5.1 National Benefits
By using an idling fuel-consumption rate of 1 gal/h, the estimated annual overnight idling
fuel use (in gallons) is equal to the number of truck idling hours, as shown in the last column in
Table 1. Long-haul trucks idling overnight consume more than 838 million gallons of fuel
(20 million barrels) annually (base-case estimate). Using alternatives to overnight idling could
save much of this fuel and reduce emissions and operation costs. Short-distance trucks and other
heavy-duty vehicles (such as transit buses, intercity buses, school buses, and railroad
locomotives) also idle for various reasons. If these vehicles are included, the estimated fuel
consumption due to idling climbs to 3.2 billion gallons (76 million barrels) annually.
most of this usage could not be avoided by using the technologies discussed in this report.
Table 6 summarizes the energy use and CO
emissions impact for each option over the
entire year (heating and cooling). This baseline estimate assumes that the direct-fired heaters are
operated 10 h/d in the winter and that idling is used to provide cab/sleeper cooling for 4.5 h/d in
the summer, with 100% market penetration in the eligible class 7 and class 8 trucks, for each
technology. It represents the upper bound on energy savings benefits for the assumed number of
actual benefits of each alternative to idling would be lower for lower rates of
market penetration. In particular, note that electrification impacts are estimated by assuming that
all trucks could use electrified stops, and so all trucks and parking spaces would have to be
electrified and the spaces would have to be used by an average of 1.5 trucks per day (because
there are more trucks than parking spaces). Both scenarios are unlikely. Actual impacts would, of
course, depend on the actual number of idling hours. A survey should be undertaken to estimate
actual current idling patterns in the United States.
Several conclusions can be drawn on the basis of the information in this table. First, any of
the listed alternatives has significant potential to reduce all impacts compared to idling overnight.
Even the direct-fired heater, which is only assumed to be used 85 days per year, reduces total
energy use, petroleum use, and CO
emissions by about 40% over the whole year and by about
85% for the period when it is used. Auxiliary power units reduce energy and petroleum use and
emissions by more than 80% for the entire year. Electrification could achieve almost 70%
energy savings, reduce CO
emissions by 74%, and reduce CO emissions and petroleum use by
more than 99%. Energy storage options are also expected to significantly reduce idling impacts.
Data are considered too preliminary to make conclusions about the relative potential to reduce
the emissions. Most pollutants are reduced by using energy-saving alternatives to idling.
Data are not available on fuel consumed by off-highway vehicles during idling.