A Utah State University van that crashed after a tire blew out, killing eight students and an instructor was traveling over the 75 mph (120 kph) speed limit, a Highway Patrol trooper said.
The university, meanwhile, began inspecting its 50-van fleet and said it may stop using the top-heavy vehicles that sit high on their axles and have narrow tires.
Another of the university's 15-passenger vans rolled in 2001 near Laramie, Wyoming, tossing around six volleyball players but leaving them without serious injury.
The National Highway Traffic Safety Administration has issued four warnings since 2001 about the safety hazards of 15-passenger vans.
Trooper Jeff Nigbur said speed was a factor when the van overtook another vehicle Monday on a northern Utah highway before blowing its left rear tire. "They were definitely going over the posted speed limit" of 75 mph (120 kph), he said Tuesday.
None of the 11 occupants of the crushed Dodge van was wearing a safety belt, violating a school regulation, and all were ejected from the vehicle as it rolled over, according to a preliminary accident report from the Highway Patrol.
The van was carrying agriculture students on a field trip. Two surviving students were listed in critical but stable condition at Ogden hospitals Tuesday night, reports the AP.