When does an 'unfamiliar' journey become 'familiar'?

My 16yo son has autism. He gets the bus to his dads each week, and has done for nearly 4 years, but is still not able to do this journey alone.
But, he can now get the bus to school himself, but this has taken over 4 years of daily practice with someone with him for him to get to this point, and he still has occasional issues if there are changes e.g. bus cancelled or diverted (he continues just waiting, so I have to pick him up), or if he has to interact e.g. got kicked off bus for being 'aggressive' when he had to speak to driver, even though he didn't realise he was coming across as aggressive (he uses bus pass and headphones to avoid interaction).
I am wondering if you think descriptor 'f' 'Cannot follow the route of a familiar journey without another person' should apply?

Hi BIS,
Thank you for your advice it has really helped. He doesn't really go anywhere else regularly, and any other trips e.g. to GP, then I have to take him.
Thank you again