"The more you post the evidence of legislative control, such as traffic signs, the less the driver is trying to use his or her own senses," says Hamilton-Baillie, noting he has a habit of walking randomly across roads -- much to his wife's consternation. "So the less you can advertise the presence of the state in terms of authority, the more effective this approach can be."
Contrast this approach with that of the United Kingdom and the United States, where education campaigns from the 1960s onward were based on maintaining a clear separation between the highway and the rest of the public realm. Children were trained to modify their behavior and, under pain of death, to stay out of the street. "But as soon as you emphasize separation of functions, you have a more dangerous environment," says Hamilton-Baillie. "Because then the driver sees that he or she has priority. And the child who forgets for a moment and chases a ball across the street is a child in the wrong place."
The new school of traffic engineering also draws on conclusions from evolutionary biology and psychology:
Subvert, don't attack, the dominant paradigm. Or, as David Engwicht, a shared-spaces proponent in Brisbane, Australia, has written: "Implicit in the whole notion of second-generation traffic calming is the idea that significant social change only happens when we amplify the paradoxical 'submerged voice' as opposed to tearing down the 'dominant voice.' Engwicht, a plenary speaker at the Walk 21 Cities for People Conference in Copenhagen this June, argues that controlling a driver's natural propensity for speed is futile. A more effective approach is to engage the driver by emphasizing "uncertainty and intrigue" in the street environment -- for example, planting a tree in the middle of the street instead of putting up a stop sign.
Safety analysts have known for several decades that the maximum vehicle speed at which pedestrians can escape severe injury upon impact is just under 20 miles per hour. Research also suggests that an individual's ability to interact and retain eye contact with other human beings diminishes rapidly at speeds greater than 20 miles per hour. One theory behind this magic bullet, says Hamilton-Baillie, is that 20 mph is the "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.