Rolling Smokestacks (2000)

Cleaning up America's trucks and buses
March 2003

If you have ever stood on a street corner as a large truck or bus accelerates from a stop, you are acutely aware of diesel pollution. Like passenger cars, trucks have become cleaner since pollution controls were first required in the 1970s. But the degree of cleanup has been a fraction of what regulators have asked of cars. As a result, trucks are now a substantial source of air pollution and other environmental problems. Although trucks account for under 6 percent of the miles driven by highway vehicles in the United States, they are responsible for --

  • one-quarter of smog-causing pollution from highway vehicles
  • over half the soot from highway vehicles
  • the majority of the cancer threat posed by air pollution in some urban areas
  • 6 percent of the nation's global warming pollution
  • over one-tenth of America's oil consumption

Improvements to conventional diesel trucks are an absolute priority, but cleaner alternative fuels and advanced technologies are the ultimate solution.

Cleaner Diesel: Improvements to Today's Trucks 

Advances in pollution-control technologies will make it possible to slash truck pollution almost as quickly as oil refiners can—or are required to—supply cleaner diesel fuel.

This figure indicates some of the technologies that could be applied to clean up big diesels. With strong regulatory guarantees that ensure these cleaner trucks stay clean over their million-mile lives, truck pollution can be reduced by over 90 percent. Advances in engines and truck designs can also increase truck fuel efficiency, which will save truckers money and reduce global warming emissions as trucks travel farther on each gallon of diesel fuel.

Green Technologies: Alternative Fuels and Advanced Technologies 

Cleaner diesel engines can go a long way toward reducing air pollution and global warming emissions from trucks. But moving beyond diesel to cleaner alternative fuels (such as natural gas) is essential for polluted urban areas where health protection is a priority today. And advanced technologies, such as fuel cells, are a vital part of the long-term solution. Transit buses, school buses, and urban delivery vehicles are particularly well suited to these green technologies and are the logical launch point for broader introduction.

Vehicles powered by alternative fuels and advanced technologies have inherently low emissions, both of smog-forming pollutants and of soot. In addition, they emit fewer of the heat-trapping gases that cause global warming. The figures below illustrate just how much difference these technologies can make. They show how many cars-worth of emissions a model year 2000 transit or school bus would produce, if powered by various technologies.

Although diesel engines will become cleaner, these alternatives will retain their advantage in curbing pollution because the cleanup technologies developed for diesel engines can also be used with natural gas or hybrid engines. But the ultimate solution to combustion is fuel cells: high-efficiency engines that emit no pollution.

Policies for Progress: Regulations, Incentives, and Research
Realizing the potential of cleaner diesel and green technologies requires strong policies to move trucking onto a greener path. The Environmental Protection Agency's recently proposed diesel engine regulations are an excellent first step, requiring that emissions from new trucks show a 95 percent reduction of smog-causing nitrogen oxides over current levels and a 90 percent reduction of soot. The same regulations would also require oil companies to remove 97 percent of the sulfur currently present in diesel fuel, an essential step for enabling exhaust-control equipment to achieve and retain high levels of pollution reduction. But tighter tailpipe standards alone are not enough. Regulators must ensure that vehicles are as clean on the highway as they are during certification testing—and that they stay clean over their million-mile lifetimes. And they should require cleanup of existing fleets of dirty trucks and buses.

Cleaning up diesel is an absolute necessity. But policymakers also need to recognize the special benefits of intrinsically clean vehicles: those powered by alternative fuels or advanced technologies. These green trucks and buses offer an extra measure of public health protection in urban areas, and many can also help reduce global warming pollutants. Regulations, incentives, and research are all needed to push these technologies onto the road as soon as possible. The place to start is high-priority markets like transit buses, school buses, and urban trucks.

Although not a replacement for strong regulations and incentives, public research is the foundation for environmental gains in trucks and buses. Reducing emissions of the heat-trapping gases responsible for global warming is a particularly challenging task that should be addressed through research to boost truck efficiency and to find suitable fuels that contain less carbon, the primary global-warming pollutant.

Green Truck Path: National Benefits 

The benefits of cleaner and more efficient diesel, alternative fuel, and advanced technology trucks could be substantial, allowing trucks to remain at the heart of America's commerce while curbing their impact on public health and the environment. We constructed a detailed model of the US truck sector to evaluate the potential energy and environmental benefits of a national green truck strategy. By the time cleaner trucks permeate the truck population in 2030, we estimate that the gains over a "business-as-usual" base case could include

  • Preventing emission of one-quarter of a million tons of toxic soot
  • Keeping over 60 million cars-worth of smog-forming exhaust out of the air *
  • Doubling truck travel without increasing oil use
  • Reducing global warming pollutants by 26 percent

Today's diesel trucks emit more soot and smog-forming pollution than even a coal-fired power plant, for every unit of energy they burn. But new technologies and fuels can clean up America's rolling smokestacks, allowing trucks and buses to finally pull their weight in protecting the planet. 

* Based on the pollutants emitted by the average passenger vehicle on the road today.

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