One way transfers from the end point (Ketetahi) to the start of the Crossing (Mangatepopo). Free, secure all day parking.
This is the popular hassle free and cheapest option if you have your own car.
You will do the 6-8 hour hike back to your car in the car park which is located a short walk from the end of the Tongariro Crossing. No need for afternoon shuttle transfers.

Bookings:

DOC require all visitors to book/notify in advance, (free of charge) if you are walking the TAC. Head to the DOC website for more information and to complete the form.
This needs to be done prior to departure and preferably before you book a shuttle. You will need to show proof to the driver.