E
Fuel Economy and Fuel Consumption as Metrics to Judge the Fuel Efficiency of Vehicles

Figure E-1 shows the relationship of fuel consumption versus fuel economy. The negative slope and the shape of this relationship are both important. The slope of the fuel consumption/fuel economy (FC/FE) curve indicates the amount of change in FC relative to a change in FE. For example, when the slope magnitude in Figure E-1 is high, such as at 10 mpg, there is a large change in FC for a small change in FE. On the other hand, at 50 mpg, there is a small change in FE, since the slope magnitude is very low and approaching zero as indicated by the lower right-hand slope scale on Figure E-1.

FIGURE E-1 Fuel consumption (FC) versus fuel economy (FE) (upper half of figure) and slope of FC/FE curve (lower half of figure). The light-colored lower curve matches the left-hand y-axis, while the dark curve matches the right-hand y-axis.

FIGURE E-1 Fuel consumption (FC) versus fuel economy (FE) (upper half of figure) and slope of FC/FE curve (lower half of figure). The light-colored lower curve matches the left-hand y-axis, while the dark curve matches the right-hand y-axis.

Fuel consumption decreases slowly after 40 mpg since the slope of the FC/FE curve approaches zero (Figure 2-1 lower curve and right-hand scale). The slope rapidly decreases past 40 mpg since it varies as the inverse of FE squared, which then results in a small decrease in FC for large FE increases. This fact is very important since fuel consumption is the metric in corporate average fuel economy (CAFE) standards for light-duty vehicles. For example, the fuel consumption is 2.5 gallons/100 miles at 40-mpg and 1.25 gallons/100 miles at 80 mpg. Thus, a 40 mpg change in fuel economy results in a change in fuel consumption of only 1.25 gallons/100 miles. In going from 8 to 9 mpg, there is a change in fuel consumption of approximately 1.39 gallons/100 miles. This means that a change from 8 to 9 mpg saves more fuel than a change from 40 to 80 mpg. This nonlinear relationship between fuel economy and fuel consumption has important meaning for regulations, where a reduction in fuel use or in greenhouse emissions is desired. Improving vehicles with high fuel consumption (low mpg) and high vehicle miles traveled (VMT) has much more effect on fuel savings than improving low-consumption (high-mpg) and low-VMT vehicles.

Tables E-1, E-2, and E-3 show vehicle groups and national average payload data that can serve as the basis for National Highway Traffic and Safety Administration (NHTSA) use in determining payloads to be used for testing and simulating any future medium- and heavy-duty vehicle fuel consumption procedures as related to standards. The data in Tables E-1 through E-3 and other data in the report on which the tables are based merit careful study by NHSTA before they are considered for use in a regulation.



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E Fuel Economy and Fuel Consumption as Metrics to Judge the Fuel Efficiency of Vehicles Figure E-1 shows the relationship of fuel consumption Fuel consumption decreases slowly after 40 mpg since the versus fuel economy. The negative slope and the shape of this slope of the FC/FE curve approaches zero (Figure 2-1 lower relationship are both important. The slope of the fuel con - curve and right-hand scale). The slope rapidly decreases past sumption/fuel economy (FC/FE) curve indicates the amount 40 mpg since it varies as the inverse of FE squared, which of change in FC relative to a change in FE. For example, then results in a small decrease in FC for large FE increases. when the slope magnitude in Figure E-1 is high, such as at This fact is very important since fuel consumption is the 10 mpg, there is a large change in FC for a small change in metric in corporate average fuel economy (CAFE) standards FE. On the other hand, at 50 mpg, there is a small change for light-duty vehicles. For example, the fuel consumption is in FE, since the slope magnitude is very low and approach- 2.5 gallons/100 miles at 40-mpg and 1.25 gallons/100 miles ing zero as indicated by the lower right-hand slope scale on at 80 mpg. Thus, a 40 mpg change in fuel economy results Figure E-1. in a change in fuel consumption of only 1.25 gallons/100 miles. In going from 8 to 9 mpg, there is a change in fuel consumption of approximately 1.39 gallons/100 miles. This means that a change from 8 to 9 mpg saves more fuel than a change from 40 to 80 mpg. This nonlinear relationship between fuel economy and fuel consumption has important meaning for regulations, where a reduction in fuel use or in greenhouse emissions is desired. Improving vehicles with high fuel consumption (low mpg) and high vehicle miles traveled (VMT) has much more effect on fuel savings than improving low-consumption (high-mpg) and low-VMT vehicles. ∑ n Nn 1 1 1 ∑ n + … + Nn N1 FE1 FEn 1 Tables E-1, E-2, and E-3 show vehicle groups and national average payload data that can serve as the basis for National Highway Traffic and Safety Administration (NHTSA) use in determining payloads to be used for testing and simulating any future medium- and heavy-duty vehicle fuel consump- tion procedures as related to standards. The data in Tables FIGURE E-1 Fuel consumption (FC) versus fuel economy (FE) E-1 through E-3 and other data in the report on which the (upper half of figure) and slope of FC/FE curve (lower half of fig- tables are based merit careful study by NHSTA before they ure). The light-colored lower curve matches the left-hand y-axis, Figure E-1 hile the dark curve matches vs.right-hand y-axis. FCFE curve.epsconsidered for use in a regulation. w Fuel consumption the and slope of are bitmap--legibility is degraded 

