The year 2009 was a terrible year for Detroit, the worst in three decades. Americans bought 10.4 million cars -- 21 percent fewer than in 2008 and a whopping 40 percent fewer than the 17 million or so cars and light trucks sold, on average, in the early 2000s.

This is normally seen as bad news, and anyone who’s visited Detroit lately understands why.

But what if the bad news for U.S. automakers, their workers and the economy of the industrial Midwest turns out to be good for the rest of us?

That’s the argument being made by environmentalist and author Lester Brown.

If fewer cars are being driven fewer miles, America’s dependence on imported oil will decrease, as will air pollution, carbon emissions, traffic congestion, respiratory diseases and the demand for new roads or highways.

Because Americans scrapped 14 million cars last year, there are fewer registered vehicles in the U.S. today than there were a year ago -- about 246 million, according to Brown (pictured below), who is president of the Earth Policy Institute. The U.S. now has more registered cars than licensed drivers, of which there are 209 million.

“When is enough enough?" Brown asks. “Continuing growth in our car fleet is no longer in our national interest or in our interest as individuals.”

What’s more, the drop in car sales may be more than a reflection of a down economy. America’s century-old love affair with the automobile may be coming to an end, Brown said yesterday during a conference call with reporters.

This is a bold claim and, while I’m not persuaded that he’s right, Brown’s ideas are worth thinking about. He says an array of forces -- ranging from urbanization to rising oil prices to the popularity of text messages and Facebook among teenagers -- mean that more Americans are learning to live without a car.

Brown, a lifelong environmentalist, is one of them. He lives and works in Washington, D.C., and hasn’t owned a car in more than 35 years.

Even so, in a city with an excellent (but deteriorating) metro system, he’s in a minority. About 37 percent of households in Washington do not own a car, according to the 2000 Census.

Still, as America becomes more urban, fewer people need cars. More than 55 percent of New York households make do without one, and the percentages are 25 percent to 35 percent in older cities like Boston, Baltimore, Philadelphia, Pittsburgh, Chicago and San Francisco. Cities are discouraging car use by raising parking meter fees, Brown noted. Just this week, Chicago raised rates in the Loop to $4.25 an hour.