SAO PAULO, brazil – The cars roll endlessly off the local assembly lines of the industry's biggest automakers, more than 10,000 a day, into the eager hands of Brazil's new middle class. The shiny new Fords, Fiats, and Chevrolets tell the tale of an economy in full bloom that now boasts the fourth largest auto market in the world.

What happens once those vehicles hit the streets, however, is shaping up as a national tragedy, experts say, with thousands of Brazilians dying every year in auto accidents that in many cases shouldn't be fatal.

The culprits are the cars themselves, produced with weaker welds, scant safety features and inferior materials compared with similar models manufactured for U.S. and European consumers, say experts and engineers inside the industry. Four of Brazil's five bestselling cars failed their independent crash tests.

Unsafe cars, coupled with the South American nation's often dangerous driving conditions, have resulted in a Brazilian death rate from passenger car crashes that is nearly four times that of the United States, according to an Associated Press analysis of Brazilian Health Ministry data on deaths compared to the size of each country's car fleet. In fact, the two countries are moving in opposite directions on ­survival rates — the United States recorded 40 percent fewer fatalities from car wrecks in 2010 compared with a decade before. In Brazil, the number killed rose 72 percent, according to the latest available data.

Dirceu Alves, of Abramet, a Brazilian association of doctors specializing in treating traffic accident victims, said poorly built cars take an unnecessary toll. "The gravity of the injuries arriving at the hospitals is just ugly," he said, "injuries that should not be occurring."

Automakers in Brazil say their cars meet the nation's safety laws. Some said they build even tougher cars for the country because of its poorly maintained roadways. They reject notions that cost-cutting in production leads to fatalities.

But the country's few safety activists perceive a deadly double standard, with automakers earning more money from selling cars that offer drivers fewer safeguards — a worrisome gap for new middle-class households, whose surging spending power has outpaced consumer protections taken for granted in more developed countries. The problem extends beyond Brazil, with economic forecasts showing the majority of global growth in auto sales taking place in emerging-market nations as the world's auto fleet doubles to 1.5 billion by 2020.

"Entry-level cars in Brazil are incredibly dangerous, it can't be denied. The death rate from accidents is far too high," said Maria Ines Dolci, coordinator of the consumer defense group Proteste. "The manufacturers do this because the cars are a little cheaper to make and the demands of the Brazilian consumers are less."

Manufacturers earn a 10 percent profit on Brazilian-made cars, compared with 3 percent in the U.S. and a global average of 5 percent, according to IHS Automotive, an industry consulting firm. Only next year will laws require frontal air bags and anti-lock braking systems on all cars, safety features that have been standard in industrial countries for years.