The Environmental Protection Agency and the National Highway Traffic Safety Administration submitted its proposed Phase 2 greenhouse-gas emissions and fuel-economy rule for trucks and trailers to the Office of Management and Budget on June 3 for required regulatory review.

That’s the last step before the expansive rulemaking can be finalized. As of now, the two agencies jointly promulgating it project that OMB will complete its review quickly enough that the final rule could be published in the Federal Register as early as August.

A monster of a regulatory development, the proposed Phase 2 rule was unveiled last June. They will cover 2021 to 2027-model-year trucks and tractors and 2018-to-2027 MY trailers.

The big difference with this proposal from the Phase 1 rule is that Phase 2 will regulate trailers for the first time and set GHG limits for complete vehicles– tractor with trailer. The new rule will also set separate engine fuel-efficiency standards for light-, medium-, and heavy-duty vehicles.

The separate engine fuel-efficiency standards would be put into play via discrete steps from the existing 2017 standards to those required for MY 2021, 2024 and 2027 trucks. These proposed standards require a 4% CO2 reduction from 2017 to 2027.

Complying with the engine standards may entail reducing, friction, cutting parasitic loads, using variable valve timing, and making improvements in the exhaust gas recirculation, combustion, and fuel injection systems.

In addition, EPA and NHTSA have projected that up to 10% of heavy-duty engines could have turbo-compounding and 15% of the engines could have waste heat recovery systems by 2027 to meet the strictest standard.

The Phase 2 proposal also addresses natural gas vehicles and engines, including emissions from the crankcase and liquefied natural gas (LNG) boil-off, two of the largest sources of on-vehicle methane emissions.

And the proposed rule affects glider kits. These kits would be subject to GHG limits and would require, starting in 2018, that engines used in them meet the same standards as new vehicles.