Carpooling mandates. Nightmarish commutes. Police checkpoints. Office building bag searches. Bomb scares.

Welcome to life during wartime.

Since the Sept. 11 terrorist attacks on the U.S., Americans are facing a whole new world, one of tightened security and perpetual tension. Gone in some places is the era of unfettered access and the freedom to roam at will. Not surprisingly, it's New Yorkers who have seen the most change.

Because heightened security in the weeks since the disaster has created traffic gridlock on the island of Manhattan, police Thursday began turning cars with less than two people in them away from the tunnels and bridges leading into the city.

If the two-day test successfully eases congestion, New York Mayor Rudolph Giuliani said the ban might be extended. People have to "get used to living in a different way," he said.

Matthew Wilson, who had dropped off a friend in the borough of Queens and was headed back to Harlem through southern Manhattan, got caught in the dragnet Thursday.

"The cops told me I have to pick up someone to go back home with me," he said.

New York transportation spokesman Paul Kurtz estimated that only 3 or 4 percent of cars were denied access into Manhattan. But most of the rest coped with horrific traffic jams. "It took me 55 minutes to go three blocks," said William Rivera, who drove alone into Manhattan a few minutes before the 6 a.m. to noon ban took effect.

Finding other ways to commute — and battling longer rides to the office — have been only some of the changes people have had to adjust to in recent weeks.

Many Americans have been greeted at city office towers by extra security guards asking them to open their handbags and briefcases. And those who work in skyscrapers have gotten used to regular evacuations and bomb scares.

Truck drivers have been subject to random searches, particularly in New York, where police are being extra vigilant.

Cars and taxis are no longer allowed to stop in front of a number of big city train stations, like 30th Street Station in Philadelphia and Penn Station in New York — making dropping off and picking up passengers trickier. And Amtrak is now requiring riders to show a photo ID when buying tickets, checking baggage or sending packages via train.

Air passengers are also facing longer check-in lines and beefed-up security. Most airlines now require travelers to check in at least two hours in advance for domestic flights.

Life is different in other ways, too. Shopping lists include things that would have been unimaginable a month ago, gas masks for example, and clinics are being inundated with calls about vaccines for anthrax or other potential biological weapons.

Carelessly wandering some streets is even out of the question now. Barricades are still scattered throughout New York's Wall Street area, and San Francisco's Golden Gate Bridge has been closed indefinitely to foot traffic because of safety concerns.

Most Americans welcome and are learning to live with all the security changes, but some are concerned we might be going overboard — and giving into the fear the terrorists hoped to instill.

"Any time Americans alter their behavior because of a clear and visible threat to their lives, those that did the threatening have achieved some portion of their goal," Defense Secretary Donald Rumsfeld said last week.

Fox News' Steve Brown in Chicago and The Associated Press contributed to this report.