The IRS has not yet released guidance concerning Section 179 and Bonus Depreciation as it relates to vehicles for the year 2013. The guidance will be published in the Internal Revenue Bulletin sometime after April 15th. So be patient, and check back here often for the release date.
There are a number of qualifications for vehicles, all with varying tax treatment. Please refer to page 6 of these Instructions for Form 2106 to read the exact IRS language.