Are you looking for transport from one facility to another? For example from one hospital to a higher level of care hospital? If so, you will need critical care trucks and EMS helicopters for this. If you're looking for regular transport from things like falls or vehicle accidents, there is a matrix set up that will spawn calls based on the amount of buildings you have, not vehicles you have.
Not all interfacility transfers/transports required Critical Care or Helicopter. In fact some are even BLS. and most will simply take an ALS unit. I believe the volume of calls is based on some logorythem related to the number of Hospitals and Clinics and they only generate sporadically. I have never had more than 10 at one time, but I have a setup that includes hospitals and clinics all across the state of Florida, and parts of AL, GA, and Miss on the US version