[Steve A]

Intrigued, why figure of eight if it is just for test track? It adds bridge or x over and only usually needed to make two lanes equal length.
Understand you will need to test car on RH and LH corners, but should you consider a "S" bend, or nest two corners together to achieve RH and LH corners without figure of eight? Just my thoughts having made a small routed Top Gear track as a test track and found that the cross over was most difficult bit.
Steve