Simple rules for model railroad track plan design

* The siding always curves away from the main on most turnouts. This is so high speed trains don't derail. You can make the turn at slower speeds if you are taking the siding because you are getting ready to stop anyway.
* The spur is on the opposite side of the main line than the siding, so that you can switch the spur without blocking the main with the rest of your train, there by allowing other trains to pass. It also allows you to pull cars off of either end of the train.

* The yard lead should be longer than the longest track in the yard, so you can work the yard without going on the main. If it is too short you will have congestion problems.