago by the Institute of Transportation Engineers and has been updated periodically since then. As Shoup puts it, local zoning officials who consult Parking Generation "act like frightened supplicants bowing before a powerful totem. ITE's stamp of authority relieves planners from the obligation to think for themselves because simple answers are right there in the book."

Unfortunately for convents, taxi stands and countless other enterprises, the answers in the ITE book make very little sense. They tend to be based on a percentage of maximum occupancy--that is, the largest number of cars ever likely to use a facility at a given moment. The manual recommends enough spaces to ensure that virtually every driver will be able to find one virtually all the time. And then cities go ahead and require those spaces as a matter of law.

Think how odd that is. If I were building a hotel, and I knew that I could fill 200 rooms on the busiest day of the year, but only 50 on an average day, I wouldn't build 200 and leave three-quarters of them empty most nights. I wouldn't open a restaurant so big I couldn't fill it up except on Valentine's Day and New Year's Eve. Neither would you. You'd just accept it as a fact of life that once in a while, somebody will have to be turned away.

It's only when it comes to parking lots that planners and local governments insist on invoking a concept as foolish as maximum capacity. And that's for a rather simple reason: When it comes to parking, nobody worries about losing money. Parking, after all, is free.

Or, rather, they think it's free. Of course, it isn't. That's the idea that Shoup sets forth in abundant detail in his book, which he calls, appropriately, "The High Cost of Free Parking." If I were to tell you a 733-page book about parking is a great read, you probably wouldn't believe me. The fact is, however, that Mr. Shoup's opus not only is lucid and convincing but also witty, erudite and highly enjoyable. It quotes Albert Einstein and Robert Frost, Lewis Carroll and Graham Greene. It is filled with quirky little details about the way ordinary people go about their lives.

Most of all, however, it is filled with animosity toward free parking. Shoup hates free parking--especially the off-street parking that developers and businesses are required to provide in order to operate. He says it degrades urban life in ways that hardly anybody bothers to think about. "Because we never see the money we spend on parking," he says, "it always seems someone else is paying for it... but by prescribing massive overdoses of parking, planners are poisoning the city."

How, exactly? Well, for one thing, parking lots eat up a huge amount of land that could be used for more productive purposes. Many shopping malls devote 60 percent of their surface land to parking spaces and only 40 percent to the buildings. For the most part, that's not because developers insisted on all that parking. It's because zoning law forced them to create it. Either way, the result is oceans of asphalt and an ugly landscape as far as the eye can see.

All the land that's paved over and reserved for cars is land that can't be used for housing--affordable or any other kind. Because parking requirements have taken so much land out of development, they force up the cost of building on whatever land remains. Rents are higher than they would otherwise need to be. What's more, the parking requirements written into zoning law make smaller, moderately priced apartments difficult to produce anywhere.

Some cities in Southern California require residential developers to provide as many as 3.25 spaces per apartment. That often leaves as practical only two kinds of projects: a massive, sprawling condo complex that meets the requirement by paving over additional acres of land, or a boutique development that makes money by selling or renting luxury units at luxury prices. A densely built project filled with compact two- and three-bedroom apartments just doesn't cost out.

Meanwhile, in the central business districts of older cities, the amount of parking keeps increasing and the number of buildings keeps declining. Buffalo and Albuquerque devote more central-city land to parking lots than to all other uses combined. For anyone who wants to come downtown, a member of the Buffalo City Council lamented a couple of years ago, "there will be lots of places to park. There just won't be a whole lot to do here."

That's one of the simple ironies of this whole depressing subject. But there's an even bigger irony: The central city districts that have done really well in recent years aren't the ones that have provided the most parking; they're the ones that have provided the least. Portland, Oregon, instead of expanding its downtown parking capacity, has spent the past 30 years restricting it. There was less parking per capita in downtown Portland in the 1990s than there was in the 1970s. And Portland, as any visitor notices at once, has one of the most successful downtowns in America.

Los Angeles and San Francisco both opened new concert halls in the 1990s. Los Angeles included a six-level garage for 2,188 cars, built at a cost of $110 million. San Francisco, on the other hand, put in no garage--for a total cost of nothing. After each concert in L.A., the patrons head straight for their cars, leaving the area around the building deserted. After concerts in San Francisco, people spill out onto the local streets, spending money in local bars, restaurants and bookstores. Some of them have to walk several blocks to their cars parked along the curb, but every block they walk adds extra life to the neighborhood.

How smart do cities have to be to learn the lessons of all this? Smarter than most of them have been so far, apparently. But as cynical as Shoup can sometimes sound, he has a few modest proposals for dealing with the disasters of parking policy.

First, he suggests, instead of making developers build off-street parking, allow them to pay a fee in lieu of each space provided. If you make the fee less than the cost of building the space, most of them will accept that deal. Some 25 American cities are actually doing this. Most of them are small towns in California, or wealthy suburbs in the east, but there are some surprises. Orlando, Florida, allows subsidies in lieu of parking. So does Chapel Hill, North Carolina. The developers get to spend more money on the actual project. And the fees go for public improvement in the area.

Then, since the amount of parking will be reduced, allow commuters to take the value of a free parking space in the office lot and trade it in for cash. They can use it on public transportation, and if they don't spend it all, they can keep what's left over. Different versions of this experiment have been tried in Denver, Dallas, Salt Lake City and San Jose.

Ultimately, though, as Shoup himself concedes, there's a more basic answer: Local governments have to rethink the whole idea of parking. Even here, there's something to report. Minneapolis and Chicago are now exempting the first 4,000 square feet of retail space in a new development from any parking requirements at all. That's a tiny step, but it's a step.

The asphalt jungle we have created will not disappear anytime soon. As Shoup says, "automobile dependency resembles addiction to smoking, and free parking is like free will take decades for cities to recover from the damage." That's a sobering thought. On the other hand, as the Chinese would probably understand, sometimes even a journey of a thousand miles has to start with a single parking space.Ironically, the central city districts that have thrived in recent years aren't the ones that have provided the most parking; they are the ones that have provided the least.