Review of the 21st Century Truck Partnership (2008)

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5 Parasitic Losses of Energy INtroduction • Goal 4: —A. Increase heat-load rejected by thermal manage- The role of parasitic losses of energy has been important ment systems by 20 percent without increasing radiator throughout the history of the 21st Century Truck Partnership size to accommodate future increased engine power (21CTP). The latest statement of overall goals for reduc- requirements or allow reduced radiator and cooling tion of parasitic energy loss is in the Partnership’s updated system size at constant power. roadmap (DOE, 2006a). The goals in this area have been —B. Develop and demonstrate technologies that refined substantially since the version of the year 2000 reduce powertrain and driveline losses by 50 percent, (DOE, 2000). thereby improving class 8 fuel efficiencies by 6 to The energy audit data for the parasitic loss elements for 8 percent. the baseline and the target goals is given in Table 5-1, listed • Goal 5: by goal. —Reduce tire rolling resistance values relative to existing best-in-class standards by 10 percent without Goals and Objectives compromising cost or performance. (This has not been an active area of research.) The technical goals and milestones for parasitic losses The five goals are discussed in the text that follows. given in the latest versions of the 21CTP Roadmap (DOE, 2006a): Goal 1: Develop and Demonstrate Advanced • Goal 1: Technology Concepts That Reduce the —Develop and demonstrate advanced technology Aerodynamic Drag Of A Class 8 concepts that reduce the aerodynamic drag of a class Tractor-Trailer Combination by 20 percent 8 highway tractor-trailer combination by 20 percent (from a Current Average Drag Coefficient of (from a current average drag coefficient of 0.625 to 0.625 to 0.5) 0.500). • Goal 2: Background —Develop and demonstrate technologies that reduce The 21CTP’s efforts in the area of aerodynamic drag essential auxiliary loads by 50 percent (from current reduction followed directly from activities undertaken under 20 hp to 10 hp) for class 8 tractor-trailers. the DOE Heavy Vehicle Aerodynamics Multiyear Program • Goal 3: Plan (MYPP) (DOE, FCVT, 2006a), which had its beginning —(21CTP-003)—Develop and demonstrate light- at the First DOE Workshop on Heavy Vehicle Aero­dynamic weight material and manufacturing processes that Drag, held in Phoenix, Ariz., on January 30-31, 1997 lead to a 15 to 20 percent reduction in tare weight (McCallen et al., 1998). The goal of the group as stated in (for example, a 5,000-lb weight reduction for class 8 the MYPP was as follows (DOE, 2006b): t ­ractor-trailer combinations). The goal of the proposed activities is to develop and demon- strate the ability to simulate and analyze aerodynamic flow 70 

PARASITIC LOSSES OF ENERGY 71 TABLE 5-1  Energy Audit—Baselines and Targets (80,000-lb Gross, 65-mph Level Road) Improvement Goal/Technical Area Baseline Target Delta (percent) Primary Technology Goals Goal 1: Aerodynamic losses 85 kW/114 hp 68 kW/91 hp 17 kW/23 hp 20 Goal 2: Auxiliary loads 15 kW/20 hp 7.5 kW/10 hp 7.5 kW/10 hp 50 Goal 3: Reduce tare weight 12,245 kg/ 9,795 to 10,410 kg/ 1,837 to 2,450 kg/ 15 to 20 27,000 lb 21,600 to 22,950 lb 4,050 to 5,400 lb Other Technology Goals Goal 4: Thermal management and friction and wear   Goal 4a: Waste heat rejection Increase in cooling heat rejection by 20 percent without increasing radiator size.   Goal 4b: Powertrain losses 9 kW/12 hp 4.5 kW/6 hp 4.5 kW/6 hp 50 Goal 5: Rolling resistance 10 percent reduction relative to existing best in class SOURCES: DOE, 2000; DOE, FCVT, 2006. around heavy truck vehicles using existing and advanced The reports for 2005 reaffirm this statement of goals. computational fluid dynamics (CFD) tools. The final prod- Reports on the work on aerodynamic drag from 2006 appear ucts are validated CFD tools that can be used to reduce in a different form as parts of the annual progress report of aerodynamic drag of heavy truck vehicles and thus improve the Heavy Vehicle Systems Optimization Program (DOE, their fuel efficiency. FCVT, 2005a) and the 2000 Heavy Vehicle System Review (NRC, 2000a). The team included participants from DOE national The work began, as the goal statement reflects, with a laboratories, universities, and the National Aeronautics and primary focus on computational tools and with experiments Space Administration (NASA). Visits were made to truck expected to serve the purpose of supporting the compu- and trailer manufacturers to get their views on the issues tational tool developed, as opposed to the experimental to overcome in order that lower drag heavy vehicles would program being a parallel path for development of drag reduc- be commercially viable. Workshops were held and reports ing design features. The computational tools on which the on the work of the various participants were issued on a majority of resources were expended were codes that had regular basis through 2005. These reports are available at their origins at the national laboratories. By 2001 a number the DOE Scientific and Technical Information web site. In of truck manufacturers were invited to the working group each working group report the project goals were reaffirmed meetings and made presentations on their approaches to in the following form through 2003 (with some variation in aerodynamic development. The principal manufacturers all the items listed in parentheses in the last line): had small in-house teams who had a history of doing experi- mental development in wind tunnels and who had recently • Perform heavy vehicle computations to provide guid- begun evaluating and using commercial computational fluid ance to industry dynamic (CFD) codes. Although the truck manufacturers • Using experimental data, validate computations were somewhat interested in the claims of the team about the • Provide industry with design guidance and insight into potential power of their CFD codes, their opinion was that the flow phenomena from experiments and computations only way the features would become feasible for industry use • Investigate aero devices (e.g., boattail plates, side would be if the features were incorporated into commercial extenders, . . .) codes that would be accessible to all and maintained for customers over time. In the report of the July 2004 meeting of the working The DOE heavy vehicles team organized a conference group (the last line was changed as follows including the on the aerodynamics of heavy vehicles (DOE, 2004). Kevin bold type for the last part of the statement). Cooper of the National Research Council, Canada, gave the keynote paper, “Commercial Vehicle Aerodynamic Drag • Investigate aero devices with emphasis on collabora- Reduction: Historical Perspective as a Guide” (Cooper, tive efforts with fleet owners and operators. 2004). Cooper gave a concise history of prior work on truck aerodynamics and demonstrated that data were already avail- able to allow assessment of the potential of a number of drag reducing devices including tractor-trailer gap closure, trailer Available at http://www.osti.gov/. skirting, and boat-tailing, and had been available for several 

