I'm an 18 y/o, and in my family that has 4 teens (yeah, imagine that!) my oldest sibling had to pay for her own car, rego, insurance, etc.
So did my older brother.
As will I, and as will my younger brother.
It infuriates me to know that there are some kids that have parents that spoil them and buy them a car for 16th/18th/graduation presents. Not because i would love to have one for any of those three as a present, but here's what my brain thinks, and any teen with half a brain will think also:
"I know my parents will not buy me a car as they had not bought my older siblings a car. So i need to get a job, make money and buy it out of my own pocket. I'm responsible for rego, insurance, know the risks and have worked my arse off to get the 50 hours of driving time required! I am NOT going to lose this privilege."
To assist your teen, help them gather all the information they need. Help them realise how much a car costs to run.
Also, in Australia, i'm lucky to be living in a neighborhood which has plenty of public transport to all major places i would go to, so for me, it's a simple choice - spend money on a depreciating asset that will cause me to work for this priviledge, or use public transport (not out of laziness but fiscally) or if it's in 20-30 mins walking distance, walk it.