Colin Fiske, Coalition for Responsible Transportation Priorities Executive Director
Transportation is the movement of people (or things) from one place to another. Without delving too far into basic physics, it’s fair to say that movement on this planet – and therefore transportation – requires energy. The source of that energy, and its impacts on the world around us, can have enormous impacts. Most prominently, the practice of burning fossil fuels to generate energy for transportation is one of the leading causes of our worsening global climate crisis.
Fortunately, there are lots of other sources of energy with much lower impacts. Before we review some of those options, though, it’s important to discuss the critical role of energy efficiency in the way we design our transportation systems. Because whichever energy source is used, smaller amounts of required energy translate into smaller environmental impacts.
When Americans think of energy efficiency in transportation, they likely first think of “fuel economy,” or how far a car can go on a gallon of gas (or a kilowatt-hour of charge for an electric vehicle). Because our current transportation system is dominated by cars and trucks, this is indeed an important aspect of efficiency. A big, heavy pickup truck or SUV can use many times more energy per mile than a small sedan. And driving any vehicle at higher speeds and for longer distances almost always requires more energy. But let’s not forget that cars and trucks aren’t the only way to get around!
Among modes of transportation, the most energy efficient are generally the ones that require moving only yourself (i.e., walking) or use small and lightweight devices like bikes, scooters, wheelchairs and skateboards. In fact, the bicycle is arguably the most efficient form of transportation of all, as measured by energy expended per mile.
Generally, for passenger vehicles, a car or truck is so heavy that the energy from the motor or engine is almost entirely devoted to moving the vehicle; the weight of the vehicle’s occupants has a negligible impact on energy expenditure. Buses and trains require more energy to move than a private vehicle, but also can carry many more people, so they are much more energy efficient per passenger mile. E-bikes are even more efficient—almost as efficient as a traditional bike—because they weigh so little compared to a car, truck or bus.
As we move on to a review of some of the common energy sources in transportation, then, it’s important to remember that modes of transportation like walking, biking and taking the bus are almost always going to be more efficient—and environmentally friendly—than driving by yourself in a private vehicle, no matter what energy source moves you along.
Food is the oldest transportation fuel, and still one of the most important. Food is what powers us when we walk, bike and roll. The environmental impacts of food depend a lot on the diet of the person involved, and a full examination of these issues is beyond the scope of this article. But if walking or biking causes you to eat more than you otherwise would (which it may or may not), you can generally decrease the environmental impact of your transportation with practices like eating lower on the food chain, eating more local food, and eating food produced using sustainable practices.
Fossil fuels – mostly gasoline, but also diesel, natural gas, jet fuel and propane – still provide the vast majority of energy for transportation in the United States. Fossil-powered transportation is extremely inefficient, with only about a quarter of the energy released by combustion actually used to move the vehicle (the rest is mostly lost as heat). The combustion of fossil fuels for transportation is the country’s biggest source of climate pollution. The extraction, processing and combustion of fossil fuels are also leading sources of many other toxic and health-harming air and water pollutants, causing a wide array of cancers, cardiovascular and lung diseases in humans, as well as damaging or destroying many terrestrial and aquatic ecosystems.
Electric vehicles comprise a small but growing share of the United States vehicle fleet. Currently less than 10 percent of vehicles sold in the US are electric, but their numbers are rising fast. Electric vehicles are much more efficient than their fossil-powered counterparts, with more than three quarters of energy from the battery used to actually move the vehicle. This means that even in areas with dirty electric grids (think coal), EVs almost always have lower emissions than fossil-powered vehicles. In California, with a relatively cleaner grid, EV-associated emissions are even lower. However, electric cars are heavier than fossil-powered cars of the same size, so the type of vehicle matters a lot when assessing energy efficiency. Just like gas guzzlers, big electric trucks and SUVs are an extremely inefficient way to move people around, requiring more energy to operate than a smaller vehicle and generating more impacts in their manufacture.
Some of the biggest environmental impacts of electric vehicles are associated with the minerals used in their batteries, where the energy is stored. Mining for these minerals has major impacts on ecosystems and front-line communities. Moreover, it is likely that some of the crucial “rare earth” minerals are actually rare enough that there just won’t be enough on the planet to convert all vehicles to electric—at least as long as we continue to make ever-larger cars and trucks with even more massive batteries.
Hydrogen fuel cells combine hydrogen with oxygen from the air to produce energy for moving a vehicle, and water vapor as a byproduct. All hydrogen fuel is chemically identical by the time it’s pumped into a vehicle, but to trace its lifecycle impacts it is color-coded according to how it was originally produced. The two most commonly discussed categories are gray and green, with “gray” hydrogen made from fossil fuels, while “green” hydrogen is made from water using renewable electricity.
Thus, although hydrogen vehicles are called “zero-emission,” only green hydrogen is really a zero-emission fuel. Unfortunately, almost all hydrogen fuel on the market today is gray, meaning it comes from natural gas or coal. Recent research also emphasizes the need for careful monitoring of supply lines, because hydrogen is prone to leaking and acts as a potent climate pollutant when it escapes into the atmosphere.
Hydrogen’s use as a transportation energy source is of particular interest in situations where large vehicles need to travel longer distances than current battery-electric vehicles can manage. Locally, the Humboldt Transit Authority has committed to hydrogen buses for their future zero-emission fleet because currently available battery-electric buses don’t have the range needed for many of our long rural routes.
A wide variety of fuels derived from biological sources are also used to power vehicles, and their environmental impacts vary as widely as the feed stocks and processes used to make them. By far the most commonly used biofuel today is ethanol derived from corn, which is blended into most gasoline in the US. Unfortunately, corn ethanol and many other biofuels are at least as bad for the climate as the fossil fuels they are meant to replace. They also come with other impacts, related to – in the case of corn ethanol – the massive amounts of pesticides and fertilizers used to grow the crop and the diversion of crops and cropland that could be used to grow food instead.
To avert the worst climate chaos and reduce other environmental impacts from transportation, our top priority should be to travel more efficiently. That means to walk, bike or roll for our trips whenever possible; to take public transit when we can’t walk, bike or roll; and only when none of these options are available, to drive a personal vehicle. It also means that we need to reduce the size of our personal vehicles and avoid driving at high speeds and for long distances whenever we can. Finally, it means switching the vehicles we’re still using from fossil fuels to more efficient, less damaging sources of energy. Mostly, this will mean electricity. Where we need to use other energy sources like hydrogen, we also need to do a lot of work to minimize the environmental impacts of those fuels throughout their life cycles.
Most of these measures can’t be meaningfully achieved through individual action alone. They require systematically redesigning our communities, investing in public transportation, and cracking down on car manufacturers. These are just a few of the urgent collective challenges we face in the effort to redesign today’s environmentally damaging and energy-wasting transportation systems.