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A bus operated by a discount company with a particularly poor record of fatigued driving overturned on a Virginia highway before dawn Tuesday, killing four people and injuring more than 50 others.

The driver was charged with reckless driving, and police said fatigue was a factor. The National Transportation Safety Board is investigating.

The SkyExpress bus swerved off northbound Interstate 95, hit an embankment and flipped just before 5 a.m. about 30 miles north of Richmond. Fifty-four people were taken to area hospitals and treated for minor to severe injuries.

The bus left Greensboro, N.C., on Monday night and was headed to Chinatown in New York City with 59 people aboard. The driver, Kin Yiu Cheung, 37, of Flushing, N.Y., was being held in an area jail on $3,000 bond.

The company offered its condolences to the families of the four women killed and said it would cooperate fully in the investigation.

"This is the first serious accident" involving SkyExpress buses, the company said in a statement released through its media liaison, Gail Parenteau. "The bus driver has never before been involved in an accident."

Many bus operators eschew terminals to offer cheap East Coast fares, providing convenient routes and in some cases free wireless Internet. The industry is in the fifth year of a solid boom, but recent fatal accidents have prompted calls for tougher regulation.

In a March crash, a speeding bus operated by another company toppled off an elevated highway in New York and hit a utility pole, peeling off the roof, as it was returning to Chinatown from a Connecticut casino. Fifteen passengers were killed and 18 injured.

Charlotte, N.C.-based SkyExpress, which offers $30 trips from New York City to several Southern cities, had 46 violations for driver fatigue since 2009, three of them serious, according to Federal Motor Carrier Safety Administration records. The agency said SkyExpress ranked worse than 86 percent of similar companies in the fatigue category.

"You can tell this is a problem carrier," said Henry Jasny, general counsel for the group Advocates for Highway and Auto Safety.

SkyExpress Inc. buses have been involved in four crashes, with one injury or fatality -- the motor carrier agency didn't specify which -- during the two-year period that ended May 20.

Its drivers have been cited for 17 unsafe-driving violations, including eight for speeding, since 2009. That gives it worse marks than nearly 63 percent of comparable transportation companies in the agency's unsafe-driving category, which is separate from driver fatigue.

SkyExpress also ranked worse than 99.7 percent of similar companies in driver fitness, with 24 violations, 14 of which were for using drivers who lack English-language skills.

"To drive any commercial vehicle in the United States, you have to have English proficiency," Jasny said. "You don't have to be fluent but you need to be able to communicate with passengers and law enforcement and understand signs on the highway."

The company runs 31 motor coaches with about 50 drivers. It offers service between New York and 13 cities in North Carolina, South Carolina, Georgia and Florida, and service between Washington, D.C., and two Virginia cities, according to its website.

Passenger Frances Lippette, 69, a retired New York schoolteacher who lives in Raleigh, uses SkyExpress about every six weeks to visit her daughter in New York.

She went to the ticket office to pick up her seat assignment for a bus scheduled to depart Tuesday night in New York, but the glass booth was dark.

She pays less than half the price of a name-brand bus company for the 8-hour ride.

It's "no worse than Greyhound," she said. "I've never seen a driver not alert."

Tuesday's accident came a few weeks after the motor carrier safety agency outlined new tour bus safety measures including making new vehicles have stronger roofs and windows.

Federal authorities say nearly 2,800 spot safety checks of passenger buses across the country from March 28 through April 6 resulted in about 10 percent of the vehicles or drivers being taken off the road.

But Sen. Sherrod Brown, sponsor of a bus safety bill in Congress, said recent deadly crashes demonstrate that the bus industry won't take essential steps to protect passengers' safety unless required by the government.

"How many deaths do we have to have before the bus companies are going to start saying, `Maybe we don't need more time. Maybe we should start doing something about this,"' the Ohio Democrat said.

Brown and Sen. Kay Bailey Hutchison, R-Texas, have been trying for three years to pass a bus safety bill that would require better training for drivers, seat belts and stronger bus roofs and windows. The SkyExpress bus had no passenger seat belts, only for the driver.

The bill was poised for Senate passage last year until Sen. Tom Coburn, R-Okla., placed a hold on it. With Congress closing in on adjournment, and other pressing legislation waiting to be voted on, the bill died. A Coburn spokesman said previously that the bill was costly and unnecessary.

A nearly identical bill was reintroduced earlier this year.

The federal Department of Transportation has proposed requiring buses to have seat belts and electronic on-board recorders to replace easily falsified paper records of driver hours. The proposals also would make it easier to revoke drivers' commercial licenses following violations.

The American Bus Association says the problem is limited to a small number of rogue operators and what's needed is tougher government enforcement of existing safety regulations.

"I question how a company like this is allowed to operate," the group's president, Pete Pantuso, said of SkyExpress.