20 YEARS LATER

Commercial air travel as it had been known for decades ended when four hijacked planes crashed into the World Trade Center towers, the Pentagon and a field in Pennsylvania.

The worst terror attack on American soil led to increased and sometimes tension-filled security measures in airports across the world, aimed at preventing a repeat of that awful day. The cataclysm has also contributed to other changes large and small that have reshaped the airline industry — and, for consumers, made air travel more stressful than ever.

Two months after the attacks, President George W. Bush signed legislation creating the Transportation Security Administration, a force of federal airport screeners that replaced the private companies that airlines were hiring to handle security. The law required that all checked bags be screened, cockpit doors be reinforced and more federal air marshals be put on flights.

There has not been another 9/11. Nothing even close. But after that day, flying changed forever. Here’s how it unfolded. Security measures evolved with new threats, and so travelers were asked to take off belts and remove some items from bags for scanning. Things that clearly could be wielded as weapons, like the box

cutters used by the 9/11 hijackers, were banned. After “shoe bomber” Richard Reid’s attempt to take down a flight from Paris to Miami in late 2001, footwear started coming off at

security checkpoints.

Each new requirement seemed to make checkpoint lines longer, forcing passengers to arrive at the airport earlier if they wanted to make their flights. To many travelers, other rules were more mystifying, such as limits on liquids because the wrong ones could possibly be used to concoct a bomb.

“It’s a much bigger hassle than it was before 9/11 — much bigger — but we have gotten used to it,” Ronald Briggs said as he and his wife, Jeanne, waited at Dallas/fort Worth International Airport for a flight to London last month. The north Texas retirees, who traveled frequently before the pandemic, said they are more worried about COVID-19 than terrorism.

“The point about taking shoes off because of one incident on a plane seems somewhat on the extreme side,” Ronald Briggs said, “but the Precheck works pretty smoothly, and I’ve learned to use a plastic belt so I don’t have to take it off.”

The long lines created by post-attack measures gave rise to the Precheck and Global Entry “trusted-traveler programs” in which people who pay a fee and provide certain information about themselves pass through checkpoints without removing shoes and jackets or taking laptops out of their bag.

DAVID ZALUBOWSKI/ASSOCIATED PRESS This summer, an average of nearly 2 million people per day have flowed through TSA checkpoints. On weekends and holidays they can be teeming with stressed-out travelers. Most travelers accept any inconvenience as the price of security in an uncertain world.