72 REVIEW OF THE 21ST CENTURY TRUCK PARTNERSHIP decades. He cited a number of important sources that do Around 2004, a project was initiated under a contract with not appear in any references in the reports on the DOE HV the Truck Manufacturers Association, with the title “Test, program. Cooper challenged the following claims, which Evaluation, and Demonstration of Practical Devices/Systems appeared in the then-current version of the MYPP ­(McCallen to Reduce Aerodynamic Drag of Tractor/Semi-trailer Combi- et al., 1998). nation Unit Trucks.” The participants were Freightliner LLC, International Truck and Engine Corp., Mack Trucks, Inc., At present the aerodynamic design of heavy trucks is based and Volvo Trucks NA. Reports on this project appear in the largely upon wind tunnel estimation of forces and moments, 2005 and 2006 annual progress reports on the Heavy Vehicle and upon qualitative streamline visualization of flow fields. Systems Optimization Program (DOE, FCVT, 2005a, 2006). No better methods have been available traditionally, and the Each of the companies focused on a different aspect of the designer/aerodynamicists are to be commended for achiev- tractor-trailer aerodynamics. The combined results in 2006 ing significant design improvements over the past several indicate a potential for meeting the 20 percent reduction decades on the basis of limited quantitative information. in drag that has been the target since the first technology The trucking industry has not yet tapped into advanced design roadmap. approaches using state-of-the-art computational simulations to predict optimum aerodynamic vehicles. Computational Goals, Targets, and Timetables analysis tools can reduce the number of prototype tests, cut manufacturing costs, and reduce overall time to market. The goal for aerodynamic drag reduction has been a 20 percent reduction of drag coefficient from 0.625 to 0.5 since Cooper went on to report on a case study undertaken the first technology roadmap (DOE, 2000). Although mention over a three-week period (which again validated the size has been made from time to time of achieving the target by and plausibility of the existing program goals) leading up to a particular date, the working documents have not included his presentation in which the Canadian National Research timetables as part of the primary goals and objectives. Council took an existing truck model, fabricated tractor and In fact, the frequently restated goals of the program front trailer skirts, fabricated beveled base panels to emulate appearing in every report of a workshop meeting as quoted a simple boat tail, fabricated skirts for the area behind the in the background section do not mention the technology trailer wheels, fabricated a gap seal between tractor and roadmap goal for drag coefficient or a timeline, but instead trailer, and fabricated a filler block to completely close and are stated in terms of process. DOE should make sure that fill the gap. Design had to be done before the fabrication. In truck manufacturers have commercial CFD codes that are one 8-hour shift of wind tunnel time the effect of these parts usable for making aerodynamic drag calculations. singly and in selected combinations on drag was measured over yaw angles from –20 to +20 degrees. The results get Progress Toward Objectives close to the Technology Roadmap target of a drag coefficient of 0.5, even though the tractor itself is not as streamlined as As reported by McCallen, devices have been identified a number of currently available tractors. that will reduce drag to the target levels. A reading of the Another project carried out under the Heavy Vehicle reports and related information as cited in the background Aerodynamic Drag Program is quite distinct and has been section indicates that methods and devices capable of achiev- an active project for almost the entire period from the initial ing the target levels were already available as the MYPP was MYPP. The project explored the potential for pneumatic being put together. Practical problems of implementation devices to actively control flow separation in critical regions were and remain major barriers to application of known to reduce drag. This project has provided some substantial techniques. Since the barriers to implementing modified drag reductions. However, the methodology remains ques- aerodynamic designs are potentially different for each fleet tionable for practical use because of the complexity of the owner or operator, CFD design tools may prove to be helpful active devices. The project team from the Georgia Tech to truck and trailer manufacturers in exploring the multitude Research Institute continues to develop the systems. of design changes to address the needs of individual fleet As mentioned earlier, input from truck manufacturers owners. It appears that these CFD programs have been devel- beginning about 2001 indicated that commercial CFD codes oped to handle aerodynamic design issues, because they are were more likely to become useful tools for industry than currently used by race car builders. the codes developed in the national laboratories due to ease of use issues and code maintenance. A project was added to Rose McCallen et al., “DOE’s Effort to Reduce Truck Aerodynamic the program led by Argonne National Laboratory to evalu- Drag through Joint Experiments and Computations.” Presentation on work ate commercial codes by applying selected ones to the same performed under the auspices of the U.S. Department of Energy by the geometries that were the subject of simulation in the ongoing University of California, Lawrence Livermore National Laboratory ­under projects using national laboratory codes. Contract W-7405-ENG-48. April, 2006. Available at http://www1.eere. energy.gov/vehiclesandfuels/pdfs/hvso_2006/02_mccallen.pdf. ­ Accessed June 2, 2008. 

