In 1995 the Secret Service closed Pennsylvania Avenue in front of the White House. It was a big mistake, because the fortress-like White House already provides good protection against car bombs.

In 1996 the National Park Service wanted to make the closing permanent and put in grass, but fortunately that proposal died.

In 2000 the Park Service was back with a plan to put VIP parking under the closed portion of Pennsylvania Avenue between 15th and 17th streets NW. Again, this proposal didn't go forward.

Now it's 2003, and the feds are asking for $6.1 million in the current budget to test and develop a $15 million construction plan to make the avenue closing more permanent. This time the plan is to break up the pavement and put in gravel [Style, March 1].

This latest idea goes back to misguided thinking behind the original decision to close the avenue -- a decision precipitated by the bombing of the Alfred P. Murrah Building in Oklahoma City in 1995. But the situations are not analogous.

The Oklahoma City bomb was in a truck parked 10 feet from the federal building. The White House is 350 feet from Pennsylvania Avenue. Blast pressure decreases roughly with the square of the distance. This means that pressure on the White House would be far less than one-thousandth of the pressure to which the Murrah Building was exposed. The buildings also are not comparable. The White House was rebuilt for security in the '50s with heavy steel girders, 660 tons of steel reinforced concrete and walls roughly a foot thick. By contrast, most of the walls in the Oklahoma City building were quarter-inch glass.

Because stress decreases with wall thickness, stresses at the White House would be a factor of several thousand less than at Oklahoma City if they were subjected to the same pressure. When the effects of distance and wall thickness are combined, the White House is safer from bomb blasts than the Oklahoma City building by a factor of several million. What's more, trucks aren't even allowed within a three-block radius of the White House. Assuming that the White House windows are laminated tempered glass, the president's house probably wouldn't even suffer a broken window from a car bomb.

Pennsylvania Avenue should be reopened now. Citizens who want to speak against the plan to keep it closed should make their views known at the 12:30 p.m. Wednesday meeting of the National Capital Planning Commission at 401 9th St. NW, Suite 500.

-- Robert L. Hershey

is president of the D.C. Society of Professional Engineers.