A school bus with more than 40 prekindergarten students returning from a field trip collided with a concrete truck and rolled over Friday in Texas, killing two people, authorities said. Texas Department of Public Safety Sgt. Deon Cockrell said another vehicle was also involved in the crash in the suburbs outside Austin. He did not know which vehicles the victims were in. The Hays County school district said the bus was involved in a "serious accident" while returning from a field trip to a zoo. Passengers on board included 44 students and 11 adults, it said in a statement.Cockrell said others who were injured were airlifted to hospitals, but he did not know how many.