The business of travel is notoriously cyclical. So when recession and terrorism in 2001 knocked it flat on its back, it was just a matter of time before it would come back.

Travel in the United States has been resurgent for more than three years. But there's a difference in this particular rebound.

From booking the trip to the cab ride home, technology has changed the travel experience. Today, technology has become the traveler's constant companion. At its best, it eliminates the bottlenecks of the past, reduces stress and saves time. It's a different story when the robot on the other end of the phone insists you're saying Bulgaria, not Baltimore.

Machines today may provide as much or more customer service to airline passengers, hotel guests and rental car customers than humans do. It's now possible to check into a hotel room — or order a drink at the bar — without coming in contact with a hotel employee. It's possible to rent a car without human interaction. And many air passengers reach the jet bridge at the gate before encountering an airline employee — who scans their boarding pass with a machine.

Machines have been taking over from humans in other service industries for years. You can buy a gallon of milk at the market or a gallon of paint at Home Depot without a cashier by using a self-serve device at checkout. Many people are so hooked on ATMs, they never set eyes on a bank teller.

But customer service technology has taken hold in the travel industry only in the last few years, partly because of strong labor unions and tradition. In the disastrous travel downturn following the Sept. 11 attacks, airlines fighting for financial survival cut 150,000 jobs and replaced many with technology.

Voice-recognition software and travel Web sites took the place of many airline reservation agents. Some ticket agents were replaced by self-service check-in kiosks at airport. Although the changes cost thousands of jobs, airlines found that many travelers love the impersonal devices that let them zip through the airport.

A look at how technology is changing the travel experience:

HOTELS: SELF SERVICE

Hyatt Place, a new limited-service hotel chain launched two years ago, shows where hotel technology is heading.

There, guests check in and get their room key from a kiosk in the lobby. They order a snack from the kitchen and pay for it using a touch screen. They have the option to order up a sitcom they just missed on network TV. Before leaving for the airport, guests may stop by the lobby kiosk to print out their boarding pass.

New technology is sweeping through hotels up and down the luxury scale. It's caught on especially with younger travelers, who have grown up with automation. Hilton surveys show more than a third of its customers carry an iPod, 89 percent carry a cell phone, and 49 percent have a high-definition TV at home.

"Our guests are coming in with new expectations, because the technology has really arrived," says Hilton Hotels executive Robert Machen.

The hotel industry postponed investing in major remodels after the 9/11 attacks, when travel plummeted. In 2004, when hotels started making money again, technology and customer acceptance had evolved to the point where tech upgrades made sense.

Those self-serve kiosks are popping up in hotel lobbies everywhere. Hyatt has them at 70 hotels. Hilton has them at 412 Hiltons and Embassy Suites. Marriott will have them at 40 hotels by January, and will test them at Courtyard hotels this year.

Tabletop computers may become common. Sheraton is installing them in lobbies and bars of its biggest hotels. Produced by Microsoft, the touch-controlled, waterproof computers go for $10,000 each. The horizontal screen and controls are flush with the tabletop, so they double as ordinary furniture. Guests may use them to order a drink or access the Internet to find directions or the closing time for a nearby museum.

Boutique chain Thompson Hotels will install a James Bond-style security feature at two new sites: a room lock system that reads a guest's fingerprints before opening the door.

They're coming to Thompson Lower East Side in Manhattan, which opens in February, and Thompson Toronto, set to open in early 2009.

Thompson co-owner Stephen Brandman says they're installing the locks in just two hotels initially to make sure they work. Employing the "latest, greatest gadget" can backfire, he says, if guests get confused or a device malfunctions. Not surprisingly, hoteliers are investing most heavily in entertainment, equipping rooms with large, plasma-screen, high-definition TVs. Hilton's research shows that nearly 98 percent of guests have the set on for more than three hours a day. Guest rooms at all J.W. Marriott, Marriott and Renaissance hotels will have high-definition, flat-panel TVs by the end of 2009.

Technology has even invaded the bathroom. The Westin Chicago River North is testing the Brondell Swash 800, a $1,000 throne that combines a toilet with a bidet. It has a heated, germ-resistant seat, uses warm filtered water to wash, and a dryer to finish.

AIRLINES: BYE, PAPER

Paper tickets may go away.

The airlines' widespread use of new technology has had at least as much to do with cutting costs as with improving the customer experience. In nearly all cases, the increased use of technology has allowed airlines to reduce the number of employees needed to interact with passengers.

The most noticeable change has come in ticketing. By May, it will be almost impossible to buy a paper ticket from any airline in the world.

