My buddy's autistic son was a 'runner' when he was about four or five. He would invariably go about a block to where a stream passes under a stone bridge along a semi-busy street...to watch the water.
Luckily, he grew out of the impulse to run.
Luckily, my son has never been a runner. But he LOVES to watch running water. I think most autistic children do, which can be very dangerous.