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The use of devices to reduce aerodynamic drag on large trailers and save fuel in long-haul, over-the-road freight operations has spurred innovation and prompted some trucking fleets to use them in combinations to achieve even greater gains in fuel-efficiency. This paper examines aerodynamic performance and potential drag reduction benefits of using trailer aerodynamic components in combinations based upon wind tunnel test data. Representations of SmartWay-verified trailer aerodynamic components were tested on a one-eighth scale model of a class 8 sleeper tractor and a fifty three foot, van trailer model. The open-jet wind tunnel employed a rolling floor to reduce floor boundary layer interference. The drag impacts of aerodynamic packages are evaluated for both van and refrigerated trailers. Additionally, the interactions between individual aerodynamic devices is investigated.

During the 1980s, the U.S. Environmental Protection Agency (EPA) incorporated the R factor into fuel economy calculations in order to address concerns about the impacts of test fuel property variations on corporate average fuel economy (CAFE) compliance, which is determined using the Federal Test Procedure (FTP) and Highway Fuel Economy Test (HFET) cycles. The R factor is defined as the ratio of the percent change in fuel economy to the percent change in volumetric heating value for tests conducted using two differing fuels. At the time the R-factor was devised, tests using representative vehicles initially indicated that an appropriate value for the R factor was 0.6. Reassessing the R factor has recently come under renewed interest after EPA's March 2013 proposal to adjust the properties of certification gasoline to contain significant amounts of ethanol.

As part of the EPA's ongoing in-use vehicle emissions compliance program, two hybrid vehicles were tested. A 2001 Honda Insight and a 2001 Toyota Prius were tested on a chassis dynamometer at the National Vehicle Fuel and Emissions Laboratory. Both vehicles were run on the Federal Test Procedure drive cycle. Emissions were measured simultaneously using the SEMTECH-G Portable Emissions Measurement System (PEMS) for comparison to the chassis dynamometer bench analyzer. The correlation for cumulative emissions (bag) between dynamometer and on-board analyzer were adequate for CO2, CO, and NOx, though the PEMS HC measurements were low by comparison. The measurements were limited by the very low exhaust volume flow rates on both vehicles. A more sensitive flow meter will be required to measure emissions from vehicles certified to SULEV standards.