|Fig. 1: Freight train transhipment. (Source: Wikimedia Commons)|
The transportation sector plays a significant role in our daily lives, enabling us to move people and goods from one place to another. However, the emissions generated by transportation are also a major contributor to climate change, responsible for 26% of all global greenhouse gas (GHG) emissions.  In this paper, we will analyze rail and trucking energy consumption in the context of freight transportation.
We will begin by identifying the contributions to emissions of the two modes of transportation, and then examine their fuel efficiency. Well then discuss the economics of freight rail and trucking to discern the degree to which fuel efficiency influences overall cost structure. Finally, well discuss what the implications are on reducing emissions.
Overall, reducing emissions from the transportation sector is crucial for mitigating the impacts of climate change and creating a sustainable future. This paper aims to provide an overview of transportation emissions from freight rail and trucking, as well as the extent to which the difference in emissions plays a role in mode choice.
As of 2014, freight rail resulted in 21.2 metric tons of GHG emissions per million ton-miles while trucks emitted 154.1 metric tons of GHG per million ton-miles.  This makes rail over seven times more energy efficient than trucking in terms of GHG emissions. This discrepancy carries into fuel efficiency as well. Trains measure in at 477 ton-miles per gallon of fuel, while for trucks it's only 145 ton-miles per gallon. [2,3] This is primarily because the rolling resistance of steel wheels on rails is less than that of rubber tires on the road.
Despite being far less fuel-efficient, trucks are still the most common mode of freight transportation globally. For example, trucking composes 77% of all freight transportation in Europe while rail only accounts for 8%.  One reason why the difference in energy efficiency doesn't have a large impact on choice of mode is that fuel makes up a relatively small portion of costs, representing 21% of trucking costs and an even smaller portion for rail.  The process of transhipment (for example unloading containers from rail cars, loading them onto trucks, and then delivering goods to their final destination, as pictured in Fig. 1) represents 62% of cost for an average freight rail shipment. 
As a result, rail tends to be poorly suited for short trips. Additionally, rail tends to be less reliable, making trucks more popular for high-value and time-sensitive goods. Therefore, shifting freight from truck to rail has little to do with improving fuel efficiency.
It is clear that reducing emissions from transportation is crucial for mitigating the impacts of climate change. Given that rail emits one-seventh of the greenhouse gasses as trucking per ton-mile, it's tempting to say that it should be the mode of transportation of choice for shippers. But the respective cost structures and reliability of each mode make the difference in fuel efficiency almost immaterial to cost and give trucking the upper hand.
© Sam Forman. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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