the net present value of the credits over time.
If a FEL is above the applicable emission standard, then the engine family is generating negative credits. Conversely, if the FEL is below the applicable emission standard then the engine family is generating positive credits. After the negative and positive credits are added up across the manufacturer's product line, the manufacturer must have a net positive or zero emission credit balance.
Nine-year phase-in: The applicable emission standards are phased-in beginning in the 1998 model year and fully implemented in the 2006 model year. A phase-in of the emission standard is necessary to help make the standard technologically achievable. For example, a manufacturer may gradually phase-in new technology across its product line instead of changing all of its product line in a single year. This allows the manufacturer needed flexibility to apply the unproven control technology in a systematic way, given concerns regarding control technology viability and durability. The applicable emission standard for each year of the phase-in is calculated in reference to a baseline curve which describes, on average, the current emission rates of the entire power output range (e.g., 2 horsepower to 300 horsepower) of unregulated OB/PWC engines. EPA's standard structure requires manufacturers to reduce brake specific (i.e., g/kw-hr) HC emissions by at least 75 percent in 2006, the final year of the phase-in.
