I first have to say that I am normally very aware of my surroundings when I am driving. I have never not spotted a stray dog on the side of the road before. I have managed to stop for plenty a bird and the odd cat or echidna well before I reached them.
I was driving home from work along a 2-lane 60kph road. It's a narrow road, but a busy one in peak hour. First I spot an ACD standing in the middle of my lane. He was impossible to miss, so I slowed down well before I reached him, holding my breath because he was facing the oncoming traffic. But he decided to not risk the crossing and turned back. Not even 100m further this old, slightly overweight GRD seems to come out of nowhere and by the time I spot him he is already in the middle of the road. I hit the brake but I immediately realised there's not enough time to stop. Thank dog the dog stopped dead when he heard my car close to him! But I was pretty shaken.
Swore the rest of the way home about people not locking up their dogs when they live near a busy road. Though who knows how he got out. I think I was also just very annoyed with myself for not seeing him in time. Maybe he blended in with the late afternoon light.