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"maximum theoretical running speed" for human beings. (Evolutionary biologist E.O. Wilson has drawn similar conclusions.) "This is of interest," he says, "because it suggests that our physiology and psychology has evolved based around the potential maximum impact on the speed of human beings." The ramifications go beyond safety, says Hamilton-Baillie, to bear directly on the interplay between speed, traffic controls and vehicle capacity. Evidence from countries and cities that have introduced a design speed of 30 kilometers per hour (about 18.5 mph) -- as many of the European Union nations are doing -- shows that slower speeds improve traffic flow and reduce congestion. "This surprises many people, although mathematically it's not surprising," Hamilton-Baillie says. "The reason for this is that your speed of journey, the ability of traffic to move smoothly through the built environment, depends on performance of your intersections, not on your speed of flow between intersections." And intersections, he says, work much more efficiently at lower speeds. "At 30 miles per hour, you frequently need control systems like traffic signals, which themselves mean that the intersection is not in use for significant periods of time. Whereas at slower speeds vehicles can move much more closely together and drivers can use eye contact to engage and make decisions. So you get much higher capacity." Combining slower speeds with a reduction in traffic controls, in other words, may have more than public safety and shared-space benefits. It also appears to profit the driver. (This is the logic behind the modern roundabout, a redesigned version of the classic traffic circle that is replacing signalized intersections in the United Kingdom and is gaining acceptance among transportation officials in the United States). "You can see this is the way to break out of the pro-car, anti-car debate," Hamilton-Baillie says. "Because the shared approach very much accepts the car as a vital useful component in cities that will remain with us for some generations to come." Let's return to China for a minute. If traffic in the world's most populous country provides a useful comparison and contrast, it's because second-generation traffic calming isn't about anarchy; it's about studied anarchy. In essence, Hamilton-Baillie is advocating for a new field: one that blends traffic engineering with urban design. Or, as he titled an upcoming paper: "Urban Design: Why Don't We Do It in the Road?" There's a place for highways and roads dedicated solely to the movement of automobiles, he says. Just not in the city, where streets constitute 70 percent of all public space. "You have to have a completely different approach to the design of streets in the broad urban realm," he says. "You have to make an absolutely clear transition between those roads that are necessary, the state-controlled and legislative world of the traffic environment, to the human-controlled, culturally controlled world of the city, where you pick up your rules not from what you're allowed to do, but from a