Zsofia Csaba, a waitress at the Sanctuary pub, rode the subway to work every day until July 7, the day bombs exploded on three Underground trains and a bus, changing the rhythm of her life and her city. Since then, she has ridden a bike, preferring not to use a transit system where 52 passengers and four presumed bombers perished and 700 people were injured.

"What is going on right now is quite scary," said Csaba, 20, who has joined a new fleet of commuters riding to work on two wheels.

One month after the terrorist attacks, London is trying to get back to normal but finding life has changed. Guests in some hotels are searched and wanded with metal detectors. Thousands of police officers patrol the streets. Every siren from every passing ambulance or firetruck makes Londoners wonder if it has happened again. And record numbers of people are taking to bikes and skateboards or simply staying home rather than using one of the world's most storied public transportation systems.

Tim O'Toole, a former Philadelphia rail executive who runs the Tube, as the London subway is informally known, said in an interview that ridership was down 15 percent during the week and 30 percent on weekends. O'Toole said the greater drop-off has come from weekend and holiday travelers who ride the trains by choice rather than necessity.

O'Toole said that ridership after the July 7 bombings "snapped back" but that the attempted attacks on July 21, in which bombs failed to detonate, had a larger impact. However, with a heavy police presence and 6,000 security cameras in the subway -- and plans to double that number -- O'Toole said he was confident that the angst in the subway would subside.

Nearly 3 million people a day continue to rely on the Tube as the only affordable option to get around London, where gasoline prices hit nearly $6 a gallon this summer and the parking and tolls make Manhattan seem like a deal. Just to drive a car into the downtown area rings up a daily toll of nearly $15. An extraordinary 85 percent of commuters into central London take public transportation, far more than in any other comparable European city, according to transit officials here. In Washington, about 700,000 people ride Metrorail every day.

"For people like me who have to use the Tube every single day, being terrified is not an option," said Jack Shenker, 20, an Oxford University student who said he could not get around London any other way. "Everything appears to be normal, but there is a different mentality -- people are wary," he said while seated on a crowded train Monday morning. "Tube journeys are not as enjoyable as they used to be."

Many others interviewed aboard trains agreed with Shenker that the subway was not the same. People used to lose themselves in crossword puzzles and newspapers. Now, passengers lock their eyes on anyone who seems suspicious until the person gets off. Many South Asians, who come from the same area as the presumed bombers, as well as other young men carrying backpacks, have told television interviewers that they no longer feel comfortable riding the subway.

"Everyone is observing everyone else and checking out everyone's bags," said Christina Roeder, 25, an office worker. After the July 7 bombings, she stayed home one day, rode the bus the second, but then returned to her routine, "only nervous and different now."

The huge police presence in the stations, the constant security announcements over the public address system and the almost daily shutdown of some stations because of a report of a suspicious package have all changed the atmosphere of the world's oldest underground railway system, which dates to 1863.

A guitar-strumming middle-aged man with hair falling down his back was happily playing a tune aboard a train on the Circle Line on Monday, talking about how music men like him were needed now more than ever. But as he finished his last chord, the man standing beside him, wearing a T-shirt and tennis shoes and carrying a backpack, flipped out his police badge and ushered him off the train. Buskers, it turns out, may play only in a designated area, and this was no time to break the rules.

That only adds to the reasons that Owen and Sheila Atkinson, both 76, spend their day above ground. They took a six-hour stroll along the Thames River, preferring that to the subway and saying they saw "fewer people" strolling around the tourist sites than at any comparable time in years.

Terry Jones of Action Bikes in central London said business was booming. Some stores are reporting a tripling of sales, and Jones said people are not only buying new and used bikes but "getting cycles out of the shed that they haven't seen in years."

Sarah Gibson, 24, who works in sales for a catering company, is another convert to bicycling. "I tried Rollerblading for one day, but I realized I didn't know how to stop," she said. So she bought a secondhand bike. When she's forced to bike through the rain on her hour-long commute, she said, she figures she will just jump in the shower once she gets to work. "At least I will be in one piece and a lot less stressed," she said.

But Jamie Hawley, who runs the Mister Softee ice cream truck on Queen's Walk at the foot of the landmark Tower Bridge, may have the most inventive alternative to the Tube. He commutes in his blue-and-white van, decorated with two large ice cream cones above the windshield. "No bombers are going to hit Mister Softee," he said. "Unless, of course, they want an ice cream."

A lone commuter waits for a train at the Russell Square station. Weekday ridership on the Tube is down 15 percent. Dan Gabay prepares to test-ride a bicycle at a shop in central London. Business is booming at bike stores since the July attacks, with some reporting a tripling of sales.