PARASITIC LOSSES OF ENERGY 73 Goal 2. Develop and Demonstrate • Modular HVAC Unit Technologies That Reduce Essential • Shore Power Electrical Converter Auxiliary Loads By 50 percent (From Current • Integrated Starter-Generator 20 Hp To 10 Hp) For Class 8 Tractor-Trailers • Electric Oil Pump • Electric Compressed Air Module Background • Electric Water Pump In all modern vehicles powered by internal combustion In addition, the necessary power distribution architecture engines, there are auxiliary components and subsystems was developed, integrated and tested, as were the supervisory that are necessary to operate the vehicle. Examples of these control algorithms. The removal of these auxiliaries from the a ­ uxiliaries are the alternator, power steering pump, air engine system loads also reduces the radiator heat loading, conditioning compressor, and pneumatic air compressor. since less fuel is consumed by the main engine for the same Additional power requirements which consume energy that propulsion energy. otherwise would propel the vehicle and are closely associ- Caterpillar reported a demonstrated fuel economy ated with the powertrain but nonetheless reduce the overall improvement of 1 to 2 percent in over-the-road operation. efficiency of the vehicle include the oil pump, coolant pump, Assuming an average operational power of 250 hp, this repre- fuel injection pump, fuel supply pump, transmission, and dif- sents a reduction in auxiliary loading of about 2.5 to 5 hp. ferential gear sets. This group of components and subsystems The anti-idling of the main engine was offset by the use are addressed in the chapter under Goal 4: Thermal Manage- of a small diesel powered auxiliary power unit (APU) and a ment and Friction and Wear. shore-power converter for use in an electricity-enabled over- night parking center. This strategy demonstrated the potential Engine Accessories to provide an additional 5 to 7 percent yearly fuel savings. A more detailed discussion concerning idle-­reduction tech- The parasitic losses associated with auxiliary loads nologies and programs conducted under the 21CTP program are approximately 20 hp for a typical heavy-duty vehicle are included in Chapter 6 of this report. (DOE, FCVT, 2006). To minimize additional power transfer losses, these components are normally directly driven by the engine crankshaft or camshaft through a series of the Other Parasitic Loss Reduction Program serpentine belts, chains or gear sets. The decision to drive During the period FY 2005-FY 2007, many other pro- these ­auxiliaries off the crankshaft or camshaft is influenced grams were classified under the general heading of “Reduc- by in-vehicle packaging constraints, rotational speed ranges ing Essential Power Loads by 50 Percent.” Although some of the individual components and other system dynamic fac- of these may tend to cross over into other technical areas tors such as torsional excitation, system natural frequencies, of focus, such as secondary energy recovery through turbo- and under-hood heat sources. compounding, they all are associated with increasing the Besides the actual design and internal mechanical losses percentage of fuel energy that is used to propel the vehicle. of the auxiliaries themselves, a condition that directly A partial list of these programs includes: impacts their efficiency of operation is their direct connec- tion to the engine. This results in many non-optional com- • Advanced Brake Systems for Improved Undercarriage promises that reduce operational efficiency over the engine Aerodynamic Flow and vehicle duty cycle. One example of this compromise is —Evaluated impact of new brake materials and the power steering pump; where sufficient pressure to navi- designs on undercarriage aerodynamic flow gate the vehicle under low speed conditions results in excess —Assessed effect of design and material improve- pressure at high vehicle speeds, where limited power steering ments on necessary brake cooling, under-hood tem- assistance is needed. perature and overall vehicle thermal management Under the 21CTP program, several projects directed • Evaluate Autothermal Diesel Reformer toward the optimization of operational parameters for —Assessed fuel injection technology that could allow a ­ uxiliaries have been conducted. The most noteworthy of autothermal diesel reformation that would produce these has been the More Electric Truck (MET) program hydrogen to be used by on-board fuel cell APU conducted by Caterpillar. • Optimize Boundary Layer Lubrication Mechanisms The MET program focused on the design, development, for improved friction characteristics and component and demonstration testing of electrically powered auxiliary life components and systems that would allow anti-idling opera- —Developed a model for scuffing mechanism based tion (main engine shut-off, yet offering auxiliary power for upon adiabatic shear instability accessories and/or cabin heating/cooling). The subsystems —Established and validated performance and failure included: prediction methodologies for lubrication systems 

74 REVIEW OF THE 21ST CENTURY TRUCK PARTNERSHIP —Applied X-ray-based techniques to characterize • Develop Integrated Under-hood Thermal Analysis tribofilms for Cooling System Optimization and Radiator Size —Eaton Corporation demonstrated methods to improve Reduction drivetrain efficiency achieving a 2.5 percent improve- —Developed predictive capability in cooperation with ment in vehicle fuel efficiency Cummins to identify hot-spots inside divided engine • Reduce Engine Friction by Advanced Tribological compartments of off-road machine Concepts —Prototypical test rig constructed at Caterpillar and —Evaluated potential friction reduction through the experiments conducted to validate 1D and 3D simula- use of advanced lubricants, additives, and low-friction tion methods engineered surfaces —Validated integrated system analysis methodology —Developed engine/vehicle models to predict fuel for effects of ventilation on heat rejection and compo- economy savings nent temperatures —Predicted fuel economy improvement of 0.5– • Powertrain System Efficiency Improvement through 1.4 percent with low friction surfaces Reduction of Friction and Wear • Improved Cooling Fan and System Performance and —Cooperative program conducted with Eaton Corpo- Efficiency ration to reduce friction and parasitic energy losses in —Designed and demonstrated 5 percent flow and truck transmissions and axles 10 percent efficiency improvement of large axial fan —Conducted friction predictions utilizing a range of —Demonstrated improvements of aerodynamic fan surface characteristics, lubricants and surface topogra- shroud phies of gears —Demonstrated high pressure air fine debris filtration —Demonstrated significant potential for parasitic for high performance radiators energy loss reduction • Determine Feasibility of Nanofluid Application —Calibrated rough surface contact model using test in Heavy Vehicle Engine Cooling for Improved data Efficiency —Developed and calibrated in-situ boundary film —Designed, fabricated and tested experimental test analysis capability facility —Quantified experimental test section heat losses Finding 5-1. The More Electric Truck program demon- • Evaluate boiling critical heat fluxes and pressure strated an integrated system to reduce idling emissions and drops of nanofluids Efficient Cooling in Engines with fuel consumption. The test program showed significant N ­ ucleate Boiling progress toward achieving the objectives of Goal 2 in Chap- —Reduced cooling system size by development of ter 5 (“Develop and demonstrate technologies that reduce more efficient heat transfer method essential auxiliary loads by 50 percent, from the current —Developed two-phase flow engine cooling heat 20 hp to 10 hp, for Class 8 tractor-trailers”) and Goal 6 in transfer rates and pressure drops Chapter 6 (“Produce by 2012 a truck with a fully integrated —Determined practical limits of engine coolant idling-reduction system to reduce component duplication, boiling weight, and cost”). It did so by demonstrating 1 to 2 percent • Develop Nanofluids with Ultra-high Thermal estimated reduction in fuel use including significant truck Conductivity idling reductions. According to DOE, this translates into an —Developed gold-based nanoparticle-water suspen- overall annual fuel savings for the U.S. fleet of 710 million sion that increased thermal conductivity by 10 percent to 824 million gallons of diesel fuel (about $2 billion per over water year at $2.75 per gallon). —Conducted laminar flow experiments and developed analytical model for effective viscosity of nanofluids Recommendation 5-1. Given the potential of this program • Determine Erosive Effects of Nanofluids for High to save fuel, the committee recommends that the 21CTP Efficiency Radiator Systems continue the R&D of the identified system components that —Analyzed and developed predictive models for will provide additional improvements in idle reduction and erosion of radiator systems caused by the use of parasitic losses related to engine components that are more nanofluids efficient and provide better control of energy use.  The —Measured baseline data on erosion of aluminum program should focus also on the cost-effectiveness of the radiator systems due to use of Cu-based nanofluid technologies. —Evaluated tribological effects of nanofluids Finding and Recommendation 5-1 are identical to Finding and Recom- mendation 6-7 (in Chapter 6, “Engine Idle Reduction”). 

