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Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles (2010)

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

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Suggested Citation:"Appendix E: Fuel Economy and Fuel Consumption as Metrics to Judge the Fuel Efficiency of Vehicles." Transportation Research Board and National Research Council. 2010. Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/12845.
×

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.

Suggested Citation:"Appendix E: Fuel Economy and Fuel Consumption as Metrics to Judge the Fuel Efficiency of Vehicles." Transportation Research Board and National Research Council. 2010. Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/12845.
×

The following equations hold for calculating FE and FC:.

The equations above hold from engine on to engine off in order to capture idle time. Chapter 2 refers to an “average payload” to calculate load-specific fuel consumption (LSFC) but does not indicate how to calculate it on a trip delivering cargo. The calculation for average payload is as follows:

where Px = payload in tons carried for time x when the vehicle is moving, and tx = time in hours carrying payload Px. This is a “time average payload” for a vehicle operating in the field and excludes idle time—it is the integral of payload to get the average payload.

From Figure 2.6, LSFC does not decrease significantly for a payload increase as long as the payload is greater than 70 percent of the full payload.

In the equation for payload, if any Px is zero, there is zero in the numerator for that segment, but the time is counted in the denominator, which then lowers the average payload. The FC during the no-load segment would decrease, lowering the total gallons of fuel used. If the time average payload is less than 70 percent of full load, LSFC will increase—if it is greater than 70 percent, LSFC will increase somewhat based on Figure 2.6.

Then,

and the

Therefore,

For picking up cargo, the average payload equation would need a plus payload term for each segment to account for the pickup. Therefore, P2 = P1Pd + Pp where Pd = payload delivered and Pp = payload picked up after segment 1,

TABLE E-1 Gross Vehicle Weight Groups

Group

Gross Vehicle Weight (lb)

1

<6,000

2

6,001-10,000

3

10,001-14,000

4

14,001-16,000

5

16,001-19,500

6

19,501-26,000

7

26,001-33,000

8

>33,000

NOTE: Vehicle groups used for average payloads in Tables E-2 and E-3.

SOURCE: Development of Truck Payload Equivalent Factor (TPEF), final report submitted to Office of Freight Management and Operations, Federal Highway 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.

Suggested Citation:"Appendix E: Fuel Economy and Fuel Consumption as Metrics to Judge the Fuel Efficiency of Vehicles." Transportation Research Board and National Research Council. 2010. Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/12845.
×

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: Development of Truck Payload Equivalent Factor (TPEF), final report submitted to Office of Freight Management and Operations, Federal Highway 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.

Suggested Citation:"Appendix E: Fuel Economy and Fuel Consumption as Metrics to Judge the Fuel Efficiency of Vehicles." Transportation Research Board and National Research Council. 2010. Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/12845.
×

TABLE E-3 Vehicle Groups and National Average Payload (lb)

Major Body Type

Group 1

Group 2

Group 3

Group 4

Group 5

Group 6

Group 7

Group 3

Truck or Truck + Trailer

 

 

 

 

 

 

 

 

Bulk

-

6,249

4,798

5,004

10,831

13,152

15,707

30,966

Flatbed

*

4,027

4,767

4,858

7,836

9,465

11,405

16,693

Tank

-

6,077

4,438

7,266

7,249

12,991

15,743

26,858

Van

*

4,179

3,071

4,322

6,770

7,516

9,519

6,233

Reefer

-

4,320

3,196

4,263

*

9,161

10,983

10,414

Logging

-

15,036

*

*

*

10,787

*

42,857

Other

*

2,969

3,075

4,442

5,235

7,391

11,887

23,853

Tractor + Trailer

 

 

 

 

 

 

 

 

Automobile

-

-

-

-

*

*

25,443

34,257

Livestock

-

-

-

*

-

44,361

27,747

42,535

Bulk

-

*

-

*

-

36,846

45,319

50,135

Flatbed

-

*

*

*

*

24,997

31,949

41,874

Tank

-

-

-

-

-

*

47,656

49,788

Van

-

-

-

-

-

23,995

28,079

38,721

Reefer

-

-

-

-

-

19,390

24,775

41,426

Logging

-

-

-

*

-

*

*

50,004

Other

-

-

-

-

-

*

31,498

31,800

SOURCE: Development of Truck Payload Equivalent 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.freight_analysis/faf/faf2_reports/reports9/index.htm#toc.

Suggested Citation:"Appendix E: Fuel Economy and Fuel Consumption as Metrics to Judge the Fuel Efficiency of Vehicles." Transportation Research Board and National Research Council. 2010. Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/12845.
×
Page 215
Suggested Citation:"Appendix E: Fuel Economy and Fuel Consumption as Metrics to Judge the Fuel Efficiency of Vehicles." Transportation Research Board and National Research Council. 2010. Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/12845.
×
Page 216
Suggested Citation:"Appendix E: Fuel Economy and Fuel Consumption as Metrics to Judge the Fuel Efficiency of Vehicles." Transportation Research Board and National Research Council. 2010. Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/12845.
×
Page 217
Suggested Citation:"Appendix E: Fuel Economy and Fuel Consumption as Metrics to Judge the Fuel Efficiency of Vehicles." Transportation Research Board and National Research Council. 2010. Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/12845.
×
Page 218
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Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles evaluates various technologies and methods that could improve the fuel economy of medium- and heavy-duty vehicles, such as tractor-trailers, transit buses, and work trucks. The book also recommends approaches that federal agencies could use to regulate these vehicles' fuel consumption. Currently there are no fuel consumption standards for such vehicles, which account for about 26 percent of the transportation fuel used in the U.S.

The miles-per-gallon measure used to regulate the fuel economy of passenger cars. is not appropriate for medium- and heavy-duty vehicles, which are designed above all to carry loads efficiently. Instead, any regulation of medium- and heavy-duty vehicles should use a metric that reflects the efficiency with which a vehicle moves goods or passengers, such as gallons per ton-mile, a unit that reflects the amount of fuel a vehicle would use to carry a ton of goods one mile. This is called load-specific fuel consumption (LSFC).

The book estimates the improvements that various technologies could achieve over the next decade in seven vehicle types. For example, using advanced diesel engines in tractor-trailers could lower their fuel consumption by up to 20 percent by 2020, and improved aerodynamics could yield an 11 percent reduction. Hybrid powertrains could lower the fuel consumption of vehicles that stop frequently, such as garbage trucks and transit buses, by as much 35 percent in the same time frame.

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