How do Amtrak trains running diesel electrics (e.g. P42 Genesis) maintain a more-or-less constant 79mph (or whatever the track speed is)? Is there some form of electronic cruise control? It seems that the engineer constantly moving throttle notches to hold a steady speed would not be nearly precise enough to hold the steady speeds that I see on my GPS or on the track recordings. On a related question, when accelerating from a stop on dry rail to track speed does the engineer gradually and sequentially increase run positions or can they skip notches?