When Susan Banks was 8 years old and growing up in a small Pennsylvania town, she and her mother would take the Number Nine bus downtown to shop. They had a car, but Susan's mom, always thinking green, knew that mass transit was better for the environment: the fewer cars on the road, the better. However, when it was time to go back home, they'd wait for the bus not at the terminal, but in the window of Main Street's Woolworth's. The reason - the fumes.

Back then, standing behind a bus was perhaps more dangerous than standing in front of one. Buses, and more specifically, the diesel engines that propelled them, were a major source of particulate matter, nitrogen oxides and air toxics. All of these pollutants can cause serious health problems, but things have changed.

Now, the bus that takes Susan to her ad exec job in Manhattan is nothing like the ones outside the old five and dime. Thanks to the work of the U.S. Environmental Protection Agency (EPA) and the mass transit community, today's buses are cleaner, quieter and more efficient. Because of a number of cost-effective solutions from exhaust filters to idle-reduction strategies, we are working together to make the black puff of smoke, once so characteristic of buses and diesel engines, a thing of the past.

BACKGROUND

For the past century, diesel engines have been America's economic workhorse - reliable, fuel-efficient and long-lasting. These were qualities that made diesel engines very attractive for a variety of uses, including fleet vehicles. However, because diesel engines operate at high temperatures using low viscosity fuel, they can emit a lot of pollution - large amounts of nitrogen oxides and particulate matter, both of which contribute to serious public health problems.

These problems are manifested by thousands of premature deaths, hundreds of thousands of asthma attacks, millions of lost work days and numerous other health impacts. Because these engines are so widely used, reducing their emissions to protect public health has been one of the EPA's most important air quality challenges.

Both Presidents Clinton and Bush knew the rewards of committing to a new national investment in energy innovation in order to create cleaner diesel engines. The 2007 Heavy Duty Highway Rule (HDHR), adopted by President Clinton's administration and implemented by President Bush, has helped make America's air cleaner than it was 30 years ago, and will help it continue to get cleaner.

In fact, diesel engines and the vehicles they power have become dramatically cleaner. Today's buses emit only oneeighth the pollution of a bus built in 1980, and when the buses featuring the engines compliant with the HDHR hit the road, it will take 60 of them to emit the same amount of soot given off by the tailpipe of one 1980 model year bus. In terms of public health, this means long-term annual benefits of more than $70 billion - 17 times the cost of compliance.