Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
• Enhanced Cab Improvements – Gap reduction between tractor and trailer, improved
bumper, underside air baffles, fuel tank fairings, and wheel well covers. These
technologies currently are available for retrofit. Per unit mpg improvements are
estimated at approximately 2.4 percent (Vyas et al., 2002).
• Basic Trailer Improvements – Rounding of front and back edge curvatures. These
options currently are available for purchase with new trailers, with a per unit mpg
improvement estimated at about 1.3 percent (Vyas et al., 2002).
• Additional Trailer Improvements – Front fairings and side skirts may be retrofitted
onto existing van trailers, and currently are available. Per unit mpg benefits are
estimated between 1.0 and 2.0 percent for front fairings, and between 4.2 and
7.8 percent for side skirts (CARB, 2008a).
• Planar Boattail Plates – Devices to reduce aft-end trailer drag, currently under
development and demonstration. Potentially available for retrofit, but most suitable to
conventional van trailers due to configuration constraints. Per unit mpg
improvements are estimated between 2.8 and 4.0 percent (TIAX, 2008; Frey and Kuo,
2007).
• Vehicle Load Profile Improvements – This option involves covering flatbed freight
with tarpaulins and keeping load profiles low in order to smooth airflow.
Improvements can be made immediately at very low costs, resulting in per unit mpg
improvements of about 2.5 percent (Frey and Kuo, 2007). This strategy is limited by
the relatively small fraction of fleet using flatbeds. In addition, implementation of this
strategy relies upon the cooperation of the vehicle operator, who may have no
incentive to expend the required time and effort.
Technologies that reduce energy consumed to overcome rolling resistance generally offer
smaller improvements compared to aerodynamic technologies. Low-rolling resistance
tires can result in between 2.7 and 4.8 percent reduction in mpg for each truck (Vyas et al.,
2002; Frey and Kuo, 2007). Single wide tires are estimated to provide a full 6 percent fuel
consumption improvement, with an additional 4.0 percent estimated with future
technology improvements (NESCCAF/ICCT, 2009).
For weight reduction strategies, EPA estimates that a 3,000-pound reduction in truck
weight increases its fuel efficiency by 1.8 percent (U.S. EPA, 2004c). This estimate is
consistent with the 0.6 percent improvement per thousand pounds of weight reduction
noted above (NESCCAF/ICCT, 2009). It is estimated that pursuing weight reduction for
heavy-duty trucks could improve mpg between 5 and 10 percent (Vyas et al., 2002). A
related strategy involves replacing conventional wheels with aluminum wheels, estimated
to improve fuel efficiency by 2.0 percent as a result of the associated weight reduction
(TIAX, 2008). Reduction strategies will reduce both mechanical friction and the energy
required to accelerate the truck from a stop. In fact, weight reduction strategies should be
even more effective for urban operations due to the increased number of starts and stops,
relative to highway driving. As such, weight reduction can reduce GHG emissions from
all trucks in the fleet, from short-distance delivery trucks to long-haul trucks that travel
primarily over the highway.
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