Even the most violent collisions between current models rarely result in fires, according to automotive experts and statistics.

Authorities have not said whether they believe the young women died as a result of the impact or the fire. Autopsy results were not yet available, Ontario County sheriff’s Lt. Ronald O’Brien said Friday. He said he did not know about seat-belt use.

Both vehicles probably were traveling at or near the 55-mph speed limit, O’Brien said, though the exact speeds have not been reported publicly yet.

Burns, a Rochester Police Department retiree, said 2005 TrailBlazers contain “black box” data recorders that indicate speed, acceleration, braking, seat belt engagement and other data in the moments before the impact. Such modules, he said, are “very survivable.”

O’Brien said he did not know whether investigators had found the device.

The fire may be the most distinctive thing about the collision Tuesday night on Routes 5 and 20 in East Bloomfield, Ontario County. Ontario County Sheriff Philip Povero said Wednesday that the fuel lines ruptured on the TrailBlazer and the tractor-trailer, and sparks or hot metal likely ignited the fuel. He said witnesses described flames that reached 50 feet in the air.

Such fiery crashes have become almost rare because of major safety improvements.

In fact, only one-tenth of 1 percent of all crashes in 2005 that involved light trucks — the classification that includes SUVs — resulted in fires, according to the 2005 accident data report by the National Highway Traffic Safety Administration.

Fires occurred in fewer than 3 percent of all fatal crashes involving light trucks, the report indicated.

Modern vehicles are “much less prone to fire. The incidence of fatalities has gone dramatically down,” said Feaheny, a former Ford Motor Co. engineering vice president.

In the 1970s, Ford was accused of knowingly using an unsafe fuel tank in its Pinto models that could explode after relatively low-speed rear impacts.

After the resulting scandal and litigation, the auto industry completely revamped fire safety, Feaheny said. Gas tanks were moved to more protected parts of the vehicle, and made from impact-resistant plastics. Even simple things, such as putting tethers on gasoline caps so they wouldn’t be misplaced, made a difference, he said.

“There’s a zillion things like that they did. There was a real attention paid to it, and it’s been successful,” Feaheny said.

Crash test results

The National Highway Transportation Safety Board, which tests vehicles’ crash-worthiness, assigned three and four stars to the 2005 TrailBlazer for frontal impact, and five stars for side impact. The tests measure the risk of injury to drivers and passengers; five stars is the top rating.

Some similarly sized four-wheel-drive SUVs made in the same year, such as the Honda Pilot, Jeep Grand Cherokee and Toyota Highlander, got straight fives in front- and side-impact ratings. Other comparable SUVs, such as the Buick Rendezvous and Nissan Pathfinder, had ratings similar to the TrailBlazer. No mid-sized SUVS had lower ratings than the Chevy model.

The Insurance Institute for Highway Safety, an industry group, compiles “death rate” statistics for vehicles. It has not yet published statistics that include the 2005 TrailBlazers, spokesman Russ Rader said.

The 2003-04 TrailBlazers, included in the institute’s most recent statistical report in April, ranked relatively poorly, with 108 driver deaths per million vehicle-years. The average figure for mid-sized four-wheel-drive SUVs was 59. The worst death rating in that category, 127, went to the Mitsubishi Montero Sport. The best rating, 12, went to Toyota’s 4Runner.

Rader said factors beyond crash-worthiness affect the driver-death statistics. Demographics are a major factor — what sort of driver is likely to own a given vehicle, and how he or she is likely to drive it. Mini-vans, for example, tend to have low driver-death rates because they’re most often driven by cautious parents. Sports cars are owned by people who like to drive fast and are more likely to die in an accident, he said.

The vehicle involved in Tuesday’s accident was “demolished,” said O’Brien, of the Sheriff’s Office. “There was heavy front-end damage to both the tractor as well as the TrailBlazer.”

Records on the federal safety board’s Web site indicate the 2005 TrailBlazer has been subject to two recalls. A 2005 recall for windshields that were installed incorrectly affected about 12,000 TrailBlazers; the other, in 2006, involved possible airbag malfunctions on fewer than 500 vehicles.

The agency’s Web site lists no ongoing defect investigations involving the ‘05 model. The Web site also logs consumer complaints; by far the most common one involving that model year had to do with headlights that go dark or flicker for no apparent reason.