A decade ago, Beijing seemed like a cyclist’s paradise. True, there were no dedicated bike lanes, but that was because two-wheeled, man-powered vehicles owned the road. In what seemed like a scene from an environmentalist’s (slightly socialist) fantasy, scores of bikers would wait patiently for the light to change, then embark en masse for their destinations. By contrast, biking around my hometown of Boston seemed faintly crazy -- an invitation to being sideswiped by one of our famously considerate drivers.

Today all that has been turned on its head. When I went to rent a bike upon my arrival in Beijing last week, people looked at me as though I were mad. As I tooled around the old neighborhoods near the Forbidden City, I was often the only nonmotorized thing in sight. There were bike lanes, all right, but they were populated only by motorbikers and the occasional fellow intrepid Westerner. On the back streets, I saw a few older Chinese cyclists, wearing expressions of thorough disgust. Meanwhile, Boston, like lots of other U.S. cities, has become a reasonable place to bicycle. I still wouldn’t recommend it to the faint of heart, but as long as you bike defensively, you feel like a member of a forward-looking tribe of change agents.

Transportation Revolution

The story of China’s transportation revolution is an allegory of unexpected consequences and perverse incentives. It’s also an invitation to think about what happens when markets take hold in an environment unaccustomed to them.

Start with the good news: As China has gotten rich, its people (at least in the cities) have gained access to goods that their grandparents never dreamed of. Cars are an amazing invention, which is probably why they haven’t changed much in the century since they began to be mass-produced. You can go farther, faster, drier and warmer in them than in any form of transport since the dawn of humanity. What’s more, you can go wherever you want -- a terrific aid to free choice and individualism.

Yet one effect of proliferating cars is that they worsen street pollution. Exhaust is far from the only contributor to Beijing’s now-legendary smog -- coal-burning steel plants and other factories on the urban periphery do their part -- but on the street, it’s the output of tailpipes burping their low-quality gasoline that hits you in the face. After three hours on the road, my throat was burning with acrid smog. I felt like I had smoked a pack of cigarettes. And all this was on a day when the rate of particles smaller than 2.5 milligrams was only about 135 per million -- much lower than the 600 ppm that Beijing has reached in extreme conditions.

The bad air quality drives people into cars, which makes the air quality worse. And once you have a car, you can drive to work from greater distances. Commuter traffic not only kills the air but also clogs the roads. Traffic has gotten so bad that the municipality has instituted a “drive every other day only” rule.

People who can’t bike without choking, and are banned from driving, throng to the subways. Riding two of the main lines, 1 and 10, at rush hour, I found them clean and efficient. And, oh yes, more crowded than any train I have ever been on in any city on Earth. Etiquette hasn’t yet solved the “how many people can fit in this car?” problem. At one point, I saw several eager customers take a running start and fling themselves into the train like special-teams blockers heading down the football field. Or actually, I felt it. The impact rebounded through the train to the point where I momentarily wondered if someone might be crushed. Getting out wasn’t any better because no one wants to make way, knowing how hard it will be to remount. The Beijing subway will have to be drastically expanded, but I can easily imagine preferring to sit in traffic with glass and steel between me and my fellow humans.

Individual Choice

That, of course, is the point: Driving is the optimal individual choice, given the conditions created by everyone else’s individual choices. The market prefers cars. More market, more cars. And the effect of the free market in transport choices is a disaster in the making. Everyone I saw in Beijing had a smartphone (they work in the subway!). And every English speaker I met had an application that provided two numbers: the U.S. Embassy’s estimate of the air quality, and the Chinese government’s counter-estimate. Information is wonderful: the higher the number, the better advised you are to take a car and stay out of the air.

Regulating the transportation market distorts individual choices. Bike lanes in Boston’s narrow streets slow down cars that are already crawling. They enrage the Boston driver because they constrain his God-given freedom to cut the line of traffic from the side like a modern Paul Revere evading British patrols on his way to Lexington. They benefit the few on bikes, not the many who drive the market.

But market regulation is necessary where collective action leads to rational madness. China has made amazing progress by bringing the market and its individual choice into daily life. It needs more experiments in that direction, and more individual freedom to go with it. But it also needs to notice where the free market must be managed. Bring back Beijing’s air, and bring back its bikes. A one-party state must be good for something.

(Noah Feldman, a law professor at Harvard University and the author of the forthcoming “Cool War: The Future of Global Competition,” is a Bloomberg View columnist. Follow him on Twitter. The opinions expressed are his own.)

To contact the writer of this article: Noah Feldman at noah_feldman@harvard.edu

To contact the editor responsible for this article: Francis Wilkinson at fwilkinson1@bloomberg.net