Summary of Committee’s First Report: Reducing the Fuel Consumption and Greenhouse Gas Emissions of Medium- and Heavy-Duty Vehicles, Phase Two: First Report
Medium- and heavy-duty trucks, motor coaches, and transit buses—collectively, medium- and heavy-duty vehicles (MHDVs)1—are used in every sector of the economy. The purpose of these vehicles ranges from carrying passengers to moving goods. The fuel consumption and greenhouse gas (GHG) emissions of MHDVs have become a focus of legislative and regulatory action in the past few years. This report is a follow-on to the National Research Council’s (NRC’s) Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles (NRC, 2010; henceforth called the NRC Phase One Report) issued March 31, 2010. That report provided a series of findings and recommendations on the development of regulations for reducing fuel consumption of MHDVs.
On September 15, 2011, the National Highway Traffic Safety Administration (NHTSA) and the U.S. Environmental Protection Agency (EPA) jointly published a Federal Register notice (76 Fed. Reg. 57105) finalizing rules to establish a comprehensive Heavy-Duty National Program to reduce GHG emissions and fuel consumption for on-road MHDVs (the “Phase I rule”).
Subsequently, NHTSA entered into a cooperative agreement with the NRC to issue a report by 2016 on technologies and approaches to reducing the fuel consumption of MHDVs with a view toward beginning work on a revision to the Phase I rule. The committee has since learned that NHTSA and EPA have commenced work on a second round (Phase II) of fuel consumption and GHG emission standards for MHDVs. This first report by the committee provides guidance for the Phase II rule, which is directed at the post-2018 time frame.2 The committee’s final report to be issued in 2016 will cover a broader range of technologies and issues and will address the 2025-2030 time frame.
COMPARISON OF PHASE I RULE WITH THE NRC PHASE ONE REPORT
In 2010, the NRC prepared a report in preparation for the Phase I regulation, proposing several recommendations. On the whole, NHTSA was quite responsive to the Phase I report, in particular on the matter of taking the NRC
1 More precisely, these vehicles include those classified as Class 2b through Class 8, which as a group range in gross (combined) vehicle weight from 8,500 to 80,000 pounds.
2 This Summary contains the key recommendations from the committee’s report.
Phase One Report’s advice on basing the standards on load-specific fuel consumption (LSFC)3 and using modeling to determine compliance. Some recommendations were not adopted by NHTSA, and the committee encourages NHTSA and EPA to do so. In particular, the following aspects remain valid: the importance of data acquisition on the baseline MHDV stock, sales, and performance, without which conclusions on whether the goals of the regulation are met will necessarily be very uncertain; the formation of an expert group to review vehicle simulations, in particular for the Greenhouse Gas Emissions Model (GEM); implementation of driver training programs that may enable reduced fuel consumption; and incremental fuel efficiency gains that could be obtained by dieselization of Class 2b through 7 vehicles. There were other recommendations that NHTSA did not act on, but the above seem to the committee to be the most compelling.
CERTIFICATION USING MODELING AND SIMULATION
From both technical and operational perspectives there is an objective to improve, and even optimize, efficiency metrics for trucks in each class. The existing NHTSA and EPA rules have already addressed the metrics to be employed for engine efficiency, vehicle efficiency, and the associated carbon dioxide (CO2) emissions levels, both for gasoline and diesel. From a practical standpoint at the time of writing, the rules also drive change to provide economic benefit to the truck user. However, as truck efficiency regulation advances, there are trade-offs that must be addressed. Metrics of interest are fuel efficiency, GHGs, cost, criteria pollutants, and energy security. The primary trade-off is GHGs versus fuel efficiency, when several fuels and their associated technologies are considered.
Recommendation S-1: NHTSA, in consultation with EPA, should consider carefully the impact on related metrics when attempting to optimize for a single metric, or should otherwise establish a clearly articulated objective that weights, or places limits on, relevant metrics. (Recommendation 3.1)
GEM is a relatively simple model focused on aerodynamics, rolling resistance, speed, weight, and idle control, and as such it is not capable of acknowledging efficiency and GHG emissions changes associated with engine and transmission design, the integration of advanced powertrains, alternative fuels, hybrid and electric vehicles, and optimal component management. The weight reduction input in GEM is limited to a fixed set of technologies and parts. GEM upgrades are required to provide more realistic prediction of fuel use and GHG emissions, particularly as detailed in the next three recommendations.
