There's a stiff in the driver's seat. Can I drive the vehicle?

In the demo version of OFP, you cannot drive a vehicle if there's a dead person behind the wheel. However in the full version of OFP, all you have to do is approach the vehicle and select GET IN AS DRIVER, as you would for any unoccupied vehicle. In this case, the cadaver will be tossed out on the ground alongside the vehicle.