If your curve is flat you can simply change the curve type to 2D to ignore the tilt for each control point:
If it is 3D and you want to keep it that way, you need to reset the tilt of each control point that isn't set to 0 degrees:
EDIT: You can also try setting the Twist Method to Z-Up.
EDIT 2 (after seeing the blend file):
Start with applying all transform on the curve (CTRL + A > All Transforms), then set the Twist Method on the curve to Z-Up. Then you'll have to tweak the Z-rotation of the locomotive to make it line up with the track, something like -28 degrees seemed to do the trick for me.