Perhaps the simplest and most effective route is to establish two separate LLC's for each company. The reason being is that the LLC is an asset protection vehicle in and of itself, negating the need very likely for a trust (which is more typically used for family and other personal assets). Also, having only one LLC is ill advised due to the unique liabilities, revenue streams, and other features associated with each business. You would not want to co-mingle them. For example, if the taxi company is doing great and suddenly you are sued for a death associated with the medical transport company, the taxi company's revenue stream would be up for grab's by the plaintiff in that lawsuit. Of course, you should consult in person with a local business attorney to get a better handle on these concepts and plot out the best course for you.
I hope this helps.
Disclaimer: This answer is for informational purposes only and does not constitute general or specific legal advice, nor create an attorney client relationship.
I agree with the answer above. There should be 2 separate and distinct LLC's with 2 separate EINs, bank accounts, and sets of books, and you should consult with an attorney in your state to discuss and handle for you/