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 TECHNOLOGIES AND APPROACHES TO REDUCING THE FUEL CONSUMPTION OF MEDIUM- AND HEAVY-DUTY VEHICLES The following equations hold for calculating FE and Then, FC: Total payload moved on trip from time 0 to tx = P1 − Px, tons miles t Total miles traveled = ∫ dt. hour 0 and the 100 Payload delivered in Segment 1 = P1 − P2, tons, etc. FC = , gallons/100 miles. FE Therefore, The equations above hold from engine on to engine off in order to capture idle time. Chapter 2 refers to an “average Total gallons used × 100 Trip average LSFC = payload” to calculate load-specific fuel consumption (LSFC) Pae × Total miles traveled but does not indicate how to calculate it on a trip delivering cargo. The calculation for average payload is as follows: For picking up cargo, the average payload equation would need a plus payload term for each segment to account for P1t1 + P2 t2 + … Px t x Average payload = = Pae the pickup. Therefore, P2 = P1 – Pd + Pp where Pd = payload t1 + t2 + …t x delivered and Pp = payload picked up after segment 1, where Px = payload in tons carried for time x when the ve- hicle is moving, and tx = time in hours carrying payload Px. TABLE E-1 Gross Vehicle Weight Groups This is a “time average payload” for a vehicle operating in Group Gross Vehicle Weight (lb) the field and excludes idle time—it is the integral of payload 1 <6,000 to get the average payload. 2 6,001-10,000 From Figure 2.6, LSFC does not decrease significantly 3 10,001-14,000 for a payload increase as long as the payload is greater than 4 14,001-16,000 70 percent of the full payload. 5 16,001-19,500 In the equation for payload, if any Px is zero, there is zero 6 19,501-26,000 7 26,001-33,000 in the numerator for that segment, but the time is counted in 8 >33,000 the denominator, which then lowers the average payload. The NOTE: Vehicle groups used for average payloads in Tables E-2 and E-3. FC during the no-load segment would decrease, lowering SOURCE: Deelopment of Truck Payload Equialent Factor (TPEF), final the total gallons of fuel used. If the time average payload is report submitted to Office of Freight Management and Operations, Federal less than 70 percent of full load, LSFC will increase—if it is Highway Administration, Washington, D.C., by Battelle, 505 King Avenue, greater than 70 percent, LSFC will increase somewhat based Columbus, Ohio 43201. June 15, 2007. Available at http://ops.fhwa.dot. on Figure 2.6. gov/freight/freight_analysis/faf/faf2_reports/reports9/index.htm#toc.

