Transportation

Transportation currently accounts for the largest proportion of U.S. greenhouse gas emissions of any sector (27%) and approximately 70% of U.S. oil use. Corporate Average Fuel Economy (CAFE) standards (and since 2012, the accompanying greenhouse gas emissions standards), have had the largest impact of any U.S. energy efficiency policy. Average fuel economy for light-duty vehicles has improved from approximately 13.5 miles per gallon (mpg) in 1975 to 24.9 mpg in 2017. During this period, passenger cars experienced impressive growth in horsepower and moderately larger vehicle weights (first chart).1 The second chart shows the improvement in real-world miles per gallon of several different light duty vehicle types. However, the immediate future of fuel economy standards is unclear, as the Trump administration has proposed to weaken future standards while barring state emissions standards. 2

As the U.S. reconsiders the fuel economy standards it established in 2012 (shown in chart above), other countries are strengthening fuel economy targets for their own fleets. China, South Korea, Japan, and the European Union are considering stronger fuel economy standards than the U.S., and their regulations will likely have important impacts for U.S. competitiveness in the auto market, as well as for U.S. greenhouse gas emissions and energy use overall.

Medium- and heavy-duty vehicles often have higher energy impacts relative to other highway transportation modes, due to their cargo requirements and lower fuel economy. In particular, the heavy truck segment was responsible for approximately one-quarter of total energy consumption, total gasoline and diesel consumption, and the carbon dioxide emissions for all highway transportation in 2017, in spite of the fact that it was only responsible for 9% of the vehicle miles traveled. Additionally, the vehicle miles traveled by this segment are projected to increase by more than 30% by 2050.3 Advances in fuel economy, utilizing alternative freight modes like rail and waterways, alternative fuels in highly efficient engines (such as compressed natural gas and especially renewable natural gas – a prime example of redirecting energy waste to productive energy use with a wide variety of applications),4 and streamlining logistics will likely be important to keep this segment energy-productive, and reduce local particulate, NOx, and carbon emissions.

Electric vehicles (EVs) in the light duty segment (which include battery electric, plug-in hybrid, and fuel cell electric vehicles) present significant efficiency gains over conventional vehicles, with battery electric cars estimated to be twice as efficient as a conventional car on a well-to-wheel basis.5 The U.S. market for these vehicles has grown quickly in the last decade, driven in part by Zero-Emission Vehicle mandates in select states, and federal and state tax credits. From 2015 to 2018, the annual U.S. sales of EVs increased by more than a factor of three, to 361,000, primarily due to battery electric vehicle growth. The U.S. currently has an estimated 1.3 million electric vehicles, and there are 44 different makes and models of plug-in hybrid and battery electric vehicles on the U.S. market as of March 2019. Additionally, as of 2019, eight EV models can travel over 200 miles on a single charge.6

EVs require wide availability of EV charging infrastructure, to mitigate the market barrier caused by range anxiety.7 The number of charging stations available in the U.S. has grown dramatically in the last 10 years, expanding in number and geographical coverage. As of August 2019, there were 25,533 charging stations, including a total of 74,529 charging outlets, that were Level-2 or Direct Current Fast Charge (DCFC) stations that are capable of charging most vehicles in 20-30 minutes.8 This is a 5,600% increase in chargers relative to 2009, when it was estimated that less than 500 charging stations were installed nationwide.9

Since 1970, Americans have nearly tripled the number of vehicle miles traveled by cars and trucks. This has led to a sustained rise in traffic congestion, resulting in increased energy waste, air pollution, and costly infrastructure degradation. One 2018 study estimated that traffic congestion costs the average American 97 hours, or $1,348 a year, and quantified the top 10 most congested urban areas in the United States, including the hours lost and costs per driver.10

Efficiency in the transportation sector is related to the efficiency of the vehicles, but also to the load factor, which reflects vehicle occupancy. These factors can be combined to consider the passenger miles per gallon of gasoline equivalent (pmpGGE), which quantifies the efficiency of moving one person one mile at a given vehicle fuel economy and vehicle occupancy.11 On a pmpGGE basis, rail options tend to be the most efficient travel modes (57 pmpGGE), but domestic flights, which exhibit the lowest fuel economy (0.46 mpgGGE), are surprisingly efficient per passenger due to a high load factor (averaging 113 passengers per flight) — a reflection of airlines’ efforts to ensure planes fly full. In contrast, transit buses currently exhibit lower pmpGGE (30) than cars (39) due to lower average levels of national bus ridership. However, during high ridership periods, transit bus pmpGGE is estimated to be over four times higher (132), surpassing all other national average pmpGGEs.12 This illustrates the value of increasing not only fuel economy, but the utilization of such modes.13