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Class-8 Heavy Truck Duty Cycle Project Final Report - Center for ...

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vehicle is hauling light or heavy loads since most of the <strong>Class</strong>-8 truck trips fall into the second weight<br />

category.<br />

To do this, the search engine of the DCGenT Prototype was used to parse the data by truck-tire<br />

combination and vehicle load level. The vehicle weight was divided into four categories: 1) Tractor<br />

Only (trips made without any trailer), 2) Light Load (total vehicle weight between 24,000lbs and<br />

44,000lbs); 3) Medium Load (total vehicle weight between 44,000lbs and 62,000lbs); and 4) <strong>Heavy</strong><br />

Load (total vehicle weight between 62,000lbs and 80,000lbs). As in the previous sub-section, 100mile<br />

segments were considered <strong>for</strong> which the fuel efficiency was computed and counted as one<br />

observation. Table 22 presents the results of this analysis. Under each load level category, the<br />

column labeled “Avg. FE” contains the average of the fuel efficiencies across all the 100-mile<br />

segments in which each particular truck-tire combination was divided, with the column immediately<br />

to the right presenting the percent difference in fuel efficiencies when comparing against the base<br />

case (i.e., the case in which the tractor and trailer are equipped with dual tires). For all load levels<br />

considered, there is always an improvement in fuel efficiency with respect to the base case (i.e.,<br />

Duals-Duals). Notice also that fuel efficiency improvement increases as the number of NGSWBTs<br />

increases. Moreover, <strong>for</strong> the particular case in which all tires are NGSWBTs, there are considerable<br />

improvements in fuel efficiency with respect to the base case (10+%), and those improvements are<br />

more significant as the load level increases.<br />

Table 22. Fuel Efficiency as a Function of Load Level and <strong>Truck</strong>-Tire Configuration<br />

Load Level<br />

<strong>Truck</strong>-Tire Tractor Only<br />

Configuration<br />

1<br />

Avg. FE % Diff with<br />

Light Load<br />

Avg. FE<br />

Medium Load <strong>Heavy</strong> Load<br />

(mpg) Duals-Duals<br />

1<br />

% Diff with Avg. FE<br />

(mpg) Duals-Duals<br />

1<br />

% Diff with Avg. FE<br />

(mpg) Duals-Duals<br />

1<br />

% Diff with<br />

(mpg) Duals-Duals<br />

Duals-<br />

Duals<br />

9.01 0.00% 8.06 0.00% 7.17 0.00% 6.24 0.00%<br />

Duals-<br />

NGSWBTs<br />

NA NA 8.61 6.75% 7.48 4.34% 6.50 4.22%<br />

NGSWBTs-<br />

Duals<br />

NA NA 8.63 7.06% 7.51 4.76% 6.56 5.16%<br />

NGSWBTs-<br />

10.52 16.77%<br />

NGSWBTs<br />

1<br />

Fuel efficiencies computed using collected databus in<strong>for</strong>mation.<br />

8.79 8.94% 7.93 10.60% 6.88 10.20%<br />

As in the previous subsection, a series of tests of hypothesis were per<strong>for</strong>med to statistically<br />

corroborate these results. The null hypothesis (i.e., there is no difference between the distribution of<br />

fuel efficiencies <strong>for</strong> any tire combination that has NGSWBTs and that of the base case; see Eq. 11)<br />

was tested against an alternative hypothesis stating that the average of the distributions of the fuel<br />

efficiencies of any tire combination that has NGSWBTs are larger than that of the base case (see Eq.<br />

12). Fig. 78 to Fig. 81 show the distribution of fuel efficiencies computed <strong>for</strong> 100-mile segments <strong>for</strong><br />

trucks with Duals-Duals, Duals-NGSWBTs, NGSWBTs-Duals, and NGSWBTs-NGSWBTs tire<br />

combinations, respectively, <strong>for</strong> vehicles carrying heavy loads (i.e., total vehicle weight above 62,000<br />

lbs). As the figures show, the distributions of fuel efficiencies are very close to normal distributions;<br />

moreover, since the sample size in any case is large, the Central Limit Theorem applies as in the<br />

previous case. That is, it is possible to assume that the average of any one of the fuel efficiency<br />

distributions under consideration is normally distributed and it is an unbiased estimator of the true<br />

distribution mean.<br />

92

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