heres an update, thanks all for your help. In the end I did something similar to what Anis surgested...

Between red and blue I blended the shape together.






I am a little disaponted that getting the basic shape took me so long, all of my problems were getting the curve between red and blue the way it was on the real train. It would have been great if there was some controls to handle the amount of tangancy/buldge at the start and end of the blend shape. I found that because the amout of blend was tight at the top and more loose at the bottom that getting it working correctly was a real pain