Models should be capable of simulating real-world component behavior accurately and should not be over-simplified. GEM specifically does not allow for synergy between components, the operation or control of components in a most efficient way, or the engendering of efficiency through operation of a smaller component at higher relative load. GEM specifies the performance maps for major components such as the engine and transmission and does not credit the vehicle manufacturer with benefits of using a potentially superior engine or transmission.
Recommendation S-2: NHTSA should investigate allowing the original equipment manufacturer (OEM) to substitute OEM-specific models or code for the fixed models in the current GEM, including substituting a power pack (the engine, aftertreatment, and transmission). These models, whether provided by OEMs or fixed in the code, should be configured to reflect real-world operation accurately. (Recommendation 3.7)
Calibration of equipment traceable to national standards for passenger car tires is in place, and self-calibration of equipment is in place for the grading of tires in Europe. Calibration of tire characterization equipment for U.S. regulations should be extended to cover all measurements of coefficients of rolling resistance used in GEM. For tire rolling resistance, there needs to be high confidence in input values to GEM.
3 The precise metric for measuring fuel consumption, the LSFC is measured in gallons of fuel per payload ton per 100 miles. The lower the fuel consumption of the vehicle and the higher the payload the vehicle carries, the lower will be the LSFC.
Recommendation S-3: A mechanism needs to be implemented for obtaining accurate tire rolling resistance factors, including equipment calibration, and maintaining that information in a public database. This might be managed in the same way that tread wear, temperature, and traction data are displayed through the federal Uniform Tire Quality Grading system. (Recommendation 3.4)
GEM employs a limited set of cycles to challenge the simulated truck. These cycles do not include real-world road grade and neglect varying operating weights and aerodynamic yaw angles. Being speed/time based, these cycles also do not allow for the faster acceleration of more powerful trucks, or the longer time that might be taken by less powerful trucks to complete some real-world distance-based routes. This deficiency is not evident in the current model, where a hard-coded engine map, rather than a real OEM engine model, is used.
Recommendation S-4: The choice of test cycles/routes or schedules used in GEM needs to be readdressed thoroughly to avoid creating designs that are optimized for the test rather than achieving real-world performance in the design process. (Recommendation 3.6)
A further issue of importance is the need to collect data on vehicles such as would permit regulators to evaluate the regulatory efficacy and improve both the accuracy of the Phase I rule and any subsequent phases. NHTSA did not include a pilot phase when it promulgated the Phase I rule in 2011. Thus, there were no baseline data from even a few representative national fleets prior to the rulemaking, such as would have enabled comparison with post-rulemaking fuel efficiency. This would have also started to facilitate the comparison of real-world test data with compliance data. The committee nonetheless recognizes that NHTSA has begun the process of designing surveys and seeking the necessary Office of Management and Budget approvals to allow it to assemble a picture of the fleet characteristics, including the collection of R.L. Polk registration data and forecasts, which is appropriate for Class 2b through Class 8 vehicles.
Recommendation S-5: NHTSA should establish a repeatable, reliable collection process as soon as possible. In addition to continuing data procurement with Southwest Research Institute and R.L Polk, NHTSA should investigate outside sources (such as FTR, ACT Research, SmartWay, the North American Council for Freight Efficiency, and the American Transportation Research Institute) to obtain a repeatable, reliable baseline as well as future data. These sources could use the R.L. Polk data and conduct clarifying, deeper interviews with truck and trailer builders, manufacturers, and fleets for specific ongoing data on technologies procured, and fuel consumption. (Recommendation 4.2)
Natural gas accounts for about 25 percent of all U.S. energy use, yet only 0.1 percent is used in transportation, equivalent to about 0.5 billion gallons per year of petroleum fuel. However, in the short time since the release of the NRC Phase One Report (NRC, 2010), natural gas has emerged as an economically attractive option for commercial vehicles. This has been driven by the rapid development of low-cost production of unconventional natural gas.
