Doc: "It's perfect! A nice long run that goes clear across the bridge over the ravine. You know, over near that Hilldale Housing Development?"
Marty: "Right, Doc. But according to this map, there is no bridge. Well, Doc, we can scratch that idea. I mean, we can't wait around a year and a half for this thing to get finished."
Doc: "Marty, it's perfect! You're just not thinking fourth dimensionally."
Marty: "Right, right. I have a real problem with that."
Doc: "Don't you see? The bridge will exist in 1985. It's safe and still in use. Therefore as long as we get the DeLorean up to 88 miles an hour before we hit the edge of the ravine, we'll instantaneously arrive at a point in time where the bridge is completed. We'll have track under us and coast safely across the ravine."
Marty: "What about the locomotive?"
Doc: "It'll be a spectacular wreck. Too bad no one will be around to see it."