My guess, that no one had dived into water. They probably took bridge down in winter, when river was covered by ice. And got track with crane there. Then just d

My guess, that no one had dived into water. They probably took bridge down in winter, when river was covered by ice. And got track with crane there. Then just drove away by the river. It explains why they preferred bridge over rails. Rails hard to move to a place where track could go. You'd need some type of cart that moves by the rails. While frozen river is like a road. There could be a lot of snow on the ice, but I believe it could be managed somehow.