While fuel consumed per mile by light-duty vehicles improved substantially between 1966 and 2007, fuel consumption of the average heavy-duty vehicle remained nearly constant (Figure 1-2). However, this trend hides an important factor regarding trucking. The mission is not just to move the truck and driver from one place to another but to deliver cargo. If total fuel consumed, total miles traveled, and total tons shipped are considered for the United States as a whole, a U.S. average payload specific fuel consumption for the entire medium- and heavy-duty fleet can be calculated for this sector. Figure 1-3 shows the results of dividing the total fuel consumed by the miles traveled and tons moved each year, to produce a fuel consumption per ton shipped and per mile driven (gallon/ton-mile) from 1975 to 2005. The amount of fuel required to move a given amount of freight a given distance has been reduced by more than half over this time period. This is a result of many factors, including:

  • Improved efficiency of engines and drivelines

  • Improved vehicle aerodynamics

  • Improved tire rolling resistance

  • Widespread implementation of electronic control features such as road speed governors

  • Regulatory changes that allowed the use of longer, wider, and taller trailers and higher maximum weight limits

  • Operational efficiency improvements by trucking companies to reduce the amount of distance traveled with little or no load

The improvement trend in this U.S. average payload specific fuel consumption for trucks has slowed in the past several years, at least in part due to the requirement to introduce new pollution controls for EPA-regulated air pollutants such as nitrogen oxides (NOx) and particulate matter (PM). The resulting changes to diesel engines have tended to degrade their thermal efficiency. Gasoline engines also suffered degradation in performance when first required to meet regulated emission standards. The development of the three-way catalyst has allowed the recapture of much of the

FIGURE 1-2 Motor vehicle mileage, fuel consumption, and fuel rates. SOURCE: DOE, EIA (2009a, Figure 2.8).

FIGURE 1-2 Motor vehicle mileage, fuel consumption, and fuel rates. SOURCE: DOE, EIA (2009a, Figure 2.8).

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