In order for medium and heavy trucks to use natural gas fuel rather than diesel, the most significant changes from diesel-fueled vehicles are the on-board fuel storage method and the means of introducing and igniting the fuel in the engine. On-vehicle storage is by high pressure, effected by either compressed natural gas cylinders (3,600 pounds per square inch is typical) or cryogenic containers filled with liquefied natural gas. For using natural gas in place of gasoline, the spark-ignition engine carries over with modest changes, but fuel storage is still by one of the above two methods.
Natural gas engines are well developed although improvements can be pursued in engine efficiency, maintenance costs, and on-board vehicle storage costs. Natural gas’s inherent GHG benefit by its low carbon content (approximately 28 percent) is partially negated by lower efficiency in currently available engines and the
higher GHG impact of methane emissions. In addition, a natural gas leakage correction to GHG impact could negate the inherent tailpipe CO2 advantage.
Recommendation S-6: NHTSA and EPA should develop a separate standard for natural gas vehicles as is presently the case for diesel- and gasoline-fueled vehicles. Factors NHTSA and EPA should consider in setting the standard include the maximum feasible ability of natural gas engines to achieve reductions in GHG emissions and fuel consumption, the uncertainties involved with the various alternatives, the impact of duty cycles on the ability to comply with the vehicle standards, the cost of the technology, and rapid growth of the market for natural gas engines and vehicles. This may require additional focused studies. (Recommendation 5.2)
Recommendation S-7: More studies and data are needed to determine the well-to-tank GHG emissions of natural gas vehicles, since current estimates vary significantly regarding quantification of emissions leakage of methane. EPA and NHTSA should assemble a best estimate of well-to-tank GHG emissions to be used as a context for developing future rulemakings. (Recommendation 5.1)
Due to the economics-driven rapid adoption of natural gas, there is urgency to develop an optimum solution in Phase II rule standards for both GHG emissions and fuel consumption (as well as criteria emissions) that will accommodate this fuel without artificially disrupting prevailing commercial transportation business models. As a specific example, the GEM certification tools need to include natural gas engine maps to more accurately quantify the emissions and fuel economy of natural gas vehicles.
Recommendation S-8: To benefit fully from the GHG and petroleum displacement potential of natural gas, government and the private sector should support further technical improvements in engine efficiency and operating costs, reduction of storage costs, and emission controls (as is done for diesel engines). NHTSA and EPA should also evaluate the need for and benefits and costs of an in-use natural gas fuel specification for motor vehicle use. (Recommendation 5.4)
Aerodynamic Devices for Trailers
There are four regions of the tractor-van trailer combination truck that are amenable to aerodynamic design improvements including the various tractor details, the tractor-trailer gap, the trailer underbody, and the trailer tail. Side skirts constitute 90 percent of devices sold to improve aerodynamics. Most side skirts provide a 5 percent fuel saving at 65 mph (3 percent at 55 mph) on EPA testing as part of SmartWay.4 A recent study identified barriers to use of trailers that are more aerodynamically efficient (NACFE, 2013), primarily related to understanding of cost-benefit data and lack of robust application information. Yet, early adopting carriers indicate there is a good return on investment from their use. Nonetheless, manufacturers of trailer side skirts report sales doubled between 2012 and 2013. The manufacturers also report installed prices of side skirts have declined by half.
A California regulation requires operators of van trailers to use aerodynamic devices to reduce the energy required to pull them. Observations made in California and Arizona showed a greater proportion of trailers with aerodynamic devices than did those observations made in Oregon, Texas, Michigan, Pennsylvania, and Maryland. Side skirts were overwhelmingly the predominant aerodynamic device strategy. Other strategies (underbody fairings and rear fairings) were observed just in few instances.
