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The Influence of Weight Average model weight of light-duty gas vehicles and trucks Freight-ton miles per heavy-duty diesel truck Data comes from Appendix H-1 of the EPA report (Ref.1.a) Conversion from cars, vans, SUVs, and pickup trucks to the ‘light-duty gas vehicles and trucks’:

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the influence of weight

The Influence of Weight

Average model weight of light-duty gas vehicles and trucks

Freight-ton miles per heavy-duty diesel truck

source for weight data
Data comes from Appendix H-1 of the EPA report (Ref.1.a)

Conversion from cars, vans, SUVs, and pickup trucks to the ‘light-duty gas vehicles and trucks’:

Weight of Light-duty gasvehicles = data for passenger cars only

Weight of Light-duty gas trucks = data for vans, SUVs, and pickup trucks only

Weight data based on inertia weight class (ref1.b)

Curb weight + 300lb for vehicles up to and including 3000 lb

(measured at 250 lb increments)

Curb weight + 500 lb for heavier than 3000 lb (measured at 500 lb increments)

Average weight based on fraction of number of cars sold (Ni) for a weight class (Wi) out of the total number sold that year (NT)

∑i=1(Ni*Wi)/∑NT

Source for Weight Data

Ref. 1.a & 1.b

analyzing weight trends

Analyzing Weight Trends

4 main parts to

Light-duty Gas Weight

Vehicles and trucks weighed the same in 1975

Vehicles weighed less than trucks after 1975

Both vehicles and trucks dropped their respective weights in 1980s

Both vehicles and trucks increased their respective weights from the 1990s to current

Fig. 1: Weight data collected from the EPA; Ref. 1.a.

difference between light duty gas vehicles and trucks
Difference between light-duty gas vehicles and trucks
  • Vehicles and Trucks weighed the same in 1975
    • Initially, light-duty gas vehicles were as heavy as trucks because of no standards for safety or emissions yet

2. Average weight of vehicles lighter than trucks after 1975

    • Reasons for classification of light-duty gas truck

(as not a light-duty gas vehicle):

      • Mainly for commercial and agricultural work
      • Few of them
      • Significant because regulated less strictly under:
        • Energy Policy and Conservation Act for fuel economy
        • Clean Air Act for emissions standards

Ref. 2

weight increase and decrease
Weight Increase and Decrease
  • Influence on weight decrease(1975-late 1980’s)
    • CAFÉ
      • Govt. policy to increase fuel efficiency in 1975(Ref. 3)
    • FMVSS
      • no safety changes from 1974 -1986 (Ref. 5)
  • Influence on weight increase(late 1980’s – 2004)
    • FMVSS
      • Increase in weight of safety equipment (Ref. 5)
    • Technology
      • Used to increase weight and acceleration (Ref. 4)
caf corporate average fuel economy
CAFÉ Corporate Average Fuel Economy

Weight change in cars has little effect on overall fuel efficiency:

  • Due to: Energy Policy and Conservation Act (EPCA)
  • Fuel economy from technology,
  • not small cars:
    • 14 MPG in 1974 to 28.2 MPG in 1994
    • 12.4 MPG or 87% results from technological improvements to passenger cars
    • 1.6 MPG or 11.5% from weight loss
    • 0.2 MPG or 1.4% from consumers buying smaller cars

Ref. 3

fmvss federal motor vehicle safety standards
FMVSSFederal Motor Vehicle Safety Standards
  • Federal Motor Vehicle Safety Standards (FMVSS)
    • Reverse engineering to find out how much weight was going towards safety
    • Safety includes avoiding crashes, fires, and other hazards, and regulating crashes.
    • Weight in passenger cars changed little from 1974-1986 because no new FMVSS changes
    • Many safety technologies in cars later than in light trucks

Ref. 5

technology improvement weight gain

Technology Improvement = Weight Gain

Technology goes to increase weight and acceleration, not fuel economy

Weight increased 21%

Horsepower increased 79%

Ref. 4

If the 2000 model year light vehicle had the same performance and weight as the 1981 model year, there would have been a 25% higher fuel efficiency

Engineering improvements go to fuel injection systems, engines with more valves, etc.

Ref. 3

ton mpg
Ton-mpg
  • Ton-MPG is the miles per gallon times the weight in tons
  • Tells ability to move weight
  • Also tells about the power train and drive-line efficiency

Ref. 1.a.

