The trouble unfolded in different ways for passengers riding the No. 15 bus up Belair Road on April 19.
Seated near the rear with her sleeping 22-month-old son, Dajun, on her lap, Erica Smith first spotted the thick smoke funneling up outside the windows. To Norma Powell, the trouble began when the bus abruptly lurched. And Chanel Harrison heard it as a muffled explosion.
Flat tire? Mechanical breakdown? Those were their first guesses.
But, for Catherine Cody, waiting in her Dodge Durango sport utility vehicle at the nearby intersection, there was no mistaking what was going on.
"We heard a little grunty noise, and then we saw the tire," she said. "It was hurtling through the air, and I just knew it was going to break out a window."
Cody is a praying woman. "I put up my hand and said, `Oh Jesus,'" she remembers.
Maryland Transit Administration Bus 9417 became the ninth to lose a set of rear wheels since August. The next day, wheels came off a 10th bus, and acting MTA Administrator Virginia White began an investigation. She said she was unaware of the pattern of failures until that day.
Since then, seven more buses have lost wheels, the most recent on Friday.
State Transportation Secretary John D. Porcari has sent an independent investigative team into the MTA garages and administrative offices to identify the cause, as well as the reason why an aggressive investigation didn't begin sooner into a problem that is extremely rare and dangerous. On Saturday, White began an indefinite leave of absence as Porcari's team moved forward.
Not all of the buses fell apart as spectacularly as Bus 9417, which propelled two 200-pound wheels and a hefty brake assembly through the intersection of Belair Road and Elmora Avenue.
On Feb. 21, when the right rear wheels fell off a bus at York Road and Belvedere Avenue about noon, bystanders considered it more amusing than dangerous. Instead of rolling away, the wheels fell over by the curb, attracting chuckles from the lunchtime crowd.
"We heard the sound -- it was a loud noise like a screeching," said Allfirst Bank branch manager Carolyn Valentine, whose desk overlooks the intersection. No one was hurt in the accident. "It was so funny, the wheels just flopped over, " Valentine said.
But Cody wasn't nearly as amused when Bus 9417 passed in front of her. It was 4 p.m., and she was carpooling with three co-workers to their night cleaning jobs at Fort Meade. Waiting at the stop sign at Elmora Avenue, she prepared to turn south onto Belair Road.
"When I looked to the left, I could not believe this tire was coming," said Cody. The first wheel hit the driver's door of her SUV.
"It rocked the truck and then bounced back up the street," she said. "Then here came the brake drum rolling up. Then here come another tire and it hit me across the front of my truck, and that rocked us also."
The bad news: $1,742.60 in damage to her two-year-old, champagne-colored SUV.
The good news: Neither wheel struck the car windows. Cody says she believes her prayer worked.
"I said, `Thank you, dear Lord, for that,'" she said. "I knew if it hit that glass, I wouldn't have been here today."
In the Toyota Corolla to Cody's right, 27-year-old Richard Matthews had his car's speakers cranked up as he prepared to turn right onto Belair Road. He didn't hear the screech or see objects flying. But he felt the impact.
For an instant, he thought he must have nosed his car too far into traffic and been struck by the passing bus. Then it occurred to him -- his car hadn't moved.
He climbed out, noticed the bus brake drum in the middle of the street and then discovered a wide white gash across the center of the driver's door, where the drum had crashed and scraped away the maroon paint.
"I just couldn't believe it," Matthews said. "My immediate thought was, I'm glad it was on Belair Road and not on a highway. Those wheels are about 4-feet high. That's definitely a major concern, not only for people outside the bus, but those on the bus, too."
Whatever the impressions of the approximately 20 passengers inside Bus 9417, they kept it to themselves during the first seconds.
"They didn't say nothing, they just got up and ran," said Smith, 18, of the Gardenville neighborhood of Northeast Baltimore. Juggling her toddler and two book bags, Smith raced forward toward the exit, nearly dropping little Dajun.
In the rush to escape, passengers said, it never occurred to them that the bus might have lost its wheels. Terrorism seemed more plausible.
"I didn't know what it was, but we thought it was a bomb or something," said Sharon Yancy, 45, of East Baltimore, who had been on her way to pick up a prescription. "I was scared. We were just shaking."
Norma Powell's fears were more specific.
"I thought maybe bin Laden's up to it again," she said.
Most of the passengers were high school students returning home from classes. Matthews said the bus driver immediately got everyone off the bus and sat them down.