FIGURE 8-1 Shared responsibility for major elements that affect heavy-duty-vehicle fuel efficiency. SOURCE: Bradley and Associates (2009).

FIGURE 8-1 Shared responsibility for major elements that affect heavy-duty-vehicle fuel efficiency. SOURCE: Bradley and Associates (2009).

  • Methods for certification and compliance. What methods will be used to determine compliance and overall program effectiveness?

  • Regulatory model.

REGULATED VEHICLE TYPES

The committee has considered a broad range of vehicles. These include pickup trucks, transit buses, motor coaches, school buses, delivery vans, straight trucks, and combination vehicles such as tractor trailers. The largest fuel use from the heavy-truck fleet is associated with the vehicles that move the vast majority of the freight: Class 8 tractor trailers with gross combined weight (GCW) ranging from 80,000 lb on the interstate and in excess of 130,000 lb on some state highways (GCW varies considerably, as it is governed by federal and state size and weight regulations). This is not surprising, considering the huge jump in weight hauling capacity between Class 8 (in excess of 130,000 lb) and the rest of the heavy-duty fleet (Class 2b through 7 weight capacity ranges from 8,500 to 33,000 lb). Class 8s are about 20 percent of the fleet in total number of vehicles, but 61 percent of the fuel use of all heavy-duty vehicles. The second largest fuel use segment is the Class 2B, which makes up the majority of heavy-duty vehicles (53 percent) and which is responsible for just under 20 percent of fuel consumption. The third largest class is Class 6. These are considered medium heavy-duty and generally have only a single rear axle, while Class 8 vehicles typically have tandem drive axles. Class 6 vehicles make up about 16 percent of the heavy truck population and consume 11 percent of the fuel. Table 8-1 gives more detail.

Most Class 8 vehicles are combination trucks for which several trailer options are available to complete the vehicle system (see Figure 8-2), adding another dimension to an already complex regulatory challenge. For example, the type of trailer used will influence the vehicle’s overall aerodynamic drag coefficient and the projected frontal area, both of which influence aerodynamic losses and directly affect fuel consumption. The tires, on both the tractor and the trailer, will influence the rolling resistance. In addition, weight and dimension regulations define the “legal” GVW, which also influences fuel consumption. An added complication is that the size and weight regulations for a given vehicle vary depending on the jurisdiction—federal or state.

The problems are compounded further in that vehicles

TABLE 8-1. Mileage and Fuel Consumption by Vehicle Weight Class

Vehicle

Population (millions)

Annual Miles (million)

Annual Fuel Use (million gallons)

Percent of Population

Percent of Annual Miles

Percent of Fuel Use

Class 2B

5.800

76,700

5,500

52.8

35.1

19.3

Class 3

0.691

9,744

928

6.3

4.5

3.3

Class 4

0.291

4,493

529

2.6

2.1

1.9

Class 5

0.166

1,939

245

1.5

0.9

0.9

Class 6

1.710

21,662

3,095

15.6

9.9

10.9

Class 7

0.180

5,521

863

1.6

2.5

3.0

Class 8

2.154

98,522

17,284

19.6

45.1

60.8

Total

10.992

218,580

28,444

100.0

100.0

100.0

SOURCE: DOT (2002).



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