Recommendation S-9: NHTSA, in coordination with EPA, should adopt a regulation requiring that all new, 53 foot and longer dry van and refrigerated van trailers meet performance standards that will reduce their fuel consumption
4 SmartWay is a voluntary program administered by EPA that was formed in 2004 with the objective of improving efficiency and reducing fuel consumption and pollution from movement of freight across the supply chain. Currently it focuses mainly on over-the-road trucking.
and CO2 emissions. The lead time to implement this regulation should be evaluated independently from lead-time requirements applicable to the next set of standards for new engines and tractors, because less time is needed to perform compliance testing and install aerodynamic devices on new trailers. NHTSA and EPA should also collect real-world data on fleet use of aerodynamic trailers to help inform the regulation. (Recommendation 6.1)
The current SmartWay program and California Air Resources Board regulation only address the most commonly used 53+ foot van trailer, which accounts for about 60 percent of the trailers that could potentially benefit from use of aerodynamic devices. Use of aerodynamic devices on other types of trailers, such as container/chassis and shorter vans including dual trailers (“pups”) could provide additional fuel savings of 4 to 9 percent per tractor-trailer, according to industry estimates. Fuel savings from use of side skirts have also been demonstrated on flatbed trailers. The cost effectiveness of using aerodynamic devices on these additional categories of trailers depends on their annual mileage accumulation and average speed, among other considerations such as access to the trailer underbody, and needs further assessment and quantification.
Recommendation S-10: NHTSA, in coordination with EPA, should determine whether it would be practical and cost effective to include with the regulation of van trailers the regulation of other types of trailers such as pups, flatbeds, and container carriers, as doing so could substantially increase overall fuel savings. (Recommendation 6.2)
Various complete truck test procedures, such as the Society of Automotive Engineers (SAE) J1321 and coast-down procedure SAE J1263, used for determining the effectiveness of aerodynamic devices have less precision than necessary to detect small incremental changes. Alternatives such as wind-tunnel testing and computational fluid dynamics simulation should be evaluated because they provide fidelity and better precision. These methods can reduce the cost of development validation, may avoid building of multiple full-size prototypes, and can accelerate development time for the final product. Better test precision and repeatability may induce otherwise skeptical end users to adopt such technologies.
Recommendation S-11: NHTSA should evaluate the relative fidelities of the coast-down procedure and candidate powered procedures to define an optimum prescribed full-vehicle test procedure and process, and should validate the improved procedure against real-world vehicle testing. Furthermore, NHTSA and EPA should assess if adding yaw loads to the validation process provides significantly increased value to the Cd result. In addition, NHTSA and EPA should disseminate to end users updated test data and fuel savings of efficient trailers, aerodynamic devices, and tires, especially to those not participating in the SmartWay program. This should increase end-user confidence in fuel savings and device reliability. (Recommendation 6.3)
Many new tractors and most new trailers are equipped with low-rolling-resistance tires that meet the SmartWay performance standard, and this is likely to increase due to regulatory requirements. However, 70 percent of new tires sold in 2012 for use on tractors and trailers were for replacement of existing tires, and only 42 percent of these are SmartWay verified. There is no assurance in the future that replacement tires will be as energy efficient as the original equipment tires they replace. Manufacturers have also introduced wide-base single tires (WBSTs), many of which feature lower rolling resistance than most dual-tire sets. WBSTs make up less than 10 percent of the commercial truck tire market, but their use is increasing as fleets strive to reduce fuel consumption and GHG emissions.
Recommendation S-12: NHTSA, in coordination with EPA, should further evaluate and quantify the rolling resistance of new tires, especially those sold as replacements. If additional, cost-effective fuel savings can be achieved, NHTSA should adopt a regulation establishing a low-rolling-resistance performance standard for all new tires designed for tractor and trailer use. (Recommendation 6.5)
Precision in tire rolling resistance coefficients (Crr) measurement is mandatory. Furthermore, while the ISO28580 test procedure is given good grades by most in the industry, a robust machine cross-correlation does not exist for commercial vehicle tires in the United States. Carriers cannot depend on the comparability of Crr for measurements from approximately 60 tire suppliers verified by SmartWay.
