The National Museum of the American Indian on the Mall in Washington is a successful example. Cantilevered, curving bands of rough-cut limestone project 50 feet from the body of the building, protecting the east entrance from a crash attack. The sidewalk, which is elevated above the street, acts as another unobtrusive barrier, while nonlinear paths, pools, watercourses, and planted mini-grasslands and wetlands are a veiled – and beautiful – form of defense.
"Nothing is more important to security than people," says Hopper. The more that public amenities lure people to the street, the more this activity creates inherent security, something urban theorist Jane Jacobs called "eyes on the street."
One of the architecture firms most savvy at designing urban streetscapes that are both comfortable and secure is Rogers Marvel Architects of New York City. Their designs for the New York Financial District have raised security to an art form.
The Stock Exchange and Wall Street (potential terrorist targets) are areas of dense foot traffic in lower Manhattan. After 9/11 (and temporarily again during the "Occupy Wall Street" protests), security barriers sealed off the street. The firm's task in 2004 was to restore public space while minimizing the risk of a potential incident. Their elegant, bronze-clad sculptural bollards (called "NoGos") are not only appealing but also muscular, able to stop a 15,000-pound truck traveling 50 miles per hour. For approved vehicular access, the firm designed perforated bollards that glow red or green to signal "stop" or "go" atop a turntable inlaid in the pavement. "Like your aunt's Lazy Susan," Robert Rogers says, the turntable and bollards rotate to grant passage when desired or impede it when necessary.
Another clever intervention is a "Tiger Trap" made of collapsible concrete installed near the World Financial Center. Adapted from arrestor beds used at the end of short runways in airports, the concrete is engineered to fail under the weight of a truck bomb but is invisible to pedestrians walking atop it on planting beds or plazas.
"The most interesting things are not what's been done before," Mr. Rogers says. "What they teach in architecture school is problem solving. That's the adventure of being an architect – where the intrigue and excitement lie."
The plan for a new US Embassy in London illustrates how a standoff zone does not mean standoffish design. The KieranTimberlake architectural firm of Philadelphia recently won the commission with their design for what James Timberlake calls "an urban building in an urban park." The building itself will be a see-through cube atop a colonnade, surrounded by curving paths, trees, berms, gardens, and a pond that acts as a moat. Instead of being foreboding, the blast-resistant glass and polymer skin of the building creates, Mr. Timberlake says, a welcoming, crystalline "beacon," an "open, transparent, sustainable icon of democracy." Timberlake calls the security requirement not a "constraint but an opportunity." By incorporating it in the design process rather than as an add-on or afterthought, he hopes their approach "will have a transformative effect on the expression and presence of barrier design."