To amend the Clean Air Act to clarify that certain conversions of engines and motor vehicles from conventional fuels to clean alternative fuels will not require additional certifications, and for other purposes.

Amends the Clean Air Act to authorize the Administrator of the Environmental Protection Agency (EPA) to approve a combination of conversions to a clean alternative fuel into a single test group, which would normally not be eligible to be in a single test group, if the manufacturer of motor vehicle or engine conversions provides: (1) substantial evidence that all the conversions in the larger grouping will have similar levels of emissions; (2) evidence of equivalent component durability over the vehicle's or engine's useful life; (3) evidence that the groups will result in sufficient in-use verification program data, appropriate tracking in use, and clear liability for the EPA's recall program; and (4) a statement that all vehicles within a test group are certified to the most stringent standards applicable to any vehicle within the test group.

Establishes the Advancing Alternative Fuels Revolving Loan Fund. Directs the Administrator to use amounts in the Fund to provide loans to eligible local governments to finance purchases of authorized equipment to enable public vehicle fleets to operate on alternative fuels.