Full-size passenger vans pose a greater risk of rolling over than smaller vans when fully loaded, federal safety regulators said in a new study raising more concerns about the safety of light trucks. The study by National Highway Traffic Safety Administration (NHTSA) researchers -- conducted in response to several high-profile accidents -- sparked a major debate inside the agency about how to interpret the results and whether they should be released. The study was completed last July but the findings were only presented on March 5 at the Society of Automotive Engineers’ 2001 World Congress. NHTSA officials didn’t offer any solutions to the safety issues raised by the study. NHTSA researchers said it was clear that passenger vans that can carry up to 15 passengers were more likely to be involved in rollover and fatal accidents than smaller vans or minivans. Further, it appeared that the rollover dangers increased when the vans were carrying full loads. The vans were 17 percent more likely to be involved in a rollover crash than smaller vans when they were carrying between one and four passengers. When carrying 15 passengers, it went up to 35 percent. For 16 or more passengers, it was 70 percent. The safety agency was able to show through road tests that vehicles were more likely to tip over in the face of specific driving maneuvers like sharp turns. The road tests also showed that the vehicles, when fully loaded, were a lot more difficult to handle. That raises safety issues because no special training is required to operate the vehicles, such as the commercial driver’s license that truck, limousine or taxi drivers have to obtain. Automakers had little to say about the NHTSA presentation, saying they haven’t had a chance to review the findings. But they stood behind their large passenger vans as safe, reliable and economical transportation for groups.