Six Foot Rail Regression BRT

Sorry, I don't clearly understand what you want to do and what source data are to be regressed.

Instead of creating a proposed Centerline to regress, i want to create a proposed six foot rail and regress this as this would give a true slue report and be able to calculate an accurate design six foot dimension.

If you've got the existing CL as surveyed points (or left & right rails to convert to CL) and if you want to do a regression from this data to directly create the six foot, you can edit the regression points to enter the required offset (six foot + half gauge)

If you've got the existing CL as surveyed points (or left & right rails to convert to CL) and if you want to do a regression from this data to directly create the six foot, you can edit the regression points to enter the required offset (six foot + half gauge)