NTRD-02 Final Project Report The Effects of Low Rolling Resistance ...

4.3 Evaluation of the Candidate Cycle
After synthesizing the composite cycle, several evaluations were made, including comparisons of
the cycle to the target dataset. Analysis of speed v. acceleration distributions for the composite
cycle and the raw data showed a good match; a few outlying points in the raw data were not
included in the micro-trips used in the cycle, and thus the representation is good from that
standpoint. The speed histogram of the composite cycle matches the speed histogram from the
raw data, showing that the time-at-speed for the cycle is representative of the raw data. Full
details can be seen in the detailed report on the cycle development (Palacios and DeFries, 2007).
A number of statistics were calculated so that the characteristics of the cycle could be compared
to the characteristics of the target dataset (see Table 1). Because the micro-trips in the cycle
were selected for their non-idle speed and acceleration characteristics, other statistics that are
calculated and compared do not necessarily reflect as close a match between the test cycle and
the raw data.
Table 1 shows that the average second-by-second speeds of the selected cycle and target
database are similar, although the cycle speeds are slightly lower than those in the target dataset.
The difference results from high-speed trips in the target dataset, which were few in number but
very long. Also, the micro-trips selected for the cycle have a longer average length (duration in
seconds and distance traveled) compared to the average for the target vector. This is due to the
exclusion of all-idle micro-trips and micro-trips of less than 20 seconds for cycle building.
Finally, Table 1 shows that the square of the length of T-C was very low, both for the two subcycles
separately and for the two when combined. This indicates a good fit of the driving
conditions (speed and acceleration) in the selected cycle, compared to the target database.
Table 1. Comparison of Data Set and Test Cycle Characteristics.
Total Time
(s)
Average sxs
Speed
(mph)
Total
Distance
(miles)
13
Average
Micro-Trip
Time
(s)
Average
Micro-Trip
Distance
(miles)
Micro-
Trips
(count)
Target 242,724 26.2 1767.2 139.2 1.0 1744 -
Final
Square
of L.
of T-C
Sub-Cycle 1 2,594 24.5 13.6 259.4 1.4 10 0.21
Sub-Cycle 2 3,186 24.8 18.0 289.6 1.6 11 0.20
Sub-Cycles
1&2 5,780 24.7 31.6 275.2 1.5 21 0.19
The final version of the Texas Drayage Truck Test Cycle is illustrated in Figure 8.