One other comment about easements that nobody has brought up - When space is a concern and you simply have to make x degrees of turn in y inches, easements may still be a good idea, but you've got to pay the piper.
In other words, by giving yourself the luxury of including track at the entrance/exit to your curve that is broader than the average radius, you necessarily will include track in the middle of your curve that is tighter than it would have been without the easements. You have to balance your desire for easements against the corresponding reduction in your minimum radius to create the best looking/running curve you can in the space available. I don't think there is a formula for that situation. Some equipment may be more sensitive to the change in lateral acceleration, while other equipment may be more sensitive to the absolute minimum radius.