Recommendation S-13: NHTSA, supported by EPA, should expeditiously establish and validate the equipment and process of a tire industry machine alignment laboratory and mandate the use of that laboratory by each tire manufacturer seeking Crr validation for any tires being offered as candidates in the GEM computation process, just as the Crrs of light-duty vehicle tires were validated. (Recommendation 6.6)
OTHER APPROACHES TO REDUCING FUEL CONSUMPTION
The Phase I rule had the effect of forcing the adoption of technologies for reducing fuel consumption. Such reductions can be achieved by technological improvements to the vehicle as well as by improvements in operations, changes in behavior of drivers, and so forth. The NRC Phase One Report considered other approaches (referred to, perhaps imprecisely, as nontechnical approaches), such as intelligent transportation systems, construction of lanes exclusively for trucks, congestion pricing, driver training, and intermodal operations (NRC, 2010, pp. 159 et seq.). Also considered were market-based instruments such as fuel taxes. Another viable approach would entail adjusting size and weight restrictions on trucks. For example, this might include greater use of vehicles that have favorable LSFC such as longer combination vehicles, which have greater freight capacity than the notional tractor-trailer, which can have a combined gross vehicle weight of 80,000 pounds.5 While some nonvehicle alternative approaches for reducing fuel consumption and greenhouse gas emissions may be beyond NHTSA’s delegated authority, the Agency can work with other agencies with appropriate authority as well as encourage private actors to consider such strategies to complement and support NHTSA’s standards.
Recommendation S-14: NHTSA should consider additional strategies to encourage the adoption of measures that reduce fuel consumption and attempt to quantify the impacts of nontechnological factors on the costs and feasibility of future efforts to improve fuel consumption. (Recommendations 1.9 and 1.11)
The committee also has made several observations about the regulatory process. Currently NHTSA and EPA standards consider fuel efficiency of the vehicle (in gallons per ton-mile) and tailpipe CO2 emissions (in grams of CO2 per ton-mile) that need to be achieved, on average, by the mix of vehicles sold each year by each manufacturer. Manufacturers are likely to achieve these vehicle standards using a variety of different energy fuels and technologies. Failure to consider the well-to-wheel emissions of each combination of fuel and vehicle technology may lead to regulations that do not achieve the anticipated energy and GHG emissions savings. Furthermore, there is the possibility that regulations could produce incentives and behaviors that may result in unintended consequences that could be beneficial or detrimental, such as the water contamination that resulted from the addition of methyl tertiary-butyl ether to gasoline as an oxygenate intended to reduce ground-level ozone.
Recommendation S-15: NHTSA, in coordination with EPA, should begin to consider the well-to-wheel life-cycle energy consumption and greenhouse gas emissions associated with different vehicle and energy technologies to ensure future rulemakings best accomplish their overall goals. (Recommendation 1.10)
Recommendation S-16: NHTSA should conduct an analysis, including methods such as expert surveys and scenario analysis or red teaming, as appropriate, to anticipate and analyze potential unintended consequences of its
5 This follows from the observation that “weighing out” gives advantage for fuel consumption versus “cubing out”—the latter referring to filling up the cargo area before reaching the combined gross vehicle weight limit.
regulations and to determine whether additional actions are warranted to try to minimize such impacts. NHTSA should undertake this analysis concurrently with its next revision to its regulation. (Recommendation 1.4)
Regarding the potential for technological change in the model year 2019-2022 time frame, the committee, in its investigations to date, has not identified any combustion or other engine technologies beyond those identified in the NRC Phase One Report (2010) that would provide significant further fuel consumption reduction during the Phase II rule time frame. However, those technologies identified in the NRC Phase One Report should be updated with current projections for fuel consumption reduction and adjusted for system interactions when used in combination with each other.
A further issue relates to timing and rate at which technology enters the marketplace. In establishing the stringency of a Phase II rule, careful evaluation of technology penetrations is necessary. While the NHTSA-stated intent of the Phase I rule was to base targets on off-the-shelf technologies, the new baseline for setting a Phase II rule will be drawn from more current vehicles and will consider the different degrees of penetration attained by both off-the-shelf and future and advanced technologies by 2018.
Recommendation S-17: NHTSA’s Phase II rule should take the current and projected incremental fuel consumption reductions and penetration rates of the various technologies into careful consideration: These incremental reductions and penetration rates should be updated from those that were projected in the Phase I rulemaking. Furthermore, system interactions should be evaluated for the effect on the projected incremental reductions whenever combinations of technologies are considered. (Recommendation 2.2)
NACFE (North American Council for Freight Efficiency) and Cascade Sierra Solutions. 2013. Barriers to the Increased Adoption of Fuel Efficiency Technologies in the North American On-Road Freight Sector. July.
NRC (National Research Council). 2010. Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles. Washington, DC: The National Academies Press.