The NYT reports:
The Environmental Protection Agency has revised its alternative-fuel conversion regulations for light and heavy-duty vehicles, making it easier for manufacturers to sell conversions that are compliant with clean-air laws. The 186-page ruling provides an exemption from a Clean Air Act prohibition against tampering when converting an engine to run on alternative fuel.
In the past, a manufacturer of alternative-fuel conversion systems was required to certify its products in the same manner that a vehicle manufacturer certified its vehicles — an expensive and difficult process. The new regulations provide a way to comply with clean-air standards through streamlined testing.
In essence, the rule change creates a graded compliance structure, depending on the age of the converted vehicle, making it easier to retrofit older vehicles. Read all about it at the EPA’s website.