Commuting expenses are never deductible, before or after tax reform, for W-2 workers or self-employed.
If you are self-employed, you can deduct your work mileage whether you use your own car or a rental. You can't use the standard mileage rate for a car you don't own, so you would have to use the actual expense method, that would include the rental fees and fuel.
The difference between deductible work mileage and non-deductible commuting mileage is described in chapter 4 of IRS publication 463.
https://www.irs.gov/forms-pubs/about-publication-463
