"The terrorists are going to target the highest priority soft target. Well, it used to be that airlines were the soft target. They're not anymore," says transportation scholar Rod Diridon, who recalls that 10 years ago there was no TSA and flying was much less of a hassle.
But when the unthinkable happened on that Tuesday morning, it changed air travel forever.
"That's where TSA came from is out of 9/11," says Diridon.
The TSA was founded with two missions -- to keep the skies safe and to reassure the traveling public. Over the past 10 years both have occasionally been a challenge.
Passengers were forced to remove their shoes after the al Qaida shoe bomber made it through security. Then, the TSA banned liquids from carry-ons after word of a new threat. And, the so-called underwear bomber prompted the rollout of what the American Civil Liberties Union called naked body scanners.
"I think the outrage was quite widespread, and you got that from across the political spectrum," says Linda Lye with the ACLU.
A software update addressed some privacy issues, but didn't eliminate concerns over intrusive patdowns.
"Right now, the terrorists are winning when it comes to this security situation, to make us accept intrusiveness, but it's a necessary intrusiveness," says travelers' rights attorney Al Anolik, who says that in this case, he believes the right to privacy comes second. "There are those out there that want to kill us, and I would rather fly protected."
Indeed, nothing is truly private when you fly anymore. Unlike 10 years ago, automated x-ray machines now scan every checked bag and instantly pull it off the line if something looks fishy.
A side of airport security you don't usually see is located in a heavily secured room deep inside the San Francisco International Airport, where any bag that looks suspicious on an x-ray is sent down a conveyor belt to be opened up and inspected by hand. Once a bag arrives, federal employees look inside and search for explosives.
And bags aren't the only place the TSA looks for bombs. Soon, you will see more dogs around the airport making sure the terminals are safe as well.
"Not everybody likes dogs, but everybody respects the dog and its mission," says SFO Deputy Federal Security Director James Adams.
Officers have a new mission too -- spotting suspicious people using behavior analysis, both in person and from a new high-tech surveillance room.
"We've found hundreds of various prohibited items and other things that shouldn't be on an aircraft through the various techniques that we're using in behavioral observation," says Adams.
Experts tell us all these tools really have made air travel safer. But now intelligence suggests that terrorists have a new target.
"When Bin Laden was killed in his lair, the papers that were captured targeted U.S. rail systems," said Diridon.
It's a threat BART police have taken seriously. Like the airports, BART has built a new state-of-the-art surveillance center, added bomb sniffing dogs, and now trains its officers to spot a terrorist.
"It's not an attack on BART, it's not an attack on the Bay Area, it's an attack on America," says BART Police Lt. Kevin Franklin. "And we are part of the defense in protecting America and America's critical infrastructure."
Sitting in the train station that's named after him, Diridon pointed out there's even more being done that you can't see.
"As you go through many of the turnstiles now, there are everything from scanners, x-ray scanners to visual scanners to sniffers," says Diridon.
It's all technology that wasn't necessary back when this station was built. Diridon says he misses those days.
"I hope that we go back to a very open welcoming society that we have been in the past," he says.