Wiedefeld decided to form a "partnership" with the TSA, averting some of the conflicts that affected other airports. BWI became a testing ground for some of the agency's new procedures and technologies and was able to provide more feedback than airports that simply waited for decisions to be imposed, he said.

In the first wave of the security response, intrusive baggage screening devices were located at the front of the check-in area. BWI officials quickly looked for ways to remove those devices from such a prominent location, he said.

As an architect, Philipsen has noticed that most airports weren't designed for the security functions they must now accommodate. As a result, passengers are often jammed into spaces too small for that purpose. BWI's new Southwest Airlines terminal, he said, is a welcome exception.

David Stempler, president of the Chevy Chase-based Air Travelers Association, said the increased security has prompted some travelers to switch from planes to trains or buses. "Some people are just avoiding air travel because of the hassle factor."

Marc Rotenberg, executive director of the Electronic Privacy Information Center, is one of those travelers. He takes trains whenever he can because going through airports has become a less-pleasant experience.

But even on Amtrak, he said, the government has stepped up surveillance. "You see with trains, especially in New York City's Penn Station, there's much more random inspection of travelers."

Wiedefeld, who later moved to the Maryland Transit Administration, said that agency decided to concentrate on security measures that wouldn't be visible to the customers. For instance, he said, the TSA provided a grant for state-of-the-art devices that set off an alarm if anything brought onto the platform appears big enough to prompt concerns.

The transit-riding public also has become much more aware of security issues such as unattended packages, Swaim-Staley said. "These kind of things get reported now, and they're taken very seriously."

While most Marylanders never have to deal with security at the port of Baltimore, those who work there have seen dramatic changes since 9/11. For example, the security cameras mounted on the fence of the Dundalk Marine Terminal — once wooden decoys — are real.

Before the attacks, security at the marine terminals was primarily aimed at preventing cargo theft, Swaim-Staley said. That shifted with the concern that ports could be an avenue for terrorist attacks.

Security changes would take years, however. As late as 2005, the fences at some terminals were in shoddy condition, electronic warning systems were unreliable and electronic camera surveillance was spotty. Only in recent years has the Coast Guard given the port stellar ratings for its security.

The Rev. Mary H.T. Davisson, executive director at the Baltimore International Seafarers Center, said the former wave-through security at the port has become progressively tighter for the chaplains and volunteers who call on the crews of cargo ships.

For her ministry, that has meant going through several versions of new state identity cards before finally having to acquire the federal Transportation Worker Identification Credential — the same tamper-resistant biometric cards issued to longshoremen and truckers at the port. It has also meant going through extensive training on the rules for escorting crew members off the terminals for shopping and other breaks from shipboard life.

"It's not unusual for us to wait a half-hour" as security officials check the identification of each seafarer in one of the center's vans, she said. "That has really been a game-changer."

Some forms of transportation remain relatively unaffected by post-9/11 security measures. The experience of riding in a car has changed little, except for the occasional electronic message signs calling for drivers to report anything suspicious.

But even here, there are subtle changes. Swaim-Staley said both the Maryland Transportation Authority and State Highway Administration are keeping a closer watch on bridges and tunnels. And new layers of security and screening, including background checks of potential employees, have been added at the Motor Vehicle Administration.

Porcari said the federal government is working to make the process less onerous for travelers. As recently as last month, the TSA, responding to complaints, installed new screening software at BWI and other airports designed to make passenger images less explicit in showing bodily contours.

"I want the front end — the customer end — to be as close as possible to the same status, where it's safe, it's efficient, it's customer-friendly," Porcari said.

But Rotenberg questions whether more rigorous screening has had any payoff. "One big question is fairly obvious: Is this making us any safer?" he asked. In his judgment, the answer is no.

Stempler believes air safety has improved, not only because of airport screening but also as a result of greater awareness by passengers and crew, and more secure cockpits.

"Is it a perfect system? No, not yet. The multiple layers of security we have really serve passengers well," he said. As screening technology continues to improve, such irritants as the shoe-removal requirement might soon become unnecessary, he added.

Philipsen said the stricter security measures haven't made a huge difference in the quality of travel, and he appreciates the courtesy of most TSA workers, especially compared to what he's seen in other countries.

"Generally I understand why it's done, and one can adapt to this," he said.

But that matter of taking off the shoes — a legacy of the infamous "shoe bomber" Richard Reid's botched attempt to blow up a trans-Atlantic airliner in December 2001 — still rankles.

"We are always going after the last threat and missing the next one," Philipsen said.