Revisions to In-Use Testing for Heavy-Duty Diesel Engines and Vehicles; Emissions Measurement and Instrumentation; Not-to-Exceed Emission Standards; and Technical Amendments for Off-Highway Engines

EPA is taking direct final action on several revisions to EPA's mobile source emission programs standards and test procedures. EPA believes that each of these is minor and non-controversial in nature. Most of the changes arise from the results of the collaborative test program and related technical work we conducted for the highway heavy-duty diesel in-use testing program. Most noteworthy here is the adoption of a particulate matter measurement allowance for use with portable emission measurement systems. Related to this are two provisions to align the in-use program timing requirements with completion of the program as required in current regulations and the incorporation of revisions to a few technical requirements in the testing regulations based on information learned in this and one other test program. Finally, the DFR modifies a few transitional flexibilities for locomotive, recreational marine, and Tier 4 nonroad engines and incorporates a handful of minor corrections.