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

8. SUMMARY OF RESULTS AND CONCLUSIONS
During this year-long project, the six instrumented Class-8 trucks logged almost 700,000 miles and
consumed over 100,000 gallons of fuel while undertaking 1,100 trips and visiting 37 states in the US
and one Canadian province. The vehicles were equipped with a suite of sensors and a DAS that
allowed the researchers to collect 60 channels of data at a rate of 5 Hz resulting in a very extensive
(290+ GB), and information-rich database. The channels included information such as instantaneous
fuel rate, engine speed, gear ratio, vehicle speed, and other information read from the vehicle’s
databus; spatial information gathered from a GPS device; instantaneous tractor and trailer weight
obtained from devices mounted on the six participating tractors and ten trailers; and weather
information acquired from an on-board weather station. Three of the six instrumented tractors and
five of the ten instrumented trailers were mounted with NGSWBTs and the others with regular dual
tires.
8.1 SUMMARY OF COLLECTED DATA
The information that was collected was divided into short- (less than 100 miles) and long- (over 100
miles) haul trips; and the total, moving, stopped, and idling time and fuel consumed were calculated
for all of the participating truck combinations. While short-haul trips presented proportionally larger
idling times than that experienced in long-haul trips (i.e., 69% of the total time spent of the trip vs.
49.5% of the total time, respectively, or close to a 3-to-2 ratio), the former consumed a significantly
larger proportion of the total fuel while idling than the latter (i.e., a ratio of 3-to-1, or 21.21% vs.
6.7%, respectively). It is worth noticing that short-haul trips were a very small portion of total trips
(2%).
As expected, the largest proportion of idling time, and in consequence, fuel consumed while idling,
corresponded to overnight parking (idling intervals of more than four hours). In the case of long-haul
and total (short- and long-haul) trips, about 50% of the total idling time was spent in idling intervals
that last more than four hours with about 45% of the total idling fuel consumed in these idling
intervals.
8.2 TIRE COMPARISON
The information gathered in the study also permitted the computation of fuel efficiencies for Class-8
trucks as a function of the type of tires mounted on the tractor and trailer. These calculations, which
were made using fuel consumption information obtained from the vehicles’ databus, showed an
overall fuel efficiency above 6.0 mpg. This level of fuel efficiency is on the upper limits of today’s
large-truck fleets and is mostly a result of Schrader Trucking being a very technologically minded
company and its excellent programs in driver training and the extensive vehicle maintenance
(including, for example, maintaining a constant tire pressure).
The nearly 700,000 miles logged during the data gathering phase of this study were divided into the
four tractor-trailer tire combinations (i.e., Duals-Duals, Duals-NGSWBTs, NGSWBTs-Duals, and
NGSWBTs-NGSWBTs) and fuel efficiencies were computed for 100-mile segments for any given
category. The results showed that there is always an improvement in fuel efficiency with respect to
the base case (Duals-Duals) when NGSWBTs are involved. Moreover, the fuel efficiency
improvement increases as the number of NGSWBTs on the truck increases, with observed
improvements of around 6% when either the tractor or the trailer was equipped with NGSWBTs, and
more than 9% when both were mounted with these type of tires. Due to various circumstances, the
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