a friend of mine's son has always cycled to GS from the middle of Cheltenham to Gloucester. This involves going along the A40 which is a brute of a dual carriageway. I wince to think of it. Since Y7 he's gone (April child). Not helpful, I know, because it fills me with horror but it's all that her circs permit and the boy's been fine
So it CAN be done, however horrifying the thought. (and sorry, to all the gung-ho-ers, but it IS horrifying! all the cliches of white van man texting etc . ..)
Could he stay on at school, do his homework there (ours has homework "clubs") and be picked up later by you?
Or go to a library or somewhere safe to be picked up, again, later.
Can you play it by ear by doing practice walks on a Saturday, just to familiarise him.
I do understand entirely what you mean by the loneliness thing and 15 mins seeming quite a long walk. To have to start telling him to have his phone switched on and in his pocket ready to use is to start raising alarm bells. Someone else, surely, must have this problem??
Maybe cultivating a shared system with the other children is the most practical way. Even tho the children aren't good friends, the mothers will understand the situation.