After Jeffrey eats at at the Pickwell's, the children follow him outside and find him running where?

From the text:

There he was, passing Red Hill, a book in his hand. He was running, passing the spear field now, and the Pickwell kids had to blink and squint and shade their eyes to make sure they were seeing right -- because the kid wasn't running the cinders alongside the tracks, or the wooden ties. No, he was running - running -- where the Pickwells themselves, where every other kid, had only ever walked -- on the steel rail itself!