PARASITIC LOSSES OF ENERGY 75 Goal 3: Develop and Demonstrate specific vehicle components and systems, resulting in hard- Lightweight Material And Manufacturing ware demonstration projects. Materials under consideration Processes that Lead to a 15 percent to included aluminum, high strength and stainless steels, and 20 percent Reduction In Tare Weight (For composite materials including carbon reinforced composites. Example, A 5,000-Lb Weight Reduction For The total lightweight materials budget averaged from $8 mil- Class 8 Tractor-Trailer Combinations) lion to $9 million from 2000 through 2005, and was reduced to $2.7 million in 2006. As a result of the reduction of the Background total 21CTP budget in FY 2007, the lightweight materials program was discontinued. Nevertheless the committee has An important objective of the program was to explore reviewed the program to date. vehicle weight reduction opportunities through the appli- cations of lightweight materials, including high strength steels, aluminum, and advanced composites. Previous Progress Toward Objectives demonstration programs have shown the potential to reduce Numerous separate projects were initiated to support the weight of light vehicles by over 20 percent using high the program, spanning the application of steel, aluminum, strength steels, and by as much as 50 percent using carbon titanium, magnesium, and glass and carbon reinforced reinforced composites (NRC, 2000b), and similar opportuni- composites. A number of different partners from industry, ties were cited for application to U. S. Army trucks (NRC, notably involving major truck manufacturers, participated 2003). The primary barriers to weight reduction in vehicles in the program. Several of the projects (taken from 21CTP are the costs not only of the raw material but also of the Project Quad Sheets (DOE, 2007) and the 2005 merit review manufacturing technology required for production. Most (DOE, FCVT, 2005b) are listed below: vehicles today, including heavy trucks, utilize mild steel for body ­ applications—the fabrication, assembly, and joining • Carbon fiber composite hoods and fairings for class 8 technologies for mild steel are well developed and optimized trucks for low cost. Nevertheless, the transition to high strength • Ultralight (stainless steel) transit bus steels from mild steel is relatively straightforward and has • SPF (super plastic forming) aluminum vehicle body been progressing well in the automobile industry because, panels while there is a modest premium for the higher-strength • Cast magnesium metal matrix composites for compo- steels, existing fabrication and body assembly processes need nents (e.g. transmission case) little modification. Aluminum presents more of a ­challenge • Friction stir joining (FSJ) in application to using tailor because of its inherently higher raw material cost, and also welded blanks for aluminum panels because of differences (from steel) in fabrication and joining. • Titanium processing development for application to Carbon reinforced composites, while offering the greatest truck leaf springs weight reduction potential, require special methods for fabri- • Investigation of non-homogeneous microstructures cation and assembly, and are only now being used by a com- due to heat treatment of steel mercial aircraft manufacturer for extensive application in the • Equal channel angle extrusion processes development fuselage and wing structures. In addition, carbon fiber costs for aluminum alloy metal matrix composites are very high (several dollars per pound compared with mild • Lightweight diesel engine components (cylinder and steel at well under a dollar a pound), and carbon fiber costs liner) may remain high as demand grows in the aircraft industry. • Development of graphite foams for lightweight heat exchangers Goals, Targets, and Timetables • Advanced materials for friction brakes • Lightweight trailer project The overall goal for the program was to develop and dem- • Basic studies of ultrasonic welding onstrate, by 2012, lightweight material and manufacturing processes that would enable a reduction in vehicle weight While this is not the complete list of lightweight projects, of from 10 percent to 33 percent depending on vehicle type it serves the committee’s purpose of discussing the strategy (DOE, 2006a). For Class 8 trucks, the goal was a weight employed in the lightweight materials program. Evaluating reduction of from 15 percent to 20 percent in tare weight, a number of different materials is a good approach to use which is equivalent to a 5,000 lb weight reduction for a Class 8 early in this type of program, as it enables identification of tractor-trailer combination. Cost targets associated with the “best applications,” in order to “down-select” the best mate- weight reduction targets were not cited in DOE (2006a). The rial for a specific application. And indeed, certain materials approach included the application of lightweight materials to are likely to be the most promising for specific components and subsystems. In addition it is important to fund support- See www.boeing.com/commercial/787family/background.html. ing projects such as joining and materials processing for 

76 REVIEW OF THE 21ST CENTURY TRUCK PARTNERSHIP advanced materials. On the other hand, funding so many decision for several reasons. First of all, improvements to the disparate projects seriously constrains the budget allotted engine have greater potential for reducing fuel consumption to each individual project, and therefore the progress of the than do technologies associated with vehicle weight reduc- weight reduction program. tion. In addition, many of the materials under consideration Nevertheless, good progress was made on the individual have been used in commercial automotive application; there- projects, and in many cases the results demonstrated the fore, the opportunity for new discovery through research potential for achieving significant weight reduction in vari- seems less likely than is the case for engine and emis- ous components and subsystems. However, it was not pos- sions technology. Finally, as previously mentioned, further sible to determine whether or not the program would likely development and production implementation of the vehicle meet the objective of 15 percent to 20 percent weight savings materials technology should be the responsibility of the because a full system analysis of a truck incorporating the manufacturers rather than that of the federal government. various lightweight components was not presented. In addi- tion, the issues of material costs and costs of developing new Finding 5-2. The 21CTP lightweight materials research was fabrication, joining, and assembly systems for production terminated as a result of the 2007 budget reduction. remain to be resolved. Of course, it is appropriate that the truck manufacturers, rather than the federal government, be Recommendation 5-2. The committee agrees with the deci- responsible for both full system integration and production sion to terminate lightweight materials research in order to implementation; nevertheless it would have been instructive provide as much budget resource as possible to continue to have had a preliminary analysis of the net weight reduc- research in engine efficiency and emissions reduction tech- tion of a heavy truck due to the integrated application of nologies, as improvements in engine efficiency offer greater the individual component projects (as was attempted for the potential for overall gains in vehicle fuel efficiency. steel bus project). Due to the aforementioned reduction in the 21CTP bud- Finding 5-3. Prior to termination of the lightweight materials get, the lightweight materials program has been terminated. program, several lightweight material projects demonstrated Yet it might be instructive to consider logical next steps. Prior weight reduction potential for truck components. However, to production, an original equipment manufacturer (OEM) the program did not achieve the longer term objective would develop prototype vehicles with the new materials (planned for 2012) of demonstrating a 5,000-pound