On Pioneer Electronics site there is a pdf document about DVD-R DL Specifications. Pioneer has created a DVD-R DL that as the same characteristics of DVD-Rom DL. The DVD-R DL jitter error is the same of DVD-Rom, also the Track Pitch is the same, the Reflectivity is the same and if you see Target Specifications of Dual Layer Disc for DVD-R, and precisely near to Writing path, you see that it's write Parallel and Opposite.
Pioneer has proposed the Specifications to DVD Forum that approved all. In fact on DVD Forum site, near to all DVD-R DL specifications is always write Approved.
So, the DVD-R DL support both Track Path. (Parallel Track Path) - (Opposite Track Path). All burning programs have Opposite as defautl Track Path. For write in Parallel you must use a program that allow you to choose Parallel Track Path. Gear Pro Mastering 7.00 have this options and allows to write in Parallel and Opposite (DVD Settings), but this program doesn't support the write on DVD-R DL yet, but it only support DVD+R DL that can be write only in Opposite.
I send an e-mail to Alcohol 120% creators for insert the write in Parallel and Opposite as Options in the next version of program.
This is the link for DVD-R DL Specifications: DVD-R DL Specifications