How is it decided what insurance company is billed first?
It depends on whether you have Medical Pay coverage on your auto insurance, and what your health insurance coverage benefits are. If your health insurance has restrictions, such as calendar year maximums, limitations on the visits, etc., you may choose your auto insurance to be primary so that your health insurance is available for other injuries. Also, most health insurance plans will have you complete multiple subrogation forms, accident details, etc. so it may be easier to use your auto insurance.