There are 2 methods in which you can use to report these costs. The first is Actual Expenses. Under this method you would record all of the costs related to your travel away from home in connection with the rental property. These expenses should be recorded and backed up with receipts in accordance with IRS Publication 463 Chapter 5. Certain software apps are available via iPod, Quick Books, Mint, and others; however you still must have a tangible document to back up your deductions. You are required to report this either on your Schedule C or Schedule E with supporting schedules attached. If you have multiple properties, your expenses should be allocated to each property in which the costs are incurred. Remember to not include any personal use or any other use except that which is related to the property.
The second method is the Mileage method, under this method you want only use your actual mileage traveled to deduct. For example, if you traveled 1200 miles during 2012, you would use the current standard mileage rate of $0.555 per mile according to current tax rates.
Use of local transportation such as Zip Cars, Metro bus service, and auto rentals must have a direct correlation to the property and must have documentation to support this. If using public transportation, it is recommended that you have a separate fare card and a separate business account for rental cars and Zip cars to show that the use is solely business related.
For more information please refer to IRS Publication 527.