weight technology fully integrated into the vehicle. The prototype reduction for a complete class 8 tractor trailer combination. vehicles would undergo stringent validation schedules to ensure durability, corrosion resistance, resistance to ultra- Recommendation 5-3. Due to the termination of the project violet exposure for painted surfaces, reliability, and main- in 2007, it will be the responsibility of truck manufacturers to tainability. At the same time, the OEM would begin a cost take the next steps of system integration, product validation, analysis to predict the finished cost of a production vehicle. and ultimately production of a lightweight truck. Although The cost analysis would include the investment required to an interim step of system integration at the pre-production establish, if necessary, a new body shop (where the body pan- stage would have been useful, it is not inappropriate that the els are fabricated and joined), a new paint shop (new painting OEMs now assume responsibility for continuation of the process for lightweight materials), and a new assembly line. work, as the next steps will require development of a busi- Production technologies and systems are considered to be ness case which comprehends material costs and the costs of important competitive assets, and therefore manufacturing modifying existing manufacturing systems to accommodate technologies are sometimes treated as company confidential. the introduction of advanced materials. For this reason, it would be expected that the truck manufac- turers would pursue scale up and production individually. GOAL 4A: THERMAL MANAGEMENT AND FRICTION In summary, the initial strategy and goals of the light- AND WEAR—INCREASE HEAT-LOAD REJECTED BY weight program were sound. Many of the individual ­projects THERMAL MANAGEMENT SYSTEMS BY 20 PERCENT made good technical progress resulting in a number of WITHOUT INCREASING RADIATOR SIZE options for truck manufacturers to consider for further development and deployment. Indeed, a few projects were The background and approach for Goal 4A are described carried to production (e.g., composite truck bed for pickups). in the 21st CTP Roadmap and Technical White Papers (DOE, Clearly as these technologies mature and as they move into 2006a) and are discussed and summarized below. production, the responsibility should shift from the 21CTP The focus of this goal is to reduce truck radiator size to the individual original equipment manufacturers. through efficient cooling systems, advanced nanofluid cool- Due to the 2007 budget reduction, DOE management elected to terminate the lightweight materials project in order Ken Howden, DOE, FCVT, “Partnership History, Vision, Mission, and to maintain as much resource as possible focused on engine Organization,” Presentation to the committee, Washington, D.C., Febru- and emissions technology. The committee agrees with that ary 8, 2007, Slide 21. 

PARASITIC LOSSES OF ENERGY 77 ants and improved under-hood design through the use of budget for the 21st CTP could fund. The committee assumed advanced modeling techniques. Exhaust gas recirculation that this was the case since no projects or results from any of (EGR) is the most common near-term strategy for reducing the above research areas were provided. NOx emissions, but is expected to add 20 to 50 percent to the coolant heat-rejection requirements. Thus, there is a need Recommendation 5-4. In addition to identifying a list of to package more cooling capability into a smaller package research areas that could provide solutions to thermal man- space without increasing cost. Benefits in fuel efficiency are agement challenges, DOE should develop, fund, and imple- projected to be achieved through the development of high- ment plans for pursuing the key areas that will lead to the performance heat exchangers and cooling media (fluids) successful accomplishment of the specific 21CTP Goal 4A. which will reduce the need for high-output engine water DOE’s first step should be to assess the candidate technology pumps. or technologies that have the highest potential for meeting Longer term, the trend toward hybrid vehicles is expected the requirements of Goal 4A. to further increase the demand on coolant heat rejection systems. In diesel hybrid vehicles, there are up to five This goal and its status were briefly discussed with the separate cooling systems (for the engine, batteries, motors, committee and the following information was provided: e ­ lectronics, and charge air). “Track and laboratory tests met or exceeded goals, validation These demands for improved thermal management sys- test is underway.” Unfortunately, a description of the track tems have created a need for new and innovative thermal and laboratory tests that had been performed, the engineering management technologies that will require long-term R&D. details and the results from these tests, or a description and Several research areas were identified by DOE and industry timetable for the validation test reported to be under way that could provide both near-term and long-term solutions were not described for the committee. to these thermal management challenges. The research areas identified were as follows: Finding 5-5. Based on the above observations, the commit- tee was not able to accurately assess the progress on this goal • Intelligent thermal management systems or the expectation of whether this goal can be successfully —Use of higher electrical bus voltage to enable the use achieved. of variable speed electric pumps and fans —Variable shrouding Recommendation 5-5. DOE should provide periodic status —Integration of thermal management components into reports on the 21CTP goals that include the technical status the vehicle structure vs. the program plan, funding vs. budget, and the expected • Advanced heat exchangers and heat-transfer fluids future accomplishments vs. the program plan. —Innovative, enhanced airside heat-rejection concepts —New materials, such as carbon foams, for cooling System changes for heavy duty trucks are always compli- system components cated by the fact that truck manufacturers are assemblers of —Nanofluids for improving heat transfer properties of components specified by the truck buyer. As such, coopera- coolants and engine oils tive engineering design and development relationships may —Mitigation of heat exchanger fouling not exist between the suppliers of the many different compo- • Advanced thermal management concept development nents assembled into the thermal management system. The —Heat pipes engine supplier may specify the thermal loading requirement —Cooling by nucleate-boiling for radiators, after coolers, oil coolers, and the controls to —Waste-heat recovery (e.g., thermoelectric generators) manage their interactions. • Simulation code development Since the combinations of component characteristics and —CFD for airflow and temperatures of the powertrain, controls required to optimize such systems may span the under-hood aerodynamics and airflow, lubricant cool- capabilities of many supply companies, it may be necessary ing, vehicle-load predictions, cooling systems, and for DOE to sponsor new sets of relationships to attack these control systems problems. Many of the suppliers required for such a coopera- —Experimental database tive effort are not presently participants in the 21CTP. • Thermal signature management (the committee assumed On the other hand, several elements in the thermal man- that this area was focused on military applications) agement systems, such as water and oil pumps, are key —Masking technologies to mask overall signature items in meeting engine life and reliability goals for the —Masking technologies to mask specific cargoes engine manufacturers. These components are matched to the engine to meet torque, speed, cylinder pressure and thermal Finding 5-4. The committee noted that the above list of research areas was extensive and comprehensive. However, Rogelio Sullivan, DOE, “Parasitic Energy Loss Reduction,” Presentation the list appeared to be significantly more ambitious than the to the committee, Washington, D.C., February 8, 2007, Slide 5. 

