Shuttles or Seat in bus transfers (SIB) works on pre-established routes and schedules. A driver picks up travelers in different hotels and goes directly (without stopping) to the destination. Once there, the driver goes to the different hotels to leave the passengers. In this type of transportation you will be travelling  with other tourists, but, in spite of the inconvenience of having to wait until they gather all of the passengers and then leave them, the good thing is that these transfers are relatively low budget, and more practical and safe than to travel in a public bus.