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 APPENDIX E TABLE E-2 Average Payload (lb) by Commodities and Gross Vehicle Weight Group VIUS—National Commodities Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 Live animals and fish - 5,055 7,638 5,424 9,472 17,200 16,345 40,022 Animal feed or products of animal origin - 4,682 6,138 3,760 8,330 11,778 18,980 39,841 Cereal grains - 13,348 15,234 8,690 14,334 17,640 24,208 41,922 All other agricultural products - 10,728 6,889 5,985 7,660 11,348 26,793 34,616 Basic chemicals - * * 3,386 * 11,180 14,264 38,431 Fertilizers and fertilizer materials - 8,062 2,937 5,382 7,898 12,308 25,148 30,134 Pharmaceutical products - * * - * 7,455 * 14,507 All other chemical products - 2,715 3,046 4,357 6,193 9,712 17,574 36,411 Alcoholic beverages - - 2,670 - * 16,177 20,142 35,758 Bakery and milled grains - 2,000 2,407 7,083 * 3,198 27,732 31,389 Meat, seafood, and their preparation - * 10,402 3,646 - 8,819 10,738 40,012 Tobacco products - - 2,700 - - * 9,253 34,381 All other prepared foodstuff - 4,354 3,607 3,617 5,486 13,240 23,736 38,894 Logs and other wood in rough - 5,838 4,880 * 9,384 11,029 22,746 46,774 Paper and paperboard articles - - * - 6,718 8,842 18,591 37,932 Printed products - 8,864 3,418 4,699 2,126 8,578 8,805 21,340 Pulp, newsprint, paper, or paperboards - * * * - 10,904 15,815 41,774 Wood products - 3,303 3,592 5,410 7,263 8,218 16,182 34,699 Articles of base metal * 1,808 2,016 4,399 4,323 8,095 12,840 29,564 Base metal finished or semi-finished form * 3,375 3,871 3,731 4,080 6,356 12,110 38,010 Non-metallic mineral products - 3,737 2,088 3,438 6,652 10,527 28,977 35,962 Non-powered tools - 2,675 3,167 4,353 5,421 6,680 9,899 14,810 Powered tools - 3,894 3,602 4,849 8,513 7,405 12,242 25,241 Electronic and other electrical equipment - 2,463 4,068 2,060 * 7,877 9,946 26,353 Furniture, mattresses, lamps, etc. - 2,056 2,769 2,591 - 6,397 17,501 22,598 Machinery - 4,271 4,277 9,265 5,020 9,958 17,598 35,754 Miscellaneous manufactured products - 1,401 2,411 6,148 5,615 8,571 17,861 27,236 Precision instruments and appliances - 1,455 1,373 10,095 - 4,391 * 26,195 Textile, leather, and related articles - 2,073 2,986 * 8,701 7,599 41,925 36,656 Vehicle, including parts - 3,751 5,506 5,896 7,333 8,173 23,554 31,945 All other transportation equipment - - 2,025 5,431 * 16,312 18,286 42,517 Coal - * * - - 6,748 - 50,011 Crude petroleum - - - - - 8,590 - 39,890 Gravel and crushed stones - 6,544 6,931 6,276 10,122 13,770 24,305 39,130 Metallic ores and concentrates - - * - 10,000 - - 42,272 Monumental and building stones - * 3,460 5,782 14,100 10,392 9,473 35,960 Natural sand - 7,306 3,029 12,849 6,000 11,643 28,662 38,067 All other nonmetallic minerals - 7,337 3,064 2,478 7,662 16,262 13,580 38,835 Fuel oils - 4,484 14,811 - * 15,422 17,525 39,634 Gasoline and aviation turbine - * - 2,825 - 15,128 18,916 53,423 Plastic and rubber - * 2,931 3,329 * 8,113 12,548 30,379 All other coal and refined petroleum - 4,519 4,336 * 4,874 10,326 18,672 41,027 Hazardous waste - * 1,500 - - 6,854 15,517 37,856 All other waste and scrap - 3,384 2,927 * 5,951 8,120 12,823 24,944 Recyclable products - 3,153 4,878 3,689 * 8,425 13,743 27,532 Mail and courier parcels * 7,976 5,559 4,608 7,342 10,884 33,344 31,628 Empty shipping containers - 2,661 * - * 2,309 16,129 26,699 Passengers - 2,264 2,501 * * * * * Mixed freight - 2,080 2,633 4,051 * 20,137 28,811 37,094 Multiple categories - 3,602 3,375 4,198 5,463 8,127 17,189 31,946 Products not classified, blank, not reported or applicable - 2,471 * 6,556 7,809 11,622 17,644 30,545 SOURCE: Deelopment of Truck Payload Equialent Factor (TPEF), final report submitted to Office of Freight Management and Operations, Federal High - way Administration, Washington, D.C., by Battelle, 505 King Avenue, Columbus, Ohio 43201. June 15, 2007. Available at http://ops.fhwa.dot.gov/freight/ freight_analysis/faf/faf2_reports/reports9/index.htm#toc.

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 TECHNOLOGIES AND APPROACHES TO REDUCING THE FUEL CONSUMPTION OF MEDIUM- AND HEAVY-DUTY VEHICLES TABLE E-3 Vehicle Groups and National Average Payload (lb) SOURCE: Deelopment of Truck Payload Equialent Factor (TPEF), final report submitted to Office of Freight Management and Operations, Federal High - way Administration, Washington, D.C., by Battelle, 505 King Avenue, Columbus, Ohio 43201. June 15, 2007. Available at http://ops.fhwa.dot.gov/freight/ freight_analysis/faf/faf2_reports/reports9/index.htm#toc.