Transportation Secretary Sean Duffy announced his department is investigating last week’s deadly motor vehicle crash in Florida, in which Harjinder Singh, an undocumented immigrant, made an illegal U-turn in a semi-truck on the Florida Turnpike and killed three people in an oncoming minivan.

Preliminary results of the Federal Motor Carrier Safety Administration investigation show Singh, the driver of the 18-wheeler, failed an English language proficiency exam. He answered two of 12 questions correctly and identified one out of four road signs.