I have a 65 mile commute to my primary place of employment. From this practice location, I also concurrently conduct a second, completely independent business. The income I receive from these is from two different sources. Can I deduct my mileage against this second business? Both jobs must be performed at the primary practice location (i.e., the second business cannot be conducted at my home, etc.)
Thank you.

From your email, it would appear to me that whether you are going to work for one or the other of the two enterprises, your travel is a "commute" and would not be deductible. Travel between two jobs would generally be deductible, but since both your jobs are at the same physical location, you don't have any travel between jobs.

Zip Code: 43085

do some documented work for your primary job (in case you are audited) - paperwork etc.... - before leaving to go to your "1st" location. The you are no longer commuting to work but traveling between work locations..... Or if you have an independent entity for your second job you may be able to have all the vehicle through that one depending on your "corporate" structure.

of course consult with your local trustworthy tax professional/planner.