I based my 60% of the radius on several charts by several authors on the subject, including John Armstrong's "Track Planning for Realistic Operations." I averaged out the various recommendations and 60% of r came out pretty close to all of them. That would be 10.8" easement for 18" radius curves. Looking back at the video, I obviously had a brain fart which I totally missed. You are right, is should be 60%r/2 each side of the beginning of the circular curve. I clearly have to fix that. Thanks for catching my mistake.