On a slow afternoon back in 2005, I found myself thumbing through one of the oddest books I had ever come across. It was a 733-page treatise on parking by Donald Shoup, an economist at the University of California, Los Angeles, who had devoted much of his career to collecting every available nugget of information on the subject. What made the book so unusual wasn’t just the level of detail. It was Shoup’s palpable enthusiasm for the material and his ability to make it interesting. He quoted Albert Einstein and Robert Frost, Lewis Carroll and Graham Greene. He filled up the pages with quirky little details about the way ordinary people go about their lives.

All this detail was made to serve a fairly simple point: “Free” parking costs cities and their residents a fortune and gives us little more than traffic congestion and ugly downtowns. Abolishing all those free spaces could bring about a renewal of high-quality urban life. Despite his verbosity, Shoup made his main point concisely and rather convincingly. Intrigued as I was, however, I dismissed him as an erudite eccentric certain to be branded as a crackpot by the pragmatic engineers and politicians who design and govern American cities.

I was quite wrong about that. Eleven years after publication of The High Cost of Free Parking, you won’t find many people making jokes about it. Unlikely as it once seemed, Shoup’s ideas have taken root in cities all over the country. Urban planners who scarcely gave parking a second thought in the pre-Shoup era have come to regard it as a crucial force in determining the future of their communities.

This has happened for several reasons. One is the mountain of numbers and facts that Shoup and his allies have brought to the subject. More than 30 percent of the area in many downtown commercial cores is taken up by parked cars. In many places, there are four times as many parking spaces as there are vehicles. Even so, as many as half the cars crowding center city streets at any one time are cruising for a place to park. It doesn’t make a lot of sense.

But it isn’t just Shoup’s arguments; it’s the changed economics of metropolitan America. A couple of decades ago, it didn’t seem to matter that many downtowns were full of parking lots because there wasn’t much else to do with the land. Nobody wanted to build on it. That’s why it was turned into parking lots in the first place. Nowadays, cities see all sorts of uses for that land -- as sites for apartments and condos, retail businesses, and new office buildings. Because of that, a parking lot begins to look like nothing more than a waste of space. The sooner city officials can persuade the property owners to yield in favor of development, they are convinced, the better off the city will be.

Downtown isn’t the only locus of Shoupism. As cities plan their expansion over the next few decades, many of them are talking about pedestrian-friendly neighborhoods and transit-oriented development far beyond the central core. The question of what to do about parking turns out to be fundamental to the question of how they can bring their planning goals into fruition.

Seattle is a good example. Later this year, residents of the metropolitan area will vote on a massive 25-year plan that would create a transit system of 108 miles and build 39 stations. Not too long ago, the question of how much parking to build at the stations would have been a minor technicality. Now it’s seen as perhaps the most important issue. The current plan is to have as many as 18,000 new parking spaces next door to the stations. The most intense transit advocates, and some professional planners, insist that’s a mistake: The only way to create a network of transit-oriented projects and stay away from car-generated sprawl, they argue, is to stop building parking lots. Starve the beast, in other words. Urbanist blogger Ben Schiendelman wrote recently that “for every parking space we build at a transit station, we’re encouraging a new car-oriented suburban housing unit, demand for suburban shopping and suburban road extension to serve them.”

Most of the area’s business and development community is adamantly opposed to starving the parking beast. The Seattle Times, the dominant local newspaper, argues that the 25-year blueprint should “plan for continued use of the automobile despite the anti-car zealotry in vogue at Seattle City Hall.”

The dispute won’t be resolved for a long time. But it suggests a Catch-22 of transit planning that is emerging in many places in the age of Shoup: If you start by building huge parking lots next to transit stations, you may never be able to switch to transit-friendly development. But if you don’t build the lots, what will happen in the short run is that people won’t be able to get to the stations to use the system.

This has been a perplexing issue in the Washington, D.C., suburbs of Northern Virginia, where a new transit line with five new stations opened in 2014. The Silver Line’s planners wanted a future in which transit riders would live near the stations in pedestrian-friendly developments and walk to catch the train. So they didn’t provide parking at four of the five stops. This is totally consistent with the Shoup doctrine. But for the most part the cutting-edge mixed-use developments haven’t happened yet. In the meantime, without a park-and-ride option, potential riders have stayed away. Projected to attract 25,000 weekday boardings, the Silver Line barely reached 15,000 in its first year.

Cities that already have transit stations in walkable neighborhoods have a different set of issues to consider. Their problem is the antiquated planning rules that require a minimum number of parking places in any new residential development. Most cities have traditionally required two spaces for every apartment or condo unit; some set the minimum a little lower, some higher. But at a time when cities are eager to create new housing designed around transit, what those rules mainly do is make residential projects more expensive to build and more expensive for the people who want to live in them.

There is something simple and effective that cities can do about this. They can repeal or at least soften the parking requirements. Chicago has been doing that. Up until recently, it had a one-space-per-unit rule -- relatively sane compared to what some cities had, but still out of touch with evolving urban realities. Prodded by an activist alderman, Proco Joe Moreno, the city council has twice changed the rules in recent years to ease the parking mandate for buildings as far as 1,320 feet from a station -- a quarter-mile -- and eliminate it altogether in some circumstances.

By some estimates, Chicago has increased tenfold the area of the city where the old parking requirements don’t apply, and it has brought its parking rules closer to those in place in Boston, New York and Philadelphia. The strategy appears to be achieving the desired result: The city says that since 2013 more than 20 residential projects have taken advantage of the looser requirements.

All of this progress still stops short of Shoup’s most fundamental and radical proposal: that cities systematically limit the number of parking spaces in the central city and charge higher prices for the ones that remain, all as a way of inducing people to do less driving. One city has become relatively famous for doing this. Portland, Ore., stopped adding downtown parking in the 1970s. A quarter-century later, with a significantly larger population, it had roughly the same number of spaces it had started with. This didn’t prevent downtown Portland from experiencing dramatic commercial and residential success in the years after the policy was implemented. But not many other cities have been willing to mount such a direct challenge to driver sensibilities.

Still, quite a few have begun to at least nibble around the edges of Shoupism. Several years ago, San Francisco initiated what it calls SFpark, a technology-driven system that divides each working day into three distinct periods and charges different prices for a parking space depending on when during the day a driver wants to use it. The prices are adjusted regularly to take account of driver demand. The goal is to reduce overall parking usage to roughly 70 percent of capacity, so that a space is almost always available for somebody who really needs one. San Francisco is calling SFpark a success. Washington, D.C., has been experimenting with a similar idea in selected busy neighborhoods in the city.

There are other schemes floating around that trace back to the Shoup doctrine. One is to let developers pay a fee to city government in lieu of providing parking. Another is for employers to offer their workers cash payouts rather than giving them a parking subsidy. Earlier this year, a developer in San Francisco promised tenants $100 passes for the city’s transit system or for Uber rides in exchange for doing without a reserved space.

All in all, the past few years have been a fruitful time for a set of ideas that once seemed odd and to be outside the realm of practicality. Shoup himself is semi-retired, but he is as single-minded as ever. “Minimizing parking requirements,” he wrote earlier this year, “may be the cheapest and the simplest way to achieve a more just society.”

I’m inclined to dismiss that as far-fetched, but not quite as cavalierly as I would have in 2005.