General   (General discussion, talk about anything.)

If the train I travelled on between Chicago and NY was single decker as opposed to double because tunnels could not or it was too disruptive to alter them does that not say anything. On the double decker I don’t remember any bridges crossing the line other than Gathurst viaduct motorway type as we left Seattle.
On the other hand the London cross rail tube line has woven its way successfully amongst underground obstacles of every type including historic buildings foundations.