The chartered bus that exploded near Dallas last month, killing 23 elderly Hurricane Rita evacuees from a long-term-care facility, had a defective brake, an illegal license plate and a driver -- charged yesterday with negligent homicide -- whose Mexican license wasn't valid in the United States, according to state and federal officials.

The operator of the bus, Global Limo Inc., had a low federal driver safety rating. A government investigation after the accident found 168 alleged violations involving the four other buses in Global Limo's fleet, and the federal Department of Transportation has since ordered the company's vehicles off the road.

Public safety experts and consumer advocates say the incident offers a cautionary tale about the charter bus industry, demonstrating how a prominent company such as Tysons Corner-based Sunrise Senior Living Inc., the largest assisted-living corporation in the United States, can end up relying on a small carrier with a spotty safety record.

With a patchwork of state and federal regulations, federal bus company ratings based on sometimes incomplete data and an often tangled web of vehicle ownership records, those experts say it's difficult for people or companies using charter buses to know if they are getting a well-maintained vehicle with a competent driver or one that's headed for trouble.

The fire and explosion on Interstate 45 have triggered four government investigations, three lawsuits and a promise by the assisted-living industry to draft bus-chartering guidelines for its members.

Sunrise had booked the bus through a middleman, the Chicago-based BusBank, which in turn contracted with Global. Finding a bus operator "can take days," the BusBank advertises on its Web site. "It's not simply a matter of who has a bus on a given day and how much it costs, it's about checking: The operator's safety record. . . . Are the buses well maintained?"

"The buses showed up. They looked safe," said Jamison Gosselin, a spokesman for Sunrise. The evacuation of the company's Brighton Gardens facility in Bellaire, Tex., near Houston, was made on short notice and came less than a month after it had successfully emptied its New Orleans facility during Hurricane Katrina.

Sunrise's top executives, including founder, chairman and chief executive Paul J. Klaassen, declined to be interviewed for this story.

Along with the brake problem, the bus had a complicated trail of ownership. Though registered in Oklahoma, it carried a Texas license plate that was supposed to be on another vehicle, according to the National Transportation Safety Board. The bus is owned by a Vancouver, British Columbia, company that had leased it to a Beltsville company, which had leased it to Global.

The driver had been stopped three times in the past seven months and cited for 11 violations, including speeding, according to the Texas Department of Public Safety. Yesterday, Juan Robles Gutierrez, a Mexican national who had been jailed on alleged immigration violations after the fire, was charged with negligent homicide by prosecutors who said he failed in his responsibility to ensure the safe operation of the bus. His Mexican license was invalid because he had been in the United States for more than 30 days.

"Most folks who charter just a couple of buses don't think about asking questions about the driver and bus company. But they should," said Joan B. Claybrook, president of Public Citizen, a Washington-based consumer advocacy group, and former head of the National Highway Traffic Safety Administration. "They should at least make sure the license of the driver is untainted. They should ask the owner of the bus company when the buses were last inspected."

Compared with automobiles, bus travel is relatively safe, with about half the fatality rate for every 100 million miles driven. In 2003, the most recent year for which government data are available, there were 57,672 bus crashes in the U.S., which resulted in 18,174 injuries and 40 deaths.

But the explosion in Texas was the third high-profile bus fire in the U.S. this year. Two low-fare buses traveling between New York and Boston caught fire, and though no one was injured, Massachusetts officials did beef up surprise inspections. Last year, a Disney Cruise Line bus was evacuated on a central Florida expressway before it burst into flames; no one was injured.

With Americans taking about 800 million bus trips each year, even industry officials feel there should be stricter oversight and more surprise inspections. The industry is governed primarily by the states, which oversee safety inspections; federal law requires interstate carriers to certify every 12 months that they have complied with regulations.

"We are in part a victim of our own success, the fact that we have been so safe," said Peter Pantuso, chief executive of the American Bus Association. "So the Department of Transportation has a tendency not to put as many people on the ground looking at the bus industry as we would like."

The cause of the bus fire in Texas has not been determined, though investigators are focusing on the right rear brakes, according to a local law enforcement official. Oxygen canisters used on the bus by some evacuees -- and also stored in the baggage compartment -- fueled the flames.

Along with the Dallas sheriff's department, three federal agencies -- the NTSB, the Department of Transportation's inspector general's office and the Federal Motor Carrier Safety Administration (FMCSA) -- are looking into the incident.

The FMCSA dispatched investigators to Global Limo a day after the explosion. Examining the company's other buses, it discovered 168 alleged violations that "were across the board in every category we regulate," said Robert Johnson, a spokesman for the DOT, which oversees the motor carrier safety administration. "The violations covered everything from recordkeeping to actual problems with equipment on the buses to drug testing to driver qualifications."

The decision to order the Pharr, Tex., carrier off the road was a "rare" and "rather unprecedented" move by the federal government, Johnson said.

An attorney for Global Limo, Mark A. Cooper, did not return phone calls seeking comment. Calls to the company's office indicate the phone line was out of service.

A day after the explosion, Global Limo released a statement saying, "Our prayers are with those affected by this loss." The company pledged to "continue to cooperate with the ongoing governmental investigation."

The owner of the BusBank, William R. Maulsby, declined through a company executive to be interviewed for what were described as "legal reasons."

The BusBank is a co-defendant with Sunrise and Global Limo in two lawsuits alleging negligence. One suit, filed by an 84-year-old woman who escaped from the bus, asserts that survivors "saw people burned to death as they struggled to get out of the bus and heard screams of both the living and the dying." A third lawsuit names only Global Limo.

Gosselin said Sunrise didn't ask, or really need to know, the name of the company the BusBank hired to evacuate its New Orleans or Bellaire residents.

"The BusBank guaranteed a lot of stuff," he said.

Charter bus customers can check the FMCSA's Web site for safety information on carriers. However, the information is often incomplete because some states don't update data in a timely manner.

Global Limo, for example, had an overall "satisfactory" rating at the time of last month's accident. But its driver safety rating was 97 on a scale of 1 to 100, with 100 being the worst. And the FMCSA's Web site also showed that four Global Limo drivers and three vehicles had been ordered "out of service" over the past two years. The DOT says it is examining why Global Limo was given a satisfactory rating.

The FMCSA says it has "temporarily restricted public access" to some bus and truck crash information "due to concerns about the timeliness, completeness and accuracy" of the data. "Public access to this information will resume once FMCSA is confident that the information provided by the States has improved," the agency's Web site says.

The Assisted Living Federation of America, a Fairfax-based trade group that includes Sunrise among its members, meanwhile, is trying to develop policies to help its members avoid another tragedy.

"We're going to look at best practices to give our members so that when they enter into their contracts [with bus operators] they can verify that the services they are getting are the same as what was represented," said Paul J. Williams, a federation official. "Going forward, the bottom line is: How can we do due diligence in order to prevent something like this from happening again?"

Researcher Bobbye Pratt and staff writer Mark Chediak contributed to this report.

Emergency crews investigate the scene where a bus carrying elderly Hurricane Rita evacuees exploded on Interstate 45 near Dallas. The explosion and fire killed 23.