My 4 year old went missing yesterday for over 10 minutes and was found in the main road

Hello everyone I’m kind of new here, my 4 year old was diagnosed was autism late last year, he’s non verbal and has no sense of danger, he’s also had 3 open heart surgeries and has had hearing loss so has grommets fitted but still fails his hearing tests although we are not sure if it’s not down to his autism and loosing interest too quickly in the hearing test. Anyways, yesterday I was in my front garden which has no fence as we live in a very quiet cul de sac and none of the houses have a fence here, however my child is usually fine in the garden and has never ran off before, I was stood right by him chatting to my family Member who had came to see us for my other child’s birthday so my other child who is now 3 was also out there with us playing right beside us, it all seamed ok. Then a neighbour of mine came back from a walk at the shop and he thought he had seen my child at the very top of the cul de sac heading through the cut into the next street, I quickly glanced around and realised my 4 year old wasn’t with us anymore, I ran upto the top where he was seen but he wasn’t there, my family member came with me and I left my 3 year old with my oldest child in the house, my family member went one way and I went another and we stayed on the phone while running around so we would know if either of us found him, I asked dog walkers and people working on houses and gardens if they had seen a small boy in his pjs, nobody had seen him where I was and I felt he didn’t go down this way, up the other way is a field and a dog walk which leads to a bridge that crosses the busy motorway and the railings on the bridge are around 4ft tall and my son is always climbing over fences and over the decking handrails, it seamed like forever this was going on, I said to my family member at what point do I call the police? He said give it a couple of more minutes then we will have too, I ran out of a side street and onto the side of a main road when I looked up to the next side street and seen my child run out and into the middle of the main road, he was quite a distance away and I was so out of breath already and I also have a heart condition myself and knew I couldn’t make it much further but I had too, I ran to him calling his name and he began running the other way but down the middle of the main road right on the bend in the road I was so worried a car or van would come speeding around that bend at any second and I was running as fast as I could to get to him, I screamed his name at this point and he turned around and ran to me. We carried him back to the house and checked him over he seamed fine and of course has no idea of what he’s done. I’m still quite shaken by this even though it was yesterday, Iv never had this happen before not even with any of my children. It was an awful experience and I worried that because he doesn’t talk and has no sense of danger at all that nobody would know who he was or where he lived not even what his name is. I’m so glad my neighbour seen him as I don’t know when I would have noticed he wasn’t there although I would have assumed he had went back into the house rather than run off. So all in all he was missing just over 10mins and found 4 streets away from where he lives and if I hadn’t of ran out of the side street when I did and he didn’t run out of the next side street when he did I wouldn’t have found him at that moment. Has anyone else had a similar experience?