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

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
containers) to long-haul intermodal rail, with reductions decreasing with shorter
distances. An international study estimated the efficiency of rail freight to be 14 grams per
ton-kilometer (g/ton-km) for the entire U.S. railroad system; however, this includes the
more efficient bulk cargo transport trains. The efficiency for intermodal (container) trains,
which would carry most of the freight shifted from truck to rail, is in the range of 35 to
50 g/ton-km. These figures compare with an average truck efficiency in the United States
of about 150 g/ton-km (Buhaug et al., 2008).
Significant caveats must be considered when comparing nominal GHG reductions per
ton-mile, however. One factor that must be considered is the distance of the movement.
The greatest reductions per ton-mile occur for the longest-distance moves. For a given
door-to-door movement, the truck haul is much more likely to use one vehicle in a direct
route. For rail, the cargo must be moved by a drayage truck from the shipper to the
railhead. Terminal equipment, including yard trucks, straddle carriers and other lifting
devices, then transfer the container or truck trailer to flat cars. Smaller locomotives, know
as switching engines, move the cars to configure the train. The very efficient rail line haul
(the long-distance portion) must then be followed by the terminal and drayage activity on
the destination end. Because the rail network is less dense than the highway network, the
rail route may be less direct than the highway route. Because of the drayage moves in
particular, which may range from 50 to over 200 miles, most of the GHG emissions
advantage of rail disappears at distances less than 400-500 miles, and the maximum
benefits are only gained at over 1,000 miles.
A second factor to be considered is the potential for shifting particular commodities. Only
a limited number of commodities are amenable to shipment by both truck and rail.
Heavy, lower-value commodities such as coal, grain, and iron ore will travel by truck only
for short distances because of the higher labor and fuel cost of trucks and restrictions on
weight-carrying capacity of bridges and highway pavements. Most heavy commodities
move by rail, which is engineered to carry larger, heavier loads and realize economies of
scale. The costs savings of moving by rail generally offset the slower and sometimes less
reliable transit times of rail. Lighter, higher-value commodities are generally dependent
upon trucks’ generally higher speed and reliability (except perhaps for transcontinental
movements). Thus, only commodities with more moderate weights and values may be
considered for shipment by both modes.
In addition to the type of commodity, the volume of the commodity being moved must be
considered. An individual rail car carries the equivalent of many truck loads. If the total
volume of a commodity moving between a pair of cities is low, or the shipments are
infrequent, it may not be economical for the shipper or the railroad to switch from truck to
rail. The final factor is the network. The U.S. rail network has about half the mileage
today that it had in early 1900s. Many rail lines have been abandoned as uneconomical
because population and industry have shifted location, and trucking’s more direct and
timely service has become increasingly important with the rise of “just in time” supply
chains to avoid warehousing. Reinvestment in abandoned lines would be needed to once
again expand the reach of the rail system.
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