A single-vehicle fatal accident is under investigation in La Porte City. Authorities said a white box truck was discovered on its side resting against a tree in the 800 block of Commercial Street (U.S. Highway 218) on the southern edge of the city just after 5:30 AM Wednesday. According to La Porte City police, the first officer to arrive at the scene found the driver –- and lone occupant -- unresponsive inside the vehicle. Officials said the driver died after being extricated from the vehicle by La Porte City firefighters. Authorities did not immediately identify the victim. In a press release, La Porte City police said their initial investigation indicates the truck was going north when the driver went off the pavement and lost control of vehicle. The vehicle overturned, then struck the tree. La Porte City police and firefighters were assisted by Black Hawk County sheriff's deputies, Waterloo Fire Rescue and the Iowa Department of Motor Vehicle Enforcement.