Investigators were looking into driver fatigue after a charter bus from Mexico veered off a Texas highway and flipped, killing one passenger and injuring dozens of others, authorities said. After the bus overturned Wednesday morning, a small pickup truck rammed into it, said Tom Vinger, spokesman for the Texas Department of Public Safety. The truck's driver was not injured. The bus had left Monterrey, Mexico, about 7:30 p.m. Tuesday and was headed to Houston when it crashed at around 4:15 a.m., Vinger said. "The investigation is centering on driver fatigue," Vinger said. "It looks like he ran off the road, way over-corrected then tipped over on the passenger side."