  • Even though weight has increased in cars, the miles per gallon has also improved.
  • This signifies that weight alone does not indicate the fuel efficiency of a vehicle
source of freight ton mile data
Source of Freight-Ton Mile Data
  • Data for ton-miles from two different sources
    • 1970-1980 Eno Transportation
    • 1990-2002 BTS (Bureau of Transportation Statistics)
  • Measurements taken in 1970, 1980, 1990, and 1994-2002
    • The years in-between two known values and so were interpolated.
  • Only intercity travel, not all travel over the entire USA
  • Ton-miles in Millions of Miles
  • Careful documentation of freight did not begin until the Commodity Flow Survey in 1993

Ref. 6, 7

freight ton miles
Freight-Ton Miles
  • Amount of freight being transported has increased every year
  • Because the data is interpolated and from the intercity travel only, this graph does not accurately depict all freight travel in every year. However, the graph still reveals that the trend of freight-ton miles over time increased.

Ref. 6 & 7

commodity flow survey
Commodity Flow Survey

Change in fuel economy not due to weight of heavy-duty diesels from 1990-2000

Freight energy efficiency decline 6% by 2000:

* a result of a slow 2% annual growth rate in ton-miles

*rapid annual growth rate of 2.5% in freight energy consumption

*There was no increase in ton-miles per vehicle mile from 1990 -2000

Ref. 8

The average weight per truck did not increase much and yet the fuel efficiency went down. This suggests that the weight carried by the truck is not the reason for the change in fuel efficiency from 1990-2000

Ref. 9

conclusions on weight
Conclusions on Weight
  • Weight affects fuel economy
  • However, the effect of weight changes on fuel economy was small compared to technology changes for light-duty gas vehicles and trucks.
  • More freight is being circulated via trucks in 2002 compared to 1975, but the weight per truck is remaining constant.
references
References
  • 1. "Light-Duty Automotive Technology and Fuel Economy Trends: 1975 Through 2004" (EPA420-R-04-001, April 2004)   840 K PDF, 98 pages. http://www.epa.gov/otaq/fetrends.htm
  • 1.a. APPENDIX H - Data Stratified by Weight Class 121 K PDF (47 pages)
  • 1.b. APPENDIX A - Database Details and Calculation Methods151 K PDF (15 pages)
  • 2. “Sport Utlility Vehicles, Mini-Vans and Light Trucks: An Overview of Fuel Economy and Emissions Standards” (CRS Report for Congress: RS20298, January 2001) by Brent Yacobucci. <http://www.ncseonline.org/NLE/CRSreports/Air/air-32.cfm?&CFID=14609448&CFTOKEN=91022181#Back3>
  • 3. STATEMENT OF CLARENCE M. DITLOW DIRECTOR, CENTER FOR AUTO SAFETY Before the SUBCOMMITTEE on ENERGY AND POWER HOUSE COMMITTEE on COMMERCE Washington DC July 24, 1995 <http://www.autosafety.org/article.php?did=812&scid=77>
  • 4. EPA Access: EPA report number EPA420-S-00-003, web www.epa.gov
  • 5. “Cost and Weight Added by the Federal Motor Vehicle Safety Standards for Model Years 1968-2001 in Passenger Cars and Light Trucks” by Marcia J. Tarbet (NHTSA Report Number DOT HS 809 834,December 2004) <http://www.nhtsa.dot.gov/cars/rules/regrev/evaluate/809834.html>
references15
References
  • 6. Eno Transportation Foundation, Inc., Transportation in America, 2000 (Washington, DC: 2001), p. 12. <http://www.bts.gov/publications/national_transportation_statistics/2004/html/table_truck_profile.html>
  • 7. U.S. Department of Transportation, Bureau of Transportation Statistics, special tabulation, Mar. 11, 2005. http://www.bts.gov/publications/national_transportation_statistics/2004/html/table_truck_profile.html
  • 8. Source: Department of Transportation, Bureau of Transportation Statistics, National Transportation Statistics 2002, tables 1-44, 4-6.
  • 9. ‘Transportation Energy Efficiency Trends in the 1990s” Department of Transportation, Bureau of Transportation Statistics, National Transportation Statistics 2002 <http://www.bts.gov/publications/issue_briefs/number_02/html/transportation_energy_efficiency_trends_in_the_1990s.html>