That's a big change from 2000, when about 59 percent of all tickets sold in the United States were "paperless." Last month, that figure was 99 percent.

In the future, the paper boarding pass could become as rare as a paper ticket. Air Canada said last week that for many of its non-U.S. flights, it's giving travelers the option of getting what essentially is a picture of a boarding pass bar code on their cell phones. To board, a traveler can call it up on the phone's screen and pass it under an electronic reader. The system is also in limited use in Asia.

Many travelers have come to appreciate the ability to check-in via the Internet before leaving home or the office. Many also like airlines' flight status notifications sent to cell phones or computers hours in advance of departure time.

But not all travelers think new technology is friendly. Ron Stagner, a regional sales manager who travels about 40 weeks a year on business, hates lengthy voice menus and Web sites delayed by slow-loading graphics. Dealing with technological overkill "takes a lot of time I don't always have, especially if I'm changing flights," he says.

Fernando Mariano, an international public relations executive from Orlando, Fla., says trying to navigate the voice-recognition systems that most airlines now use to answer calls can be daunting for those, such as him, who are not native English speakers.

"When offering voice recognition, airlines should also offer an option to use the keypad," he says. (Hint: Speaking the word "agent" or "representative" usually prompts the system to transfer you to a human.)

Competition is pushing the evolution and expansion of in-flight entertainment technology. When it began flying seven years ago, JetBlue was the only U.S. carrier offering live television programs. Several carriers, including Frontier; Virgin America; and, on transcontinental flights, Delta, now offer similar programming. Others are watching consumer reaction to decide on following. Holding them back: costs of retrofitting hundreds of planes with systems that can cost up to a $1 million per plane.

In the meantime, enhanced versions of existing in-flight entertainment technology are moving into airline cabins — especially business class and first class, where airlines can charge higher fares.

Most now offer a wider variety of movies, music and TV shows in premier cabins.

The next frontier: in-flight broadband service. In 2006, Aerospace giant Boeing shut down its money-losing broadband service, which had been available to passengers on several foreign carriers. But now, airlines and service providers are making a new push to make the service available to passengers. They're working with improved technology that costs less to install and maintain.

CARS: LOOK, NO LINES

Rental car companies are looking to technology to improve efficiency and save travelers' time.

At three airports, Alamo Rent A Car last year began testing self-service kiosks that allow travelers to avoid lines at rental counters when checking in. The company now has 152 kiosks at 60 airports. Hertz opened its first eight kiosks at Orlando's airport this month.

Avis said this month that it has a new online booking tool that will make it easier to make, check or change a reservation with a BlackBerry or other Internet-enabled portable device. In the past, data sent from the Avis Web site did not fit mobile devices' small screens.

Inside rental cars, upgrades such as improved navigation systems, toll-collection devices and satellite radios make drives more relaxing. The devices also bring in extra revenue for car rental companies. All charge daily fees for the navigation and toll-collection devices, and Hertz charges for satellite radio.

In January, Avis announced a portable device that, for $10.95 per day, provides wireless Internet access. The device plugs into a car's power outlet or uses another plug for any electrical outlet, providing Internet connectivity "anywhere," including hotels and restaurants.

Renters can also get wireless Internet at 40 Hertz airport locations for $4.95 daily.

Hertz introduced the first navigation systems in 1994. It now has more than 60,000 NeverLost units in service. Traveler Larry Hotaling, who assists companies entering the Asia market, says Hertz's NeverLost system is great to have in an unfamiliar city. He says it "definitely saves you from getting lost and also helps in avoiding dangerous areas."

The seven other major car rental companies also offer navigation systems. National and Alamo began offering them in January, and Enterprise introduced its Garmin StreetPilot c340 system last year.

Avis last year unveiled a "Where2" system, which, it said, was the first navigation system with "real-time traffic alerts and Bluetooth connectivity." A Garmin navigation system introduced by Dollar Rent A Car and Thrifty Car Rental in July offers traffic information and Bluetooth connectivity. Business traveler Jeff Griffin, of Connersville, Ind., likes a navigation system and a satellite radio in his rental cars. "I enjoy having both in the car so I don't have to take mine," says Griffin, who is in the software training business.

Electronic toll payment began appearing in rental cars last year when Avis and Budget installed transponders in vehicles at 117 locations in the New York and Houston areas. The companies expanded the program to all locations in the Northeast, Chicago, Florida, Colorado and Puerto Rico. Renters pay $1.50 to $2 daily, plus tolls.

Hertz offers electronic toll payment for vehicles rented at 10 East Coast airports, its Manhattan locations and in Houston.