Could Sept. 11 Happen Again?

July 30 -- A warning from the State Department of a worldwide increased threat of terrorism that may involve commercial aircraft, plus a warning from the Department of Homeland Security — nearly two years after 9/11, could it happen again?

The federal government has taken steps to improve security at U.S. airports and says it is constantly testing the effectiveness of those measures, but it won't tell anyone the results of the tests.

There is little doubt that security has improved, but some family members of the victims of the Sept. 11, 2001 attacks say people have a right to know how effective the measures have been.

"The airlines and the government are not giving us hard information as to how effective security is," said Stephen Push, whose wife died on the plane that hijackers crashed into the Pentagon. "They'll tell us we're making this improvement or we're making that improvement. It may sound nice, it may even look nice in the airport to see these people in uniform going through the bags, but they have not provided us with the hard information as to how effective it is."

Security experts agree that a lot has been done to plug the security holes that allowed 19 hijackers to get on four commercial airlines on the morning of Sept. 11, 2001, but more could be done, they say.

"Is it harder than before 9/11? Yes," said Brian Jenkins of the Rand Corporation, a Washington think tank on security and international affairs. "In my view, is it hard enough? No, we have a ways to go."

Among the steps that have been taken at airports across the country:

The federal government has taken over security checkpoints, screeners are better trained, and in the last 18 months those screeners have confiscated 6 million banned items.

Checked luggage is now examined for explosives by machine, by hand or by trained bomb-sniffing dogs.

Every large passenger plane in the United States now has a cockpit door designed to withstand bullets and small explosives.