A spectacular rollover crash that killed at least six members of a New York church has renewed questions about the stability of 15-passenger vans — which studies show become more dangerous when used. as intended. to transport large numbers of people.

The 14 parishioners from the Joy Fellowship Church of Bronx, N.Y., were traveling on the New York State Thruway to visit a sister church in Albany when the right rear tire of their 1997 Ford van blew out. The vehicle careened into the median and rolled three to four times, ejecting seven people, emergency crews told The New York Times. Among those killed Saturday were the pastor, Titus McGhie, church bishop Simon White, and his wife Zelda White. The eight survivors of the crash were seriously injured.

In 2001, the National Highway Traffic Safety Administration issued an unusual warning to owners of 15-passenger vans, which are often used to transport church groups and sports teams. The agency said the vans should not be fully loaded, because research had shown their stability declines markedly with 10 or more people aboard. The advisory highlighted a basic paradox of the vehicles, which are marketed as spacious carriers of people and cargo yet become tipsier under heavier loads — a fact little known to consumers.

The reason fully loaded vans are more dangerous is that passengers ride above the center of gravity, so that each additional occupant makes the vehicle more top-heavy and less stable — raising the risk that a tire failure or abrupt steering maneuver will cause a van to tip over. The same is true for other people-haulers — such as smaller passenger vans — but NHTSA research showed that the pattern with the 15-seaters was more profound.

NHTSA’s website continues to warn of the “significant increase in rollover risk when the van is fully loaded with drivers and passengers.” The addition of electronic stability control systems to newer vans has reduced the rollover risk, the agency said, but “models produced prior to 2004 likely do not have this crash protection.”

Owners should make sure tires are in good condition and properly inflated, and that drivers are trained to operate the vans, according to NHTSA. Seat belt use is also critical, as the death rate in single-vehicle crashes of 15 passenger vans is about three times higher for unrestrained passengers as for belted ones, the agency says.

Reports of Saturday’s accident suggest that many of the van’s occupants were not wearing seat belts.

In a statement provided to FairWarning, Ford safety communication manager Wes Sherwood said, “Preliminary reports indicate this accident was caused by a badly maintained tire and that most of the vehicle occupants were not wearing their safety belts. At Ford, the safety of our customers is our number one priority. Government research shows that 15-passenger vans are safest when properly maintained, driven at safe speeds by experienced drivers and when occupants wear their safety belts.”