I can tell you about these 2 big curves which I had seen during my Oct, 2011 HWH-KLK Mail Journey. One curve was at Allahabad Outer and I could see my train's WAP-7 taking a left turn on the curve after crossing the Signal Post which denoted the change of signal system from Automatic to Manual Mode. I have also seen this curve after Kanpur Central which covers the stretch between Kanpur Central and Govindpuri, where again I could see my entire train from my coach till the last SLR Coach ... Gee :-D