Keep in mind that you will not keep 4-wheelers out if they want in ... especially when you are not there so making the temp-drive removable is not as important as having a way for YOU to get into your property.
I would opt for the RR ties if I were doing it. They can definitely hold the weight (we use them for this very thing) I would also just leave them there till I installed the permanent drive.
If you want to keep cars from being able to have easy access, install the RR ties part way down the slope. The tractor will not have any problem with that but a car would never make it.
If needed, wait till DOT has approved the road before you build a temp access.