78 REVIEW OF THE 21ST CENTURY TRUCK PARTNERSHIP load requirements. As such, the capacity and power use of 1. Engine efficiency. Improved friction and piston/ring the systems, which are usually direct drive from the engine, lubrication can improve engine efficiency. probably exceed the real requirements at speeds and loads 2. Driveline components (transmission, axles, etc.). away from the torque peak maximum load condition. This Advances in lubrication and friction can reduce the fact means that potential for system efficiency improvements losses in driveline components. may exist over a good portion of the engine operating map. 3. Engine emissions and aftertreatment systems. Lubri- Currently the engine builders use very reliable belt and gear cant formulations and coatings can impact exhaust drives for oil and water pumps to meet engine life and reli- p ­ articulate matter as well as exhaust sulfur and ability goals. If newly developed systems such as variable phosphorous content, which can affect exhaust after­ speed drives with flexible controls are to be engineered in treatment systems. the truck systems, the long-term durability and reliability of the systems will have to be demonstrated to engine builders The 21CTP roadmap (DOE, 2006a, p. 1) states that the and truck buyers. These development demonstrations will long-term objective of this goal is the development of tools be costly and take many years to complete. The Caterpillar and technology to reduce parasitic friction losses in the “More Electric Truck” project and presentations by ­Cummins engine, driveline and auxiliary components. The following indicated that the engine manufacturers have begun to think barriers and challenges in friction and wear reduction were along such lines but the present state of progress was difficult identified: for the committee to assess. • Although reducing the viscosity of drivetrain fluids Finding 5-6. The achievement of present program targets will reduce viscous and windage losses, current would require the involvement of a wide range of new pro- designs, materials, and lubricant additives are inad- gram participants and the sharing of responsibilities among equate to maintain component durability and reliability new program partners, inherently incorporating higher when used with low-viscosity fluids. technical and durability risks than the present approaches. • The current levels of phosphorous-based additives Truck manufacturers are assemblers of components specified (ZDDPs) used in engine lubricants will rapidly by the truck buyer, and cooperative design and development degrade the performance of emission-control devices. relationships may not exist between suppliers. However, reducing the level of phosphorous and other metal-containing additives will accelerate the wear of Recommendation 5-6. DOE should determine if the above critical engine components and degrade engine dura- approach for achieving Goal 4A is feasible within the scope bility and reliability. Thus, a delicate balance must be of the 21CTP and containable within the available budget. maintained. DOE should take a strong leadership role with appropriate • Cost-effective technologies for high-volume manufac- funds to bring manufacturers and suppliers together for sys- turing of low-friction, wear-resistant materials, surface tems research and development for Goal 4A and Goal 3. treatments, and additives are lacking. • Integration of component designs with advanced mate- rials, engineered surfaces, and lubricants into complete GOAL 4B: THERMAL MANAGEMENT and FRICTION systems is poor. AND WEAR—DEVELOP AND DEMONSTRATE TECHNOLOGIES THAT REDUCE POWERTRAIN AND The following major topics addressing both short-term and DRIVELINE LOSSES BY 50 PERCENT, THEREBY long-term friction, wear, and lubrication technologies were IMPROVING CLASS 8 FUEL EFFICIENCIES BY 6 TO 8 identified by DOE and industry for improving fuel economy, PERCENT while maintaining system durability and reliability: The background and approach for Goal 4B were also described in the 21CTP Roadmap and Technical White • Integration of mechanistic friction and wear models Papers (DOE, 2006a) as discussed and summarized below. into codes to predict and mitigate parasitic energy Friction, wear and lubrication are important considerations losses in many approaches for reducing energy consumption. Con- • Advanced materials and coating technologies that sequently, DOE identified the following opportunities for lower friction, reduce wear and improve reliability improvements: • Engineering surfaces to improve friction and lubrica- tion properties • Lubricant additives • Boundary layer lubrication studies to control friction, durability and reliability Vinod K. Duggal, Cummins Engine Company, Inc., “Diesel Engine R&D and Integration,” Presentation to the committee, Washington, D.C., February 9, 2007, Slide 8. 

PARASITIC LOSSES OF ENERGY 79 Finding 5-7. The committee noted that the DOE list of engine (Heywood, 1988, p. 724), the friction losses research topics in friction, wear and lubrication was exten- were estimated by the committee to be approximately sive and comprehensive. However, the list appeared to be 30 kW. The goal of a 50 percent reduction in engine significantly more ambitious than the budget for the 21CTP friction would reduce the total fuel energy used by 15 could fund. The committee assumes that this was the case kW (from a total fuel energy used of 380 kW), which since no projects or results from any of the above research would reduce fuel consumption by 3.7 percent. areas were provided. The above insights indicate that, even if DOE can achieve Recommendation 5-7. In addition to identifying a list of a 50 percent reduction in powertrain and drivetrain losses, topics addressing friction, wear, and lubrication technolo- a reduction in fuel consumption of only 5 percent (sum of gies, DOE should develop, fund and implement plans for 1.2 percent for drivetrain and 3.7 percent for powertrain) pursuing key areas that will lead to the successful accom- could be achieved. This is a shortfall relative to the goal of plishment of the specific 21CTP Goal 4B. DOE’s first step 6-8 percent. should be to conduct detailed friction testing of a range of Furthermore, the engineering details of achieving 50 per- heavy-duty diesel engines, transmissions, and final drives to cent reduction in driveline and engine losses were not determine those with best-in-class friction. With respect to provided to the committee. However, past experience has engines, previous industry light- and heavy-duty engine fric- indicated that major reductions in powertrain and drivetrain tion reduction investigations that included lightweight-low losses have not been achievable while retaining adequate friction piston and piston ring designs, low friction coat- durability and reliability. The committee concluded that ings and surface finishes, reduced engine bearing sizes and due to the lack of an in-depth technical rationale and a plan other design modifications should be reviewed to determine to approach the goal, it is very unlikely that this goal can opportunities for reducing engine friction below best-in-class be achieved. The issues with the basis for calculating the levels. From this assessment, other candidate technologies percentage improvement must be resolved so that a realistic with the highest potential for meeting the requirements of the reduction in powertrain losses can be determined. engine portion of Goal 4B should be identified. Likewise, the Having noted the above issues with this goal, the com- efficiencies of transmissions and final drives on heavy-duty mittee was concerned that “Track and laboratory tests met or trucks should be measured and compared with the efficien- exceeded goals, validation test is underway.” A description cies of best-in-class light-duty vehicles, normalized for load of the track and laboratory tests that had been performed, differences, thereby providing insight for friction reductions the engineering details and the results from these tests, or in heavy-duty truck transmissions and final drives. From this a description and timetable for the validation test which assessment, other candidate technologies with the highest was reported to be under way were not described for the potential for meeting the requirements of the driveline por- committee. tion of Goal 4B should be identified. While the problems dealing with friction and wear inside the engine can be addressed by engine manufacturers asso- The committee was not provided with the detailed ciated with the 21CTP, the issues associated with the other approach and plans to achieve a 50 percent reduction in driveline devices must be handled by other suppliers that parasitic losses in the powertrain and driveline, which are not currently participants in the 21CTP. Here again, the would yield a 6 to 8 percent improvement in fuel efficiency. makeup of the truck building industry makes the required However, some insights into this goal were provided by cooperative efforts difficult. The fact that the truck build- reviewing the following information, which was available ers use components specified by the truck end-users means to the committee: that the driveline efficiency responsibility may be shared by several manufacturers. A review of specifications on drive- 1. Driveline losses. DOE has a target for reducing drive- line components indicated that, although torque and speed train losses from 9 kW (Table 5-1) by 50 percent to specifications were readily available, specifications regard- 4.5 kW. Reducing the fuel energy used by 4.5 kW ing power losses were not easily obtained. Thus, buyers pres- (from a total fuel energy used of 380 kW as shown ently make such decisions absent of efficiency information. in Figure 3-1) would reduce fuel consumption by Since lubricant viscosity and additives will have an impact 1.2 percent. on both the efficiency and life of the driveline components, 2. Powertrain losses. Baseline engine losses are shown decisions will have to be made carefully so as not to reduce to be 220 kW in the energy audit of a typical Class driveline component life as efficiency is improved. Changes 8 tractor-trailer combination at 65 mph road load to driveline systems will have to demonstrate life character- (Figure 3-1). A further breakdown of these losses into istics similar to those that exist today, thus the introduction coolant loss, exhaust heat loss and friction loss was not provided to the committee. However, by using Rogelio Sullivan, DOE, “Parasitic Energy Loss Reduction,” Presentation a typical FMEP value for a direct injected diesel to the committee, Washington, D.C., February 8, 2007, Slide 5. 

