My car accident victim is a healthy and physically fit 15-year-old boy, around 5'8" and weighs about 140 pounds. He is standing at the side of a road where the speed limit is 35mph, when he is hit by a car (a 1996 Ford Aspire). The driver had been sleepdriving and wakes up in time to swerve and avoid hitting one of the trees on the side of the road, but the boy isn't as lucky.
The thing about the boy is that he's an alien, with grey skin and horns, so taking him to a hospital is not an option and would drag the plot places I don't want to go. I need him to survive the accident with minor injuries that can be treated at home but will leave him incapacitated for two-three weeks.