TCS Daily


Opening America's Avenue

By Robert L. Hershey - March 6, 2003 12:00 AM

Eight years ago, Pennsylvania Avenue in front of the White House was closed after the Oklahoma City bombing. This happened despite there being no good reason at the time, from an engineering standpoint, for the closure. Indeed, even today there is no good reason to keep America's Avenue closed in front of the White House.

The claimed security justification - a hypothetical car bomb - would not really threaten the White House structure. The White House was completely rebuilt, as a virtual fortress, during the Truman administration with 660 tons of steel and concrete around a nest of heavy I-beams. President Truman said, "Only an earthquake or an atomic bomb could wreck the old building now." With laminated tempered glass in the windows, there is no danger to the White House occupants from a car bomb on Pennsylvania Avenue.

Indeed, the blast at Oklahoma City and any hypothetical blast along Pennsylvania Avenue aren't even really comparable. The first big difference is the distance to the bomb. At Oklahoma City, a large truck full of explosives was parked 10 feet away from the building. Pennsylvania Avenue is 350 feet away from the White House. That's a ratio of 35 to 1. The blast pressure decreases roughly with the square of the distance. Thus the Oklahoma City blast pressure is over 1,000 times greater than the hypothetical explosion near the White House.

The second big difference is wall thickness. At Oklahoma City, most of the wall area was ordinary 1/4-inch window glass. By contrast, the White House has steel-reinforced concrete walls about a foot thick. The stress in a wall under pressure loading decreases with the square of the wall thickness. That means that if the pressures were the same, the stress in the White House wall would be several thousand times less than the stress at Oklahoma City.

Moreover, the weakest part of the building would be the windows. But with laminated tempered glass we wouldn't have to worry about them either. Calculations based on blast testing of laminated tempered glass show that 1/2-inch thick windows wouldn't break from a 500 lb car bomb blast - or even a 3,000 lb truck bomb blast - at the 350 ft distance. Thicker windows would be even stronger. The Pentagon has 2-inch thick laminated tempered glass windows that performed well during the September 11 attack.

You would think that with no danger to the White House occupants, the street would have been reopened right away. Instead it has stayed closed for eight years. By the federal government's own figures, 26,000 cars per day have to be rerouted around the closure. This amounts to an implied cost of tens of millions of dollars per year in people's lost time.

Currently, there is a proposal being considered to make the closure of streets around the White House more permanent. The National Capital Planning Commission has asked for $6.1 million to break up the pavement of Pennsylvania Avenue and put in gravel. The hope is that replacing the avenue with gravel will improve the aesthetic appeal of the area.

There is also a $5 million proposal for a study of building an E Street tunnel on the other side of the White House. The estimated cost of the tunnel is $100 million. But E Street has a setback distance even greater than Pennsylvania Avenue, and E Street has remained open during years when Pennsylvania Avenue has been closed. The proposed E Street tunnel would create an attractive new target for a car bomb attack since it would concentrate the blast for anyone unfortunate enough to be in the tunnel. In daily driving, it would keep citizens from looking at their White House.

And while the closing of Pennsylvania Avenue is the primary example of getting carried away with security, it is not the only one. For instance, many streets around the Capitol are similarly closed unnecessarily.

Engineering judgment needs to be exercised in designing the security systems around potential terrorist targets. But we must remember that security at all costs is always too high a price - in terms of money and, more importantly, in terms of freedom.

The author is President, D.C. Society of Professional Engineers.
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