The trouble ehre is that mine (I am ignoring teh Sn ones and just eman the NT ones LOL) are the only kids in our road. So we don;t ahve that all-in-it-together thing DH and I had as kids.
And wrt to traffic most kids commute in from quite a distance, so unwalkable, the school tried to set up a walking bus from outskirts but aprents said no (don't knwo why though, may well have been genuine reason but we live closer so I never paid it much attention).
It really does need to be a kid and area by area basis. Besides yes we were allowed out but equally I remember what we got up to- playing on building sites, canal locks, on the dockside. An absolute miracle nobody died tbh, and Mum sauys when she was a child it was accepted a few kids would die whilst playing out: that shook me a little. I don't think I could accept that.
DS2 is 9 now and if he had a mate to walk with I would allow him the (busy with other families) walk to school, and he will certainly have to do it next year if DS4 goes to a different school. HAd ds1 been NT and they could have walked together- who knows?