I would, without giving it a second thought, visually check the surrounding area, stop, assess the injuries, and give what immediate first aid I could.
Then, if it appeared that moving the person would not further injure them, I'd put them in my vehicle and drive to the first town I could find.
If I felt moving the person was out of the question, I'd drive to the nearest home or town, gas station, etc., and place a call for emergency response. Before departing the scene, I'd reset my trip mileage to zero and determine the direction I would be traveling in so I could give first responders an accurate location of where the injured person could be found.