80 REVIEW OF THE 21ST CENTURY TRUCK PARTNERSHIP of such systems will be costly and require several years of rolling resistance. However, of the mechanical energy needed life validation demonstration. to maintain the truck at speed arising from auxiliary loads, The improvement of driveline efficiencies presents a sig- drivetrain losses, aerodynamic losses, and rolling resistance, nificant problem for DOE. The required involvement of new rolling resistance constitutes 32 percent of the total. Thus, suppliers and the costly requirement to demonstrate long- at stake is a loss equivalent to about one-third of the power lived components may be beyond DOE’s budget limits. needed to propel the truck. Consequently, the initial goal for a 10 percent reduction in rolling resistance at the outset of Finding 5-8. In contrast to the report by DOE to the com- the Partnership would be expected to achieve a reduction in mittee, the analysis of the basis of this goal by the committee fuel consumption of about 3 percent. In terms of fuel sav- indicates that it is very unlikely that this goal can be achieved ings at the national level, this 3 percent can be translated within the scope of the 21CTP. The achievement of the into gallons of fuel if it is assumed that the engine losses goal’s projected fuel savings appears to be very unlikely with decrease in proportion to the reduction in power required. accompanying high risks relative to component life. Using the Federal Highway estimate (DOE, 2006a, p. 5) that tractor-trailers consume 26.8 billion gallons of fuel Recommendation 5-8. DOE should reassess the basis of this a ­ nnually, the savings would be about 800 million gallons per goal and determine if 50 percent reductions in powertrain year just for tractor-trailers. For smaller trucks used in other and drivetrain losses are technically feasible. Based on this vocational applications the savings are not well known, but assessment of technical feasibility, DOE should determine if are likely to be on the same order of magnitude. At the pas- this goal should be pursued based on its potential fuel sav- senger car level it has been estimated (NRC, 2006, p. 4) that ings vs. other competing programs within the 21CTP. If DOE a 10 percent reduction in rolling resistance would translate determines that this goal should be pursued, they should then into a fuel savings of 1 to 2 percent. Assuming a nominally develop specific program plans, timing and funding. conservative value of 2 percent savings from a 10 percent reduction in rolling resistance, U.S. petroleum consumption from trucks of class 3 through 8 trucks could be reduced Goal 5: Rolling Resistance Technology by approximately 20 million barrels per year. (Note: This Goal—10 percent Reduction In Tire-Rolling quantity was calculated based on the 2.6-million-barrel-per- Resistance Values Relative To Existing day estimate for the year 2005 shown in the current 21CTP Best-In-Class Standards Without roadmap [DOE, 2006a, Figure 1-2].) Compromising Cost Or Performance Background Suggestions for Government Initiatives Rolling resistance of tires is one of the parasitic losses In the highly competitive tire market, the technology acting on trucks that increase fuel consumption. Although by which tires are designed to have specific attributes is rolling resistance is generally considered a tire property, it is proprietary to the manufacturers. Thus the opportunity for also recognized to be dependent on the texture and rigidity government agencies to develop partnerships and partici- of the road surface. The 21CTP initially considered rolling pate in developing improved tires is limited. Thus, it is not resistance to be one of the areas warranting investigation surprising that no tire manufacturers participated as partners inasmuch as it is estimated to consume about 51 kW of power in the 21CTP. during highway travel of a fully loaded Class 8 truck (DOE, Designing tires for low rolling resistance is often in con- 2006a, Table 3.1). The Partnership set a goal for 10 percent flict with other performance objectives and hence falls under reduction relative to existing best-in-class standards (DOE, the purview of tire manufacturers. For example, using low- 2006a, Section 3.2). However, it failed to become an active hysteresis materials in the tread to reduce rolling resistance area of investigation with the result that there has been little directly conflicts with the need for tread hysteresis in order to attention or discussion within the program. maintain good wet traction. Similarly, reducing tread depth also reduces rolling resistance but at the cost of decreased tire life. Numerous other conflicts exist. Significance of Rolling Resistance Recognizing that there is little opportunity for govern- The 21CTP estimate of 51 kW of power to overcome ment agencies to participate in developing tire technologies, rolling resistance of an 80,000 lb Class 8 truck operating at the question arises as to whether there is any mechanism 65 mph on a level road corresponds to a rolling resistance for encouraging development and adoption of performance force that is 0.6 percent of the vehicle weight. Of the total standards for rolling resistance. The industry itself supports energy consumed (400 kW per hour) 12.75 percent is due to standardization of tire and wheel related components through the Tire and Rim Association, Inc. In existence since 1903, Rogelio Sullivan, DOE, “Parasitic Energy Loss Reduction,” Presentation the Association holds primary responsibility for establishing to the committee, Washington, D.C., February 8, 2007, Slide 5. standards for dimensions, load ratings and inflation pressures 

