The measures listed in Table 8-3 address the vehicle task and are based on fuel or energy consumption. This list is not complete as there are many vehicle tasks not covered. This annex elaborates on some of these tasks.
One alternative approach to regulating tractor trailer fuel consumption would be to simply regulate the tractor based on standard loads tied to engine power rating. Tractors could be grouped into power ranges such as low-, medium-, and high-horsepower categories, and corresponding GVW values applied. Each of these power categories would have separate fuel consumption targets. See Figure 8-2-1.
Consider the single vehicle units shown in Figure 8-2-2 with the same GVW rating and the identical power train and chassis. For the purpose of this discussion it is assumed that the flat bed unit is used for heavy loads such as steel or lumber and the box truck is used for lighter density cargo such as courier packages. If the mass metric (gal/cargo ton-mile) were used then there would be strong incentive to minimize vehicle tare weight so that the cargo mass term in the metric could be increased thereby improving performance. This would have a clear benefit for the flat bed truck as the cargo is of sufficient density to benefit from the lighter vehicle. However for the box truck with low density cargo, the incentive for reduced tare weight may not provide any direct benefit to the shipper. In addition, when the mass metric is applied to the box truck, it would give preference to a lighter smaller box which would undermine the volumetric value of the vehicle. A metric based on volume (gal/cargo ft3-mile) would resolve this particular application.