Here's a couple of pics of a roller jig for routing the outside slot:


The out side edge of the track is cut using a regular radius, but since the rollers are spread out, the router will gradually move inward, creating somewhat of an elliptical effect. When the trailing roller meets the curve, the router will cut parallel to the outer edge until the leading roller gets to the next straight.
Here's a pin jig for routing the remaining slots (always work from the outside in):

The pins in this jig are relatively close together to maintain a consistent lane spacing. If the pins are spread further apart, each subsequent lane will gain more of an elliptical shape and will also gain more lane spacing in the middle of the turn.
I hope this helps.