PARASITIC LOSSES OF ENERGY 81 for tires in the United States, in addition to standards for rim ual truck tires on vehicle fuel consumption; to convey such dimensions, tubes, valves and other components. tire information to both buyers and sellers; and to periodi- Two standard tests for measuring rolling resistance exist cally reassess the effectiveness of this consumer information as SAE recommended practices—SAE J1269, “Rolling and the methods used for communicating it. Resistance Measurement Procedure for Passenger Car, Light Truck, and Highway Truck and Bus Tires” (SAE, 2006) References and SAE J2463, “Stepwise Coastdown Methodology for Measuring Tire Rolling Resistance” (SAE, 1999). Both tests Cooper, Kevin. 2004. Commercial Vehicle Aerodynamic Drag Reduction: Historical Perspective as a Guide. In Proceedings of a Conference on the are conducted in a laboratory with the tire loaded against a Aerodynamics of Heavy Vehicles: Trucks, Buses, and Trains, December 1.7-meter-diameter drum. While these test procedures are not 2-6, 2002. Washington, D.C.: DOE. identical to each other or to on-road operating conditions, DOE (U.S. Department of Energy). 2000. Technology Roadmap for the 21st they can be expected to provide good relative measures of Century Truck Partnership. Document No. 21CTP-001. Washington, rolling resistance. D.C.: DOE, December. DOE. 2004. Proceedings of a Conference on the Aerodynamics of Heavy Since precedent and test procedures exist, the government Vehicles: Trucks, Buses, and Trains, December 2-6, 2002. Washington could add grading requirements for rolling resistance to the D.C.: DOE. UTQGS (Uniform Tire Quality Grading System) if there is DOE. 2006a. 21st Century Truck Partnership Roadmap and Technical White promise of its effectiveness. At least two barriers exist: Papers Doc. No. 21CTP-003. Washington D.C. December. DOE. 2006b. FreedomCAR and Vehicle Technologies Program Multi-Year Program Plan, 2006–2011. Washington D.C.: DOE, EERE. October. • Consumer acceptance—Although the UTQGS was DOE. 2007. 21st Century Truck Partnership, Project Quad Sheets. Doc. No. designed to assist consumers in making informed 21CTP-004. Washington, D.C.: DOE, January. choices when buying passenger car tires, it is not uni- DOE, FCVT. 2005a. Heavy Vehicle Systems Optimization Program, Annual versally effective. The effectiveness was evaluated in Progress Report. Washington D.C.: DOE. Available at http://www1. a 1992 telephone survey of individuals who buy tires eere.energy.gov/vehiclesandfuels/resources/fcvt_mypp.html. Accessed May 14, 2008. for their own vehicles and individuals who buy tires DOE, FCVT. 2005b. Heavy Vehicle Systems Optimization Merit Review for fleets of vehicles (Weiss, 1992). Approximately and Peer Evaluation, Annual Progress Report. Washington D.C.: 80 percent of potential customers considered UTQGS DOE. Available at http://www1.eere.energy.gov/vehiclesandfuels/ information important to a purchase decision, although pdfs/­program/2006_hvso_merit_review.pdf; http://www1.eere.energy. only about 30 percent of recent customers considered gov/vehiclesandfuels/pdfs/program/2005_hvsop_report.pdf Accessed May 14, 2008. it in their last purchase. More than 50 percent of fleet DOE, FCVT. 2006. FY 2006 Annual Progress Report for Heavy Vehicle buyers considered UTQGS information important in Systems Optimization Program, Section I. Aerodynamic Drag Reduc- buying decisions. tion. Washington D.C.: DOE. • Retread tires—More than 50 percent of the tires on Heywood, J. B. 1988. Internal Combustion Engine Fundamentals. McGraw- long-haul trucks are retreads. A retread is simply new HiII Series in Mechanical Engineering. McGraw-Hill. McCallen, R., D. McBride, W. Rutledge, F. Browand, A. Leonard, and J. tread molded on to an existing, pre-used tire carcass. Ross. 1998. A Multi-Year Program Plan for the Aerodynamic Design Rolling resistance depends both on the design and of Heavy Vehicles. UCRL-PROP 127753 Dr. Rev 1, February 1998. materials of the tread stock as well as the under­lying Available at http://www.osti.gov/bridge/servlets/purl/771203-eeW6Mf/­ structure. Thus, each retread will have a different roll- native/771203.pdf. Accessed May 14, 2008. ing resistance value. Therefore, it is less practical to NRC (National Research Council). 2000a. Review of the U.S. Department of Energy’s Heavy Vehicle Technology Program. Washington, D.C. expect rolling resistance values to be measured for National Academy Press. retread tires than for those produced by OEM tire NRC. 2000b. Review of the Research Program of the Partnership for a manufacturers. New Generation of Vehicles. Sixth Report. Washington, D.C.: National Academy Press. Finding 5-9. There is a precedent for government to estab- NRC. 2003. Use of Lightweight Materials in 21st Century Army Trucks. Washington, D.C.: The National Academies Press. lish performance measures for tires as illustrated by the NRC. 2006. Tires and Passenger Vehicle Fuel Economy: Informing Con- Uniform Tire Quality Grading System (UTQGS) adopted sumers, Improving Performance. TRB special report 286. Washington, by NHTSA in 1980 [Part 575.104 of the Consumer Infor- D.C.: The National Academies Press. mation Regulations]. The UTGS applies to passenger car SAE (Society of Automotive Engineers International).1999. Recommended tires and requires manufacturers to grade new tires for tread Practice, “Stepwise Coastdown Methodology for Measuring Tire Roll- ing Resistance,” Doc. No. J2452, June. Available at http://www.sae. wear, wet traction and temperature resistance. Tread wear is org/­technical/standards/J2452_199906. Accessed June 2, 2008. graded on a numerical scale, while traction and temperature SAE. 2006. Recommended Practice, “Rolling Resistance Measurement resistance are graded on an alphabetic scale. There is no Procedure for Passenger Car, Light Truck, and Highway Truck and current requirement for grading rolling resistance, or for Bus Tires,” Doc. No. J1269, September. Available at http://www.sae. grading truck tires. org/technical/standards/J1269_200609. Accessed June 3, 2008. Weiss, Sandra. 1992. “An Evaluation of the Uniform Tire Quality Grading Standards and Other Tire Labeling Requirements.” NHTSA Report Recommendation 5-9. DOE, EPA, and DOT should arrange Number DOT HS 807 805. Washington, D.C.: U.S. Department of to gather and report information on the influence of individ- Transportation, January.