Once more, let's go over the entire plan and layout. I apologize for the crudity of this...

Doc: Once more, let's go over the entire plan and layout. I apologize for the crudity of this model, but I just... Marty McFly: Yeah, I know, Doc. It's not to scale. It's okay, Doc. Doc: All right. Tomorrow night - Sunday - we'll load the DeLorean onto the tracks here on the spur, right by the old abandoned silver mine. The switch track is where the spur runs off the main line three miles out to Clayton... Shonash Ravine. The train leaves the station at 8:00 Monday morning. We'll stop it here, uncouple the cars from the tender, throw the switch track and then we'll hijack... *borrow* the locomotive and use it to push the time machine. According to my calculations, we'll reach 88 miles per hour just before we hit the edge of the ravine. At which point, we'll be instantaneously transported back to 1985 and coast safely across the completed bridge. Marty McFly: What does this mean? "Point of no return"? Doc: That's our fail-safe point. Up until there, we still have enough time to stop the locomotive before it plunges into the ravine. But once we pass this windmill, it's the future or bust.