That's a difficult question to answer as California EMSA does not publish this data (http://www.emsa.ca.gov/data_inf/data_inf.asp). There are some national statistics available...
That's an excellent service business to have. Many senior citizens need transportation to and from medical appoinments. A few things you'll need to look into may include: business liability insurance...
Medicaid will cover transportation that's necessary because of the patient's condition, to/from a source of medical care (i.e., a service for which Medicaid would make payment).