Hmmm, hiding might not work. I did the same to DD, I ended up following her at a distance. She walked nearly halfway across Knox City (pushing her dolly pram) and was about the board the escalator when I had to grab her.

She didn't look back ONCE! Was having a lovely old time, didn't get scared at all...

However, if he continues to take off I'd get a backpack strap outfit for him. I know you don't like them much but running into traffic is too dangerous to risk xoxoxo