Alia here's some

It sounds like your DS thinks this is the best way to do it, for him anyway. I imagine it is a huge wrench for him too.
As peeps have said he may change his mind as he sees the pile of stuff growing and the snapchats of his mates setting off in cars but he may not.
If he doesn't, then presumably he'll need a lift to the station? In which case that will be your waving off moment, whether in the car park or the station. You can pop an emergency treat package in the post to arrive early on.
I sent DD the odd postcard with a pic such as of her with our dogs (postcards online?) and one with this on which is a bit girly and also wrong sentiment for your boy.
My DD did not want parents hanging around or even worse talking to flat mates or their parents. We had a very firm time to go stare. As I walked down the stairs the tug in my chest was painful. I was ok back at home until I went into her room to shut a window and lots of her stuff was gone. Sat on her bed and cried.
For the first week or so I had a lump in my chest and wrestled with not knowing how she was. I think we are biologically programmed to look for members of our tribe if we don't know where they are and certainly for our child. The trouble is we are always playing catch up as parents and just a little bit behind the young adults we now have.
When I went to uni, aeons ago, my mum dropped me off, gave me a phone card and smiled and waved. She told me a few years ago that she cried for the 2 hour drive home. I had no idea. We are still close. She is a wonderful grandmother.
My DD2 is moving to a new city and lodgings next week to begin an apprenticeship at just 17. She is worried about loads of things, particularly how she will manage financially. DD1 a student, thinks this is funny as DD2 will have a salary and no student debt. Anyway, no matter how I try to help DD2 with her worries, she is still worried. I think the only thing that will help is to just do it. So even if DS told you every single worry, there is only so much you can do to help.
Sorry. Very long. DD1 went to uni at 19. DD2 going at 17 has blindsided me so I am with you