Cleaner Transit -- New Buses
Transportation in the United States is a major contributor to global warming: our vehicles alone put out more carbon dioxide than most other countries emit from all their sources combined. Cars and small trucks make up two-thirds of the transportation emissions problem, so getting people out of their cars -- and into buses, for example -- and providing efficient vehicles powered by renewable fuels are both high priorities.This shift to mass transit not only decreases emissions of carbon dioxide, but also reduces air pollution, lowers oil imports, and curtails congestion. Simply taking transit more often lowers the impact of our travel, but improving the technology of bus service can greatly enhance the benefits of transit.
Although taking transit is environmentally preferable to driving, today's diesel buses are by no means "green" machines. The black puffs of smoke from bus tailpipes inject urban air with harmful pollutants that have been linked to a host of health problems, including lung and heart disease, breathing problems, and perhaps cancer. Now, however, despite a history of slow technological change, new buses running on alternative fuels are entering the market. By reducing dirty, smelly diesel smoke, these clean buses are improving transit's environmental appeal, thereby boosting public support and increasing ridership.
The first stop in the evolution of cleaner buses has been to use cleaner-burning fuels. The new combustion buses use the same engine technology as diesel buses, modified to burn ethanol, methanol, propane, biodiesel, or natural gas. The cleanest versions, which burn natural gas, are gaining interest among transit agencies nationwide because they are substantially cleaner than diesel buses and are often less expensive to run. Their emissions of soot and the pollutants that cause smog are 40 percent below those of the diesel buses they replace. However, they offer less impressive gains in alleviating global warming, since they reduce emissions of heat-trapping gases by only 5 to 10 percent.
The next stop is hybrid and electric buses. Hybrid buses combine a combustion engine with electric motors and batteries. These are still in the demonstration stage, but they promise lower emissions and higher fuel economy than traditional combustion buses. Electric buses, powered by batteries, are also in the early market stage and produce zero emissions.
The most promising stop in the evolution of bus technology is fuel cell buses powered by hydrogen. Using electric engines that combine hydrogen and air to produce electricity, fuel cell buses release no pollution -- the only by-product is water. However, heat-trapping gases may be emitted indirectly as a result of the process that produces hydrogen for the fuel cells. When the hydrogen is harvested from natural gas, the indirect emissions associated with fuel cell buses are roughly half those of diesel buses. When the hydrogen is harvested from water, using energy from renewable sources like solar power, the indirect emissions are eliminated completely. Commercial application of fuel-cell technology in buses will pave the way for a technology that holds tremendous promise for the automotive and even electric power markets.
Reducing air pollution from buses offers real economic benefits to urban areas struggling to address air-quality problems. UCS estimates that in Los Angeles, for example, the emissions saved over the life of a natural gas bus are worth $56,000 in avoided costs for controlling industrial air pollution -- costs that businesses and consumers would otherwise pay to meet clean-air requirements. A hydrogen fuel cell bus could save $151,000 in these costs over its lifetime.
So far, clean air requirements have been a driving force behind the move to alternative-fuel buses. As global warming becomes a high international priority, however, technologies like fuel cell buses that do double duty -- both zeroing out air pollution and slashing heat-trapping-gas emissions -- will become even more important. But putting such buses on the road requires government leadership. Federal research programs to continue developing these technologies, as well as transit funding programs that help purchase advanced buses, are critical.
Some local transit authorities have already made a commitment to purchase the cleanest buses available. These forward-thinking agencies offer an excellent model for transit authorities nationwide. In addition to using federal incentives, transit agencies in some regions can access state and local funds collected from automobile users (such as registration fees or fuel taxes) to fund cleaner transit options.
Clean buses are a reality today. Nearly 1 bus in 20 is now powered by alternative fuels. Combustion buses using natural gas are transporting people in Houston, Los Angeles, Miami, and Portland. Fuel cell buses will be cleaning the air in Chicago this summer and in Vancouver, British Columbia, within the year. As more cities join the caravan, advances in bus technology will draw all our